Antioxidant

Antioxidant Defence for Abiotic Stress Tolerance

The harmful effects of ROS are prevented by the presence of lipid soluble antioxidants (a-tocopherol and carotenoids), water-soluble reductants (glutathione and ascorbate) and antioxi-dant enzymes such as catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and superoxide dismutase (SOD, EC 1.15.1.1) present in plant cells (Desikan et al. 2004). In response to stress, some of the osmolytes accumulate in plant cells, besides a role in scavenging of free radicals and protecting enzymes (Krishnan et al. 2008). The ability to activate protective mechanisms, such as an increase in the activity of scavenging enzymes, is vital for oxidative stress tolerance. Transgenic improvements for abiotic stress tolerances have been achieved through detoxification strategies by overexpressing the enzymes involved in oxidative protection. For example, salt or thermal stress treatment inhibited the growth of wild tobacco and caused increased lipid peroxidation, while overexpression of...

Nonenzymatic Antioxidants 331 Ascorbic Acid

Among the small molecular antioxidants in plants, ascorbate is most abundant and is most concentrated in leaves and meristems (reviewed by Ahmad et al. 2010b) . It is about five to ten times more concentrated than GSH in leaves (Ishikawa et al. 2006) . AsA is present in high concentration in fruits, especially citrus fruits, but the concentration in fruits is not always higher than in leaves (Davey et al. 2000). Some fruits such as blackcurrants and rose hips are famous for their exceptionally high ascorbate content (Ishikawa et al. 2006). AsA occurs in all subcellular compartments, and the concentration varies from 20 mM in the cytosol to 300 mM in chloroplasts (Noctor and Foyer 1998). The synthesis of AsA takes place in mitochondria and is transported to other cell compartments through a proton electrochemical gradient or through facilitated diffusion (Horemans et al. 2000). Franceschi and Tarlyn (2002) reported the presence of ascorbate in the phloem sap of A. thaliana. Other...

Antioxidants as a Protective Means

Radiation and oxidative damage have always been common on Earth (Rothschild and Mancinelli 2001). When cells are desiccated in the light, chlorophyll molecules continue to be excited, but the energy not used in carbon fixation will cause formation of singlet oxygen (Kranner et al. 2005). Photoprotective mechanisms can dissipate much of it. These mechanisms include dissipation as heat via carote-noids, photorespiration, and morphological features that minimize light absorption. ROS such as superoxide and singlet oxygen are produced in chloroplasts by photo-reduction of oxygen and energy transfer from triplet excited chlorophyll to oxygen, respectively. In addition, hydrogen peroxide and hydroxyl radicals can form as a result of the reactions of superoxide. All these ROS are reactive and potentially damaging, causing lipid peroxidation and inactivation of enzymes (Smirnoff 1993). Free radical scavengers are the two water-soluble antioxidants reduced glutathione (GSH) and ascorbate...

ROS Signaling and Antioxidant Responses

Fig. 3 Major physiological changes described in plants treated with heavy metals (HM2+). In excluder plants metals accumulate in the root, where most of the alterations occur. The cell wall can act as a sink, but when this barrier is overridden, metals enter the protoplast probably through ion channels (for example Ca2+-channel). Part of the uptaken metal can be expelled by transporters of the HMA, possibly loading them in the xylem. Plasma membrane NADPH-oxidases are activated to generate O2 , which is converted to H2O2 in the apoplast to serve as substrate of cell wall peroxidises to stiffen cell wall polymers. H2O2 can also oxidize membrane lipids, generating peroxide lipid radicals (FA-OO ), or permeate to the cytoplasm where antioxidant enzymes must control cellular levels of ROS (SOD, CAT and APX). On the other hand, metals would activate phytochelatin synthase (PCS) triggering the synthesis of phytochelatins (PC). These biothiols would form complexes that are thought to be...

Nutritional Antioxidants And Polyphenolic Flavonoids

The beneficial health effects attributed to the consumption of fruits and vegetables are related, at least in part, to their antioxidant activity.12 Edible plants contain several hundred different antioxidants.3 Natural antioxidants include vitamins C and E, carotenoids (such as P-carotene and tomato's lycopene), and polyphenolic fla-vonoids (such as those present in grapes, berries, licorice, ginger, nuts, and olive oil). For a compound to be defined as an antioxidant it must satisfy two basic conditions Low-density lipoprotein (LDL) oxidation is considered to be a hallmark of early atherogenesis. Nutritional antioxidants can affect LDL oxidation directly or indirectly, via modulations of arterial wall cell oxidative state and its subsequent capacity to oxidize LDL. Dietary antioxidants can inhibit LDL oxidation by several means 1. Scavenging of free radicals, chelation of transition metal ions, or protection of the intrinsic antioxidants in the LDL particle (vitamin E and...

Antioxidant Metabolites

Next to GSH, several other metabolites participate in the cellular antioxidant network to combat an increased ROS accumulation during metal stress. In the following paragraphs, these metabolites and their potential involvement in the oxidative challenge mediated by Cd and Cu are discussed. In plants, AsA has a regulatory role during cell growth, cell wall biosynthesis, photosynthesis and cell differentiation. This metabolite is present in all subcellular compartments including the apoplast, chloroplast, cytosol, vacuoles, mitochondria and peroxisomes. In chloroplasts and mitochondria, AsA plays a key protective role by decreasing the damage caused by ROS formed during photosynthetic and respiratory processes (Potters et al. 2002). Ascorbic acid directly reacts with all different ROS (1O2, O2- , H2O2, -OH) in which AsA is being oxidised (Fig. 2). As mentioned above, the oxidation reduction ratio of AsA reflects the cellular toxicity level in Cd- and Cu-exposed plants. Besides its role...

Antioxidant Systems Under Cd Stress

5.2.1 Enzymatic Antioxidants Systems A variety of proteins function as scavengers of ROS such as superoxide dismutase (SOD), catalase (CAT), enzymes of the ascorbate-glutathione cycle, peroxiredoxin and thioredoxin families. The main response for the removal of ROS appears to be via the induction of SOD and CAT activities, and by the induction of GR to ensure the availability of reduced glutathione for the synthesis of Cd-binding peptides. This fact could be related to the inhibition of APX activity probably due to glutathione and ascorbate depletion (Gomes-Junior et al. 2006). Different effects were observed in antioxidant enzymes depending on Cd concentration, period of treatment, the plant tissue studied and the plant itself. SOD plays an important role as a defence mechanism carrying out the catalytic dismutation or disproportionation of O2 - with production of water and hydrogen peroxide. While Cd-dependent reduction of SOD activity has been reported in wheat (Milone et al. 2003)...

The Level of Free Radicals Defines the Type of Plant Reaction

Low levels of free radicals are apparently able to stimulate animal macrophages and neutrophils (Finkel 1998). Such role of radicals is not established for plants however, ROS also play a critical role in the initiation and maintenance of a hypersensitive response upon an encounter with a pathogen. Thus, we hypothesized that pretreatment of plants with oxidative stress-generating compounds would prime them to tolerate a higher level of stress. Since it was not clear what level of oxidative stress is required to generate such response, we first attempted to identify the optimal external concentration of RB that would be used for pretreatment. Seedlings at 2 weeks post-germination were incubated for 2 hours in medium containing 0.02 iM, 0.1 iM or 0.5 iM RB and then were transferred to liquid medium containing 20 M or 50 M of MMS. These concentrations of MMS were previously shown to induce HRF (Puchta et al. 1995). Interestingly, it was observed that pretreatment with 0.5 M RB...

Plant Antioxidant Systems

Oxygen reactivity strongly influenced the evolution of aerobic organisms making necessary efficient strategies allowing cells to cope with the inevitable ROS production in their metabolism. This led to the development of a complex and redundant antioxidant network in all aerobic cells. The term antioxidant is referred to metabolites, such as ascorbate, glutathione, pyridine nucleotides, which are present in concentrations lower than oxidizable substrates but which can prevent or and revert their oxidation. These metabolites are involved in network of reactions in which several enzymes control their biosynthesis and redox state or utilize them as reducing substrates for ROS detoxification. These networks define the capability of a specific antioxidant metabolite to counteract ROS production and to control their levels. They act in synergy with enzymes, such as superoxide dismutase (SOD) and catalases (CAT) that dismutate specific ROS to less reactive or harmless chemical species. Due...

Effect of Ethylene on the Antioxidant System during Leaf Senescence

The oxidative metabolism has an important role at cellular level when senescence takes place. During leaf senescence there is an overproduction of reactive oxygen species (ROS) such as superoxide anion (O2-), hydroxyl radicals (OH'), hydrogen peroxide (H2O2) and singlet oxygen (1O2) that may cause damage and cell death. However, they are also products of the normal enzymatic reactions in peroxisomes, glyoxysomes, and chloroplasts. The harmful ROS are controlled and balanced by the antioxidant systems present in leaves. The leaf cells act as a defense response against the accumulation of ROS by increasing catalase (CAT) and superoxide dismutases (SOD) activity. But other enzymatic and non-enzymatic antioxidants are also involved, such as ascorbate, reduced gluthatione (GSH), a-tocopherol and carotenoids (Foyer et al. 1994 Bartoli et al. 1996 Hodges et al. 1996, 1997a, 1997b). The ascorbate-glutathione cycle, also known as the Asada-Halliwell cycle, is the most important antioxidant...

Coordinated UpRegulation of the Antioxidant Network

Much of the earlier literature focused on the response of multiple components of antioxidant defenses in plants suffering traumatic oxidative stress and bear out this notion of coordinated regulation of an antioxidant network (Foyer and Mullineaux, 1994 Noctor and Foyer, 1998 Asada, 1999). The activities of enzymes, levels of various antioxidants, and control at the levels of translation, RNA turnover, and de novo transcription have been described for the regulation of antiox-idant defenses under these severe stresses. The above reviews provide many individual examples of the types of control on the expression of genes of the antioxidant network. Fig. 2. An example of an antioxidant network spanning subcellular compartments. The regeneration of ascorbate (Asc) at the plasma membrane (PM after Horemans et al., 2000). Asc is either directly re-reduced by a -type cytochrome-mediated electron transfer (cyt b) or by the action of a cytoplasmic NADH-MDHA oxidoreductase (R). Alternatively,...

Effects of Pomegranates on Antioxidant Status

Pomegranate anthocyanins have been shown to scavenge superoxide (O -) and hydroxyl (Off ) radicals to prevent lipid peroxidation in rat brain homogenates.16 An extract from pomegranate peel fed to rats for 14 days reduced lipid peroxidation in the liver as well.41 The plasma antioxidant status of humans fed pomegranate juice is elevated over control subjects,42-44 suggesting that pomegranate polyphenols are bioavailable and are able to elevate the antioxidant capacity of the body. Pomegranate polyphenols have been shown to increase the concentrations of the endogenous antioxidant glutathione (GSH) in mouse peritoneal macrophages,42 while pomegranate peel extract, fed to rats for 14 days, prevented the carbon tetrachloride-induced loss of peroxidase, catalase, and superoxide dismutase in the liver.41 GSH is the major antioxidant system in cells, donating electrons to H2O2 and becoming oxidized to GSSG in a reaction catalyzed by glutathione peroxidase. Intracellular antioxidant content,...

Reconfiguration of the Antioxidant Network and the Regulatory Role of Glutathione

There are numerous studies on a wide range of plant species, both in the natural environment and under laboratory conditions, showing that successful acclimation is associated with changes in antioxidant defenses (Rauser et al., 1991 De Vos et al., 1992 Walker and McKersie, 1993 Chaumont et al., 1995 Kampfenkel etal., 1995 Iturbe-Ormaetxe etal., 1998 Bruggemann et al., 1999 Hernandez et al., 2000). During the life of a plant, one may expect that antioxidant defenses will undergo subtle adjustments, with some components increasing their levels or activity, while others are decreasing. Recent evidence for this comes from the study ofan Arabidopsis APX1 null mutant, in which only a mild growth diminution was apparent that was accompanied by alterations in the expression of an-tioxidant defense genes as well as a range of genes involved in many other cellular functions (Pnueli et al., 2003). Similar observations have been made in transgenic tobacco with suppressed cytosolic APX...

C ROS Antioxidants Jasmonic Acid and Ethylene

JA signaling for response to wounding of plants has been suggested to be mediated by H2O2 which, in turn, stimulates gene expression in the vicinity of the wound site that could help prevent opportunistic infections, deter herbivores, and repair wounds (Orozco-Cardenas et al., 2001). JA pre-treatment of plants can also protect tobacco and Arabidopsis against ozone damage, an effect that may, in part, be due to changes in expression of antioxidant defense genes such as APX (Orvar et al., 1997 Rao et al., 2000). Similarly, a coordinated regulation of the expression of genes of glutathione metabolism such as glutathione reductase (GR) and the enzymes of glutathione synthesis occurs upon treatment of Arabidopsis plants with JA (Xiang and Oliver, 1998). It is not clear that all these effects of JA on ROS antioxidant metabolism are linked, but if they are, then those of the whole plant response to environmental challenges that are influenced by JA must involve a coordinated regulation of...

Growth ROS Antioxidants and Auxins

The induction of defense responses can also lead to a down-regulation of genes associated with the vegetative growth of the plant. For example, in the vtcl mutant, a slow growth rate has been attributed to elevated levels of ABA rather than partial depletion of its ascorbate content (Pastori et al., 2003). Furthermore, H2O2 treatment of Arabidopsis protoplasts led not only to MAPK-mediated up-regulation of antioxidant defense gene expression, but also to a down-regulation of auxin-regulated genes that might be implicated in meristem growth (Kovtun et al., 2000). This may reflect a recently described convergence of kinase-mediated signaling that would coordinate both defense and growth responses to H2O2 (Moon et al., 2003). Conversely, auxin treatment of plant tissues may induce ROS production and also induce expression of antioxidant defense genes such as GSTs (Chen and Singh, 1999 Joo et al., 2001 Pfeiffer and Hoftberger, 2001). Again, these data indicate that there is a two-way...

Conclusions on Hormone Signaling and ROSAntioxidant Metabolism

It is clear from the above considerations that antioxidant metabolism can be profoundly influenced by, and in turn influence, signaling pathways nominally directed by one or more hormones. It has been suggested by many authors that the overlap in the type of genes induced by chemically diverse molecules may be reconciled by invoking a common effect on ROS at the cellular level (reviewed in Garreton et al., 2002). However, it is also clear that, in all cases, complex feedback regulation occurs by which ROS and antioxidants can influence the potency of hormones, especially those associated with stress. Thus, circular pathways of regulation have to be invoked to link up these diverse observations (e.g. Overmyer et al., 2000). Perhaps the most compelling part of the relationship between cellular redox state (influencedby antioxidants such as glutathione) and signaling pathways is that key players in the pathways studied to date have either been shown to be or may be redox regulated. These...

Glutathione and Antioxidant Defense

Even in the absence of an enzyme, glutathione is able to interact rapidly with free radicals such as superoxide and the hydroxyl radical (Polle, 2001). In addition, glutathione plays an important role in peroxide detoxification through several possible enzyme systems. First, GSH can regenerate ascorbate (Fig. 1), either directly or through the action of various enzymes able to catalyze DHA reduction, including glutaredoxins (GRX) and GSTs (Wells et al., 1990 Trumper et al., 1994 Shimaoka et al., 2000 Urano et al., 2000 Dixon et al., 2002). Secondly, both GRX and GSTs can also reduce hydroperoxides to the corresponding alcohol or H2O (Bartling et al., 1993 Collinson et al., 2002). Third, certain PRXs are regenerated by a GR GRX system (Rouhier et al., 2002). Fourth, specific glu-tathione peroxidases (GPXs) exist in plants (Eshdat et al., 1997). Genes encoding plant GPXs have been

Flavonoids as Antioxidants in Plants Under Abiotic Stresses

Flavonoids make a relevant contribution to the response mechanisms of higher plants to a plethora of abiotic stresses. In addition to the long-reported functions as screeners of damaging short-wave solar radiation, flavonoids have been suggested as playing key functions as antioxidants in stressed plants, by inhibiting the generation and reducing reactive oxygen species (ROS) once formed. The ROS-scavenging properties of flavonoids are restricted to few structures, namely, the dihydroxy B-ring-substituted fla-vonoid glycosides. This structure-activity relationship conforms to the well-known stress-inducedpreferentialbiosynthesis ofdihydroxy B-ring-substituted both flavones and flavonols. These flavonoids, especially the derivatives of quercetin, have been shown to greatly affect the movement of auxin at intra-and intercellular levels, and hence to tightly regulate the development of individual organs and the whole plant. The effectiveness of flavonoids to inhibit the activity of the...

Down Regulation of the Antioxidant Network Evidence from Lesion Mimic Mutants

In addition to ROS production, and of more relevance to this chapter, there could arguably be a down-regulation of expression of key enzymes of the antioxidant network which would point to coordinated control and therefore cross-talk between pathways. A good example of this concept may be the mode of action of LSD1. The prefix LSD means lesion simulating disease and refers to the way in which the gene was first identified in Arabidopsis. The mutant lsd1 is one of a number of so-called lesion mimic mutants identified in several plant species that either show spontaneous but discrete HR-like lesions when not exposed to a pathogen, or lethal, spreading, uncontrolled lesion formation under non-permissive conditions. Such environmental conditions include a change in the light environment, exposure to an avirulent pathogen, or to ozone (Dietrich et al., 1994 Bowling et al., 1997 Gray et al., 1997 Takahashi et al., 1999 Overmyer et al., 2000 Devadas et al., 2002). LSD1 is a regulatory...

Free Radicals Active Oxygen Species and Antioxidants

The highly reactive free radicals, along with hydrogen peroxide (H2O2), are collectively termed active reactive oxygen species (AOS ROS). While the intracellular glassy state must curtail molecular and AOS mobility, and thus interaction, during the process of desiccation, intracellular structures are highly vulnerable as conditions for radical generation are enhanced (Vertucci and Farrant, 1995 Pammenter and Berjak, 1999 Walters et al., 2005a). Possession and effective operation of a suite of antioxidants is of prime importance during dehydration of orthodox seeds, and again as soon as water uptake commences by the desiccated cells (Pammenter and Berjak, 1999). Additionally, non-enzymic antioxidants are likely to confer protection during the desiccated state in seeds (Bailly, 2004) and in the cells of any organism or structure capable of surviving extreme desiccation. Most studies on AOS and antioxidants have been focused on the final stages of seed desiccation, but in his review...

Drought Stress Induced Reactive Oxygen Species and Antioxidants in Plants

Aerobic metabolism in plants results in the generation of reactive oxygen species (ROS). ROS are produced constantly in plants under physiological steady state condition, and plants have evolved to efficiently scavenge and maintain the levels of ROS at non-damaging levels. However, plants when exposed to either abiotic or biotic stress conditions, the production of ROS exceeds their scavenging capacity, leading to an outburst of highly reactive oxidative species capable of inflicting significant damage to the membranes, DNA, and proteins. On the other hand, these reactive molecules when maintained under non-damaging levels are useful signalling molecules involved in relaying stress signal to activate acclimation and defence mechanism. Drought or water deficit stress is one of the major abiotic stresses which induces the production of different kinds of ROS including both free radicals such as superoxide (O2-), hydroxyl radicals (OH), per-hydroxy radical (HO2) and alkoxy radicals (RO)...

Ginger as an Antioxidant

Ginger has a high content of antioxidants and has been grouped as one of the spices with good antioxidant activity, with 1.8 index rating (Chipault et al., 1952). This makes it a free radical scavenger (Lee and Ahn, 1985). Sethi and Aggarwal (1957) reported that dried ginger has weak antioxidant properties. The antioxidant property of ginger in comparison with other common spices is given in Table 15.8. Fugio et al. (1969) studied the antioxidant properties of the chemical components of many spices and found that the shogaol and zingiberene found in ginger exhibited strong antioxidant activities. The antioxidant activity of ginger is dependent on the side-chain structures and substitution patterns on the benzene ring. Twelve compounds showed higher activity than a-tocopherol. Mainly, the antioxidant activity is exerted by gingerol

Antioxidant Flavonoids and the Antioxidant Machinery of Plants

3.1 Stress-Induced Alterations in the Antioxidant Enzymes System There is a large consensus that a well-coordinated system of constitutive antioxidant defenses is activated in plants upon a plethora of abiotic stresses (for a recent review, see Gill and Tuteja 2010). Superoxide dismutase (SOD), the well-known first-line of defense against ROS generation (aimed at removing the highly reactive superoxide anion) (O2-), and both ascorbate peroxidase (APX) and catalase (CAT), the enzymes that are devoted at detoxifying the relatively stable H.O2, have long been reported to play a key role in protecting plants from stress-induced oxidative injuries (Schwanz and Polle 2001a, b Polle 2001). The extent to which the activity of antioxidant enzymes increases upon stress imposition has been widely reported to correlate positively with tolerance to various abiotic stresses (Hern ndez et al. 1999, 2000, 2003 Tattini et al. 2005 Sekmen et al. 2007), although it has been also reported that the...

Antioxidant Systems

The halophytic plants display a cascade of events upon exposure to environmental stresses leading to metabolic disturbance. The cascade of events include physiological water-deficit abscisic acid-regulated stomatal closure in leaves, limited CO2 availability, over-reduction of electron transport chain in the chloroplast and mitochondria and finally generation of reactive oxygen species (ROS). These ROS are highly toxic and in the absence of protective mechanism in the plant can cause oxidative damage to proteins, DNA, and lipids (Mittler 2002 Miller et al. 2010). Additionally, this may also lead to alteration in the redox state resulting in further damage to the cell (Mittler et al. 2004). To regulate the ROS levels, plant cells are evolved with complex enzymatic and nonenzymatic antioxidant defense mechanisms, which together help to control the cellular redox state under changing environmental conditions. A correlation between enzymatic and nonenzymatic antioxidant capacitance and...

Antioxidant Defense

Plants possess several antioxidative defense systems to scavenge ROS in order to protect themselves from oxidant stress, including that caused by heavy metals (Benavides et al. 2005). These include both non-enzymatic antioxidants such as GSH and ascorbate (ASA), and enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (POD). The unique structural properties in GSH such as broader redox potential, abundance, and wide distribution render it as a good non-enzymatic scavenger of ROS in plants. Treatment of the hyperaccu-mulating ecotype of S. alfredii with the GSH synthesis inhibitor L-buthionine-sulfoximine (BSO) resulted in a significant damage in leaves with a concomitant Polyamines such as putrescine (Put), spermidine (Spd), and spermine (Spm) are polybasic aliphatic amines that play a major role in various physiological and developmental processes in plants. Polyamines also have an...

Antioxidants

The role of reactive oxygen species (ROS) in male fertility has come under increasing speculation with regard to their physiologic and pathologic effects. Elevated levels of ROS are known to compromise sperm function and viability (damage of spermatic nuclear DNA). This oxidative stress is derived from excessive production of ROS and or impaired antioxidant defense mechanisms in the semen.21 The use of antioxidant nutrients, such as selenium, glutathione, vitamin E, and vitamin C, has produced benefits in relation to sperm health. Glutathione is an important part of sperm antioxidant defense and has been repeatedly shown to have a positive effect on sperm motility when subjects took supplements with this antioxidant.24-26 In one interesting study, 600 mg of glutathione was administered intramuscularly to subjects, every other day for two months. Compared to subjects in a placebo group, men in the treatment group experienced a statistically significant effect on sperm motility,...

Free Radicals

Free radicals are believed to play a role in the pathogenesis of MS. Persons with MS have elevated concentrations of markers of nitric oxide (NO) production, including nitrate and nitrite, in their cerebrospinal fluid (CSF), blood, and urine. Research suggests that NO has a role in the axonal degeneration and impairment of axonal conduction, disruption of the blood-brain

Generation of O Ho Oh and other ROS in Plant Cells

Most ROS in plant cells are formed via dismutation of superoxide, which arises as a result of single electron transfer to molecular oxygen in electron transfer chains principally during the Mehler reactions in chloroplast (Asada 1999, Asada 2006). In case of photosynthetic electron transport O2 uptake associated with photo-reduction of O2 to superoxide (Fig. 2) is called Mehler reaction, in honor of the discoverer (Mehler 1951). Although photo-reduction of oxygen is an important alternative sink for the consumption of excess energy, but it is always associated with the generation of toxic ROS (Varnova et al. 2002). If the accumulation of ROS exceeds the capacity of enzymic and non-enzymic antioxidant systems to remove them, photodynamic damage to photosynthetic apparatus ensues, which leads to cell destruction. The dearth of NADP+ in PS I due to redox imbalance causes spilling of electron on to molecular oxygen triggering the generation of O2- The regulated activation of Calvin cycle...

Environmental Stress and Production of ROS

Although it is clear that ABA can impose an oxidative stress, an enhancement capacity of oxidative stress tolerance may imply that the plant need to mobilize the whole antioxidative defense systems to resist oxidative damage in stressed plant tissues. Sgherri et al. (1994) found that during drought stress of Boea hygroscopica, antioxidants such as glutathione and ascorbate accumulated. In sunflower seedlings there is an induction of antioxidant enzyme activities and increase in GSH contents when plant reached a moderate level of water deficit stress (Bruke et al. 1985). Lipid soluble antioxidants such as a-tocopherol, p-carotene, total thiol content along with a coordinated response of glutathione reductase and ascorbate to limit the free radical depending effects of water stressed wheat leaves. But their finding clearly suggests the view that ROS formed at membrane level after exposure to moderate water stress. Bartoli et al. (1999) showed that ascorbate peroxidase, glutathione...

ROS Production during Senescence

The following hypothesis of sequences of events during senescence involving ROS has been put forward. Initially membrane lipid got degraded by lipid degrading enzymes like phospholipase D, phosphatidic acid, phosphatase etc., inducing release of free fatty acids. Peroxidation of free fatty acids (containing cis, cis 1,4 pentadiene moiety) by lipoxygenase, and nonenzymatically catalyzed by free radicals, leads to the production of ROS, promotion of burst of ethylene and acceleration of senescence .

Possible Roles of Radicals in Plants

Infection caused by pathogens that is recognized by a gene-for-gene interaction (Keen 1990) as incompatible results in the activation of the salicylic acid-dependent pathway, initiation of the nitric oxide (NO) signaling cascade and SA-induced massive production of free radicals (Vlot et al. 2008). The roles that these radicals play in the limitation of pathogen spread include, direct killing of pathogens, killing infected cells or and cell wall strengthening in cells surrounding infected cells (Chamnongpol et al. 1998). It is a curious fact that apparently the first wave of radicals produced occurs regardless of whether a pathogen is recognized (an incompatible interaction) or not (a compatible interaction) (Grant et al. 2000). It can be suggested that the initial boost of free radicals is involved in a certain type of systemic signaling, perhaps a warning which plants produce to prepare non-treated tissue for incoming pathogens. The second larger burst of...

The Role of Radicals in DNA Damage and Signaling in Plants

Plants have certain spontaneous levels of radicals in cells and certain spontaneous levels of HRF. It can be suggested that to increase the recombination rate, an extra level of radicals is required. It seems that inhibition of catalases was not sufficient to raise the concentration of free radicals to damaging levels. As to the mode of action of catalase, it has a low affinity for H2O2 and removes only excess levels of hydrogen peroxide (Willekens et al. 1997). For a cell, the function of catalase is 'duplicated' by enzymes of the ascorbate-glutathione cycle with high affinity for H2O2 (Willekens et al. 1997). It has been hypothesized that when plants are exposed to AT, catalases are inhibited, and H2O2 endogenously produced is scavenged by ascorbate peroxidase (APX). This idea was indeed supported in the experiment in which RB and AT were applied simultaneously. Plants that were treated with both agents had significantly higher recombination frequencies than those that were treated...

Cellular Localization of Ascgsh Cycle

The sub-cellular localization of the components of ASC-GSH cycle in plant cells has been widely discussed. The presence of ASC and GSH pools has been demonstrated in almost all cellular compartments (Fig. 2) (Noctor and Foyer 1998). Moreover, the ASC pool in each compartment seems to be specifically regulated. In cytosol and chloroplasts, ASC concentration is in millimolar range and the reduced form is predominant, at least in physiological conditions. In the apoplast and within the vacuole, ASC content is in micromolar range and its redox state, expressed as ratio between ASC and ASC+DHA, is shifted towards DHA (Foyer and Lelandais 1996, de Pinto et al. 1999, De Gara and Tommasi 1999, Hernandez et al. 2001). ASC seems to be the only antioxidant which has buffering capability in the apoplast, where it is involved in growth and defense processes (de Pinto and De Gara 2004).

Heat Shock and the Defense Responses Activated in the Redox Sensitive Pathways

These last results underline that the route for understanding redox signaling still requires a deeper study in order to better understand the role played by each cellular compartment in the interplay between ROS and antioxidant networks. Asada, K. The role of ascorbate peroxidase and monodehydroascorbate reductase in H2O2 scavenging in plants. pp. 715-735. In J.G. Scandalios ed. 1987. Oxidative Stress and the Molecular Biology of Antioxidant Defences. Cold Spring Harbor, Cold Spring Harbor Laboratory Press, USA. Asada, K. and M. Takahashi. Production and scavenging of active oxygen in photosynthesis. pp. 227-287. In D.J. Kyle, C.B. Osmond and C.J. Arntzen eds. 1987. Photoinhibition. Elsevier, Amsterdam. Chew, O. and J. Whelan, and A.H. Millar. 2003. Molecular definition of the ascorbate-glutathione cycle in Arabidopsis mitochondria reveals dual targeting of antioxidant defences in plants. J. Biol. Chem. 278 46869-46877. Del Rio, L.A. and F.J. Corpas, L.M. Sandalio, J.M. Palma, M....

ROSinduced Cell Death Network

Many of the genes recruited in the first steps of the signaling are involved in the generation of ROS necessary for triggering PCD (NADPH oxidases, extracellular peroxidases), whereas others are responsible for the modulation of ROS levels (catalases, APXs, and other antioxidant enzymes) (Gadjev et al. 2008). Alterations in sodium, potassium, and calcium ion fluxes are among the earliest events that follow elevation in ROS levels. The transient Ca2+ oscillations are stress-specific and can lead to various downstream effects, including PCD, through the numerous Ca2+-interacting proteins, like calmodulins and calcium-dependent protein kinases (Harper et al. 2004, Yang and Poovaiah 2003). Ca2+ influx from intra- and extracellular sources is regulated by various ion channels and antiporters. Recently, the cyclic nucleotide-gated channel 2 (CNGC2 DND1) has been identified as an essential component in nitric oxide

ROS Signaling Pathways Regulating Potato Tuberization

An oxidative burst results in the generation of ROS, which are known to induce an intracellular signaling pathway (Grant et al. 2000). Despite a possible role of an oxidative burst in the signaling network of the tuberization process, a direct evidence for the involvement of ROS molecules in a developmental process like tuberization is rather recent. Till date, research in this field is, however, limited to the characterization and transgenic expression of the antioxidant enzyme superoxide dismutase (SOD EC 1.15.1.1) that converts two O2' radicals into H2O2 and O2. In plant systems, there are three types of SODs-MnSOD, FeSOD and Cu ZnSOD, and they are regarded as the base components in an antioxidant protective system against ROS-induced oxidative damages (Zelko et al. 2002). Of the three different SOD isoforms, Cu ZnSOD is localized in both cytoplasm and chloroplasts. A chloroplast-localized SOD (chCu ZnSOD) associated with bulb formation in lily has been isolated and characterized,...

Conclusion and Future Prospects

The present research on the role of ROS, as signal molecules, in tuber morphogenesis is too elementary to render us unable to develop an integrated view of ROS signaling pathways regulating in planta tuberization in potato. Current data show that the post-harvest development (ageing) of potato tubers is associated with an increased ROS production, however, an efficient antioxidant machinery involving the major enzymatic antioxidants, such as SOD, ascorbate peroxidase (APX) and catalase (CAT) avoids an effective build-up of oxidative damage (Delaplace et al. 2009). The production of ROS during tuber dormancy breaking vis- -vis tuber sprouting is the result of enhanced metabolic activity, such as respiration. Since similar mechanisms are thought to operate during tuber formation and tuber sprouting (Vreugdenhil 2004), the regulatory effects of ROS signal molecules on tuber induction and development cannot be ignored. Despite an unambiguous evidence for the involvement of O2 , as a...

Abstract

Degradation of membrane lipids, resulting in free fatty acids, initiates oxidative deterioration enzymatically (by providing substrate for enzyme lipoxygenase) or nonenzymatically, causing membrane lipid peroxidation. Since lipid peroxidation (both enzymatic and nonenzymatic) is known to produce alkoxy, peroxy radicals as well as singlet oxygen, these reactions in the membrane is a major source of ROS in plant cells. The spatial compartmentalization of ROS producing enzymes in specialized domain of plant plasma membrane (membrane rafts) is also a key element in the generation of ROS. However, the steady state level of ROS and its consequence in plant cells is largely determined by antioxidant systems, comprising a variety of antioxidant molecules, quenchers and enzymes. Although plants are equipped with those molecules (antioxidants) to combat enhanced level of ROS, in other circumstances plants appear to produce ROS purposefully and exploit these molecules as signaling molecules to...

Conclusion

The results of our work suggest the existence of a fine-tuned balance in the amount of free-radicals in plant cells. Cells are able to effectively regulate this balance. Apparently, the external application of radical-producing stress changes the redox balance, transcriptome and depending on the level of changes can trigger different responses. Certainly, more extensive analysis of this phenomenon is needed in the future. It is not clear how the external oxidant concentration correlates with the actual level of radicals inside the cell. It is not known whether the plant transcriptome changes upon exposure to the levels of oxidants described above. It is also not clear whether these changes are different depending on the concentration of oxidants applied. It would be also interesting to test whether pretreatment with different types of oxidative stress-generating compounds results in the same level of protection.

Abiotic Stress Responses in Plants An Overview

Plants are more and more affected by environmental stresses, especially by the devastating consequences of desertification and water scarcity which can be seen and felt all over the world. About 3.6 billion of the world's 5.2 billion hectares of dryland used for agriculture have already suffered erosion, soil degradation, and salinization. Desertification can hinder efforts for sustainable development and introduces new threats to human health, ecosystems, and national economies. This problem is catalyzed by global climate change which exacerbates desertification and salinization. Therefore, solutions are desperately needed, such as the improvement of drought and salinity tolerance of crops, which in turn requires a detailed knowledge about tolerance mechanisms in plants. These mechanisms comprise a wide range of responses on molecular, cellular, and whole plant levels, which include amongst others the synthesis of compatible solutes osmolytes and radical scavenging mechanisms....

Nutraceuticals For Treating Adrenocortical Dysfunction

Cofactor for the citric-acid cycle potent antioxidant partially restores the hydrocortisone suppression of T-helper cell activityd Unknown further research is needed Ascorbic acid, or vitamin C, is a water-soluble vitamin important for numerous physiological functions. In addition to antioxidant and immune-stimulating activity, it is also involved with tyrosine, tryptophan, norepinephrine, dopamine, thyroxine, and carnitine metabolism. A study was performed to evaluate the effect of ascorbic acid supplementation with psychological stress. The group given the ascorbic acid showed less increase in blood pressure, decreased subjective stress response, and a faster cortisol recovery.113 In one study, ascorbic acid supplementation was given to individuals undergoing prolonged exercise. Cortisol was significantly reduced immediately post-exercise, as well as epinephrine, interleukin-10, and interleukin-1 receptor antagonist.114 Evidence also shows that animals deficient in ascorbic acid...

Photoprotection Photoinhibition Gene Regulation and Environment

Key plant responses are photoprotection and photoinhibition. In this volume, the dual role of photoprotective responses in the preservation of leaf integrity and in redox signaling networks modulating stress acclimation, growth, and development is addressed. In addition, the still unresolved impact of photoinhibition on plant survival and productivity is discussed. Specific topics include dissipation of excess energy via thermal and other pathways, scavenging of reactive oxygen by antioxidants, proteins key to photoprotection and photoinhibition, peroxidation of lipids, as well as signaling by reactive oxygen, lipid-derived messengers, and other messengers that modulate gene expression. Approaches include biochemical, physiological, genetic, molecular, and field studies, addressing intense visible and ultraviolet light, winter conditions, nutrient deficiency, drought, and salinity. This book is directed toward advanced undergraduate students, graduate...

Amino Acids Proline and Amides

The contribution of Glu and Orn pathways to stress-induced Pro synthesis differs between species, and it has been shown that stress-tolerant plants are able to accumulate Pro in higher concentrations than stress-sensitive plants. Slama et al. (2008) showed a positive correlation between Pro accumulation and tolerance to salt, drought, and the combined effects of these stresses. Osmotic stress (particularly mannitol stress) led to a considerable increase of the Pro concentration in the obligatory halophyte Sesuvium portulacastrum, while the contents in soluble sugars and in Na+ remained unchanged. In drought-stressed plants, the concentration of K+, Na+, Cl-, and Pro, as well as ornithine-8-aminotransferase (8-OAT) activity increased significantly. Inversely, Pro dehydrogenase activity was impaired. Re-watering leads to a recovery of these parameters at values close to those of plants permanently irrigated with 100 of field capacity. The presence of NaCl and mannitol in the culture...

Is There Commonality Facilitating Desiccation Tolerance Among Organisms

Late embryogenesis abundant (LEA) proteins, sucrose and certain oligosaccha-rides accumulate coincidently with the acquisition of DT during orthodox seed development (Buitink et al., 2002), and particular antioxidant enzymes become prominent (Bailly, 2004). The expression of at least 16 different LEA genes (identified from a survey of only 425 cDNAs) (J.M. Farrant, 2005, University of Cape Town, South Africa, personal communication) has been found to occur in the leaves of the xero-tolerant resurrection plant, Xerophyta humilis (Baker) Dur. and Schinz during dehydration (Collett et al., 2004). The antioxidant 1-cys-peroxiredoxin, which had previously been considered to be seed-exclusive, was found to be abundantly expressed in tissues of the resurrection plants X. humilis and X. viscosa (Baker). Illing et al. (2005) also reported that sucrose accumulates only in the tissues of the desiccation-tolerant Eragrostis nindensis (Ficalho & Hiern), and not in related sensitive Eragrostis...

Reactive Oxygen Species

(Pasternak et al. 2002) and that oxidative stress enhances auxin-dependent cell cycle reactivation (Pasternak et al. 2005). Although ROS initially promote dedifferentiation and re-initiation of cell division, an inability to control levels of ROS may be a causal factor in recalcitrance of some species to undergo SE. Plants possess an arsenal of small-molecule antioxidants (ascorbate, glutathione and tocopherol) and antioxidant enzymes (including superoxide dismutases, peroxi-dases and catalase) and, in cultured tobacco protoplasts, up-regulation of the activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase follows the oxidative burst, causing reduced forms of glutathione and ascorbate to predominate. Significantly, this change does not occur in non-totipotent cells and appears necessary for the expression of totipotency (Papadakis et al. 2001). The nature of downstream events involved in wound-induced ROS signalling remains unclear. However, they may...

Processing and utilization

Soybean polypeptide is a hydrolyzed product of protein through special treatment. Generally, it consists of peptides of 3-6 amino acids. Soybean polypeptide has a high nutritional value, high digestibility coefficient and low antigenicity, and the results of experiments show that its digestibility coefficient is much better than that of protein or amino acids. Soybean poly-peptide can be used as a raw material for or additive to health foods. It has a therapeutic effect on high blood pressure and cardiovascular and cerebro-vascular diseases, and is safe and reliable. Soybean polypeptide also decreases the deposition of subcutaneous fat and increases fat burning and it is, therefore, a safe food for people who want to lose weight. Soybean polypeptide also has an antioxidant effect, and it has been claimed that the muscle cells of athletes recover faster when they imbibe a polypeptide-containing drink (Wang et al., 2004).

Conclusion and Future Perspective

Experience drought and 19.5 of the irrigated land are affected by salinity. These problems will be further catalyzed by global climate change. Prolonged environmental stresses are responsible for the production of ROS in different cell compartments like chloroplasts, mitochondria, per-oxisomes, etc. ROS attack biomolecules, viz., DNA, lipids, proteins, carbohydrates, and disturb the normal functioning of the cell. Under severe stress conditions, ROS ultimately lead to cell death. In order to withstand oxidative stress, plants are equipped with enzymatic and nonenzy-matic antioxidants. Many workers have reported the positive effects of SOD, CAT, APX, GR, MDHAR, AsA, glutathione, etc., in combating oxidative damage to the cell. To overcome the deleterious effects of abiotic stresses, plants also accumulate osmolytes and osmoprotectants such as proline and glycine betaine. These compounds are thought to play a role in osmotic adjustment and protect subcellular structures. Elevated...

Supporting Healthy Sexual Functioning For Both Genders

Ginkgo (Ginkgo biloba) has vasodilatory effects and has been shown to help men with erectile dysfunction. In two studies,16,17 men with impotence noted meaningful benefits when they took ginkgo. Ginkgo's vasodilatory effect can help both men and women who want to achieve optimal sexual function. Like arginine, ginkgo is a natural substance that enhances circulation yet ginkgo has potent antioxidant and vascular stabilizing effects as well. Thus, this herb not only serves as a treatment in addressing symptoms, but nourishes the body at the same time. The herb accomplishes this by facilitating microvascular circulation, vasodilation, and smooth-muscle relaxation.18 Ginkgo and ginseng have been shown to relax smooth muscle and thereby increase circulation.19

Adaptations to Abiotic Stresses

In order to achieve the tolerance status, three interconnected aspects of plant activity are significant damage must be prevented, homeostatic condition must be re-established, and growth must resume. At present, there are different mechanisms of abiotic stress tolerance in halo-phytes that have been proposed which include ion compartmentalization, osmotic adjustment through osmolytes accumulation, succulence, selective transport and uptake of ions, enzymatic and nonenzymatic antioxidant response, maintenance of redox and energetic status, salt inclusion excretion and genetic control (Flowers and Colmer 2008). Understanding the mechanism of tolerance in halophytes at morphological, anatomical, physiological, biochemical, and molecular levels is crucial to improve the tolerance of the crop plants and their adoption under abiotic stress conditions to exploit such problem soils. A generalized scheme for the plant's response to abiotic stresses and mechanism of stress tolerance is...

Alternative Treatments And Lifestyle Changes

N-acetyl-cysteine (NAC) is an acetylated ester of the amino acid L-cysteine. NAC has a significant ability to raise glutathione levels in the body, important for its potent antioxidant activity. NAC is also used to treat lung conditions as an expectorant and mucous thinner, and to produce anti-inflammatory effects.44 Studies suggest that NAC decreases production of pro-inflammatory cytokines, such as TNF-alpha, which have been shown to be elevated in individuals with OSA.45

Methylsulfonylmethane and Hyaluronic Acid

Both methylsulfonylmethane (MSM) and hyaluronic acid are essential for maintaining connective tissue integrity, and thus for ensuring the rigidity and firmness of the underlying cellular matrix of the airway walls. MSM has been shown to have anti-inflammatory and antioxidant properties. Anecdotal evidence suggests that MSM may be effective for addressing many conditions, including snoring and allergic rhinitis.61 Hyaluronic acid, a glycosaminoglycan, could be considered for treatment of snoring and augmentation of airway connective tissue integrity.62 Because of hyaluronic acid's visco-elastic quality, this substance may work to strengthen the connective tissue surrounding the airway and decrease obstructions.

Regulation of Light Energy Utilization

Understanding the consequences of excess light absorption requires consideration of the coupling between the light and dark reactions of photosynthesis. For any environmental factor (e.g. light or temperature) which results in a limitation of photosynthesis in the dark reactions, there is an inhibition of electron transport due to slower regeneration of NADP+, ADP or inorganic phosphate (Fig. 1). This leads to a reduction of electron carriers on the acceptor sides of both PS I and PS II, closing of PS II reaction centers and increased acidification of the thylakoid lumen. The decrease in PS II photochemistry due to closing of the traps results in higher yields of fluorescence and triplet formation. If the rate of triplet formation exceeds the capacity of carotenoids to quench triplets, net production of singlet results with associated oxidative damage. At the same time, limited availability ofNADP'1 allows molecular 02 to compete with ferredoxin as an acceptor from PS I, resulting in...

Oneelectron reactions

GSH reacts preferentially with free radicals, such as oxygen-, carbon- or nitrogen-centered radicals, whereas reducing (electron-donating) radicals such as pyridinyl radicals are unreactive toward thiols. In these reactions GSH donates hydrogen atoms, which is one of the most important biological function of glutathione. This hydrogen donor activity results in the production of the thiyl (GS') radical. Thiyl radicals are sufficiently stable so that they are readily formed and unreactive toward other hydrogen donors. The formation of the disulphide GSSG results from dimerisation of these radicals

Cell biology Nitric oxide early stress signals and cell death

The free radical, nitric oxide (NO) is a very early and highly transient metabolic signal in the stress response of cells. Laser confocal microscopy and detecting dyes, or laser photoacoutsic detection, have been effective for monitoring NO bursts in cells and plants respectively. NO is lipid soluble and diffuses in membranes. It leads to protective and or harmful reaction depending on the perturbing conditions. Damaging effects arise from the reaction of NO with other free radicals that may not be produced by enzymatic reactions 7 . With optical methods, the problems due to photodamage and toxicity must be evaluated and ruled out. Fluorescent sensors and combined techniques have produced consistent models to quantify stress and damage 8 .

Etiology And Pathophysiology

Oxidative stress from oxygen-bearing free radicals may have a causal role in autistic spectrum disorders. Oxidative stress from oxygen-bearing free radicals may have a causal role in ASD. Individuals with autism have shown increased nitric oxide in their red blood cells and increased activity of the antioxidant enzyme glutathione peroxidase in these individuals' plasma.23 Other studies have shown increased levels of such antioxidant enzymes as superoxide dismutase and xanthine oxidase in autism.24 Increased lipid peroxidation has also been observed in individuals with autism. Transferrin, an iron-binding protein, and ceruloplasmin, a copper-binding protein, which exhibit antioxidant activity, have been found to be significantly decreased in autistic children, a finding that has been linked to a loss of language skills.25 Some children with autism show elevated levels of total homocysteine, a finding strongly correlated with decreased erythrocyte glutathione peroxidase activity and...

Programmed Cell Death

The final phase of starchy endosperm development in cereal grains involves cell death. Indeed, cell death is an important part of the development and maintenance of many tissues and organs in plants and animals (Buckner et al. 2000 Krishnamurthy et al. 2000). PCD can be triggered in cells that have served their function, such as transmitting cells of the postpollination stigma and the antipodal and synergid cells in the postfertilization megagameto-phyte, or cells that die as part of differentiation, such as xylem tracheary elements and cells that recognize pathogens (Krishnamurthy et al. 2000). The regulation of PCD has been well studied in animal cells, but the process is not equally well understood in plants. The trigger for PCD can be from signals generated outside or inside the cell, and they lead to signaling events that result in a cascade of hydrolytic activity (Krishnamurthy et al. 2000). Some of the signals generated in animal cells include calcium fluxes, production of free...

Conclusions and Future Perspectives

Variety of tolerance mechanisms such as halosuc-culence, ion compartmentation (exclusion inclusion), osmoregulation, enzymaticandnonenzymatic antioxidants and maintenance of redox and energy status. Research on understanding the abiotic stress tolerance mechanism of halophytes has been on the upfront using wide array of physiological, biochemical, and molecular tools. Some of the halo-phytes (e.g., Thellungiella halophila) that tolerate adverse conditions have become the choice model systems for unraveling the different pathways associated with halophytic behavior. However, research in the context of progress in metabolom-ics, genomics, and proteomics has to be initiated in diverse halophytic species with the use of advanced techniques to gain detailed knowledge of abiotic stress tolerance.

The Functions Of Glutathione Molecular And Biochemical Aspects

In addition to the storage and transport of reduced sulphur, glutathione and or its homologues have a broad spectrum of functions in plants and animals (Figure 2). These include (A) antioxidant defence, (B) redox regulation served at the site of infection, and to a lesser extent at remote sites. H202 and SA (and perhaps also glutathione) are potential systemic messengers carrying information concerning attack to unchallenged plant tissues (Figure 1). Of the complex array of antioxidants found in plant cells, to date glutathione alone has been shown to be strongly induced and to accumulate rapidly in response to pathogen attack (Edwards et al. 1991, Vanacker et al. 2000). The effect on biosynthesis is specific to GSH and not a general effect on the synthesis of low molecular weight antioxidants. It appears to be a universal response in plants faced by pathogen attack or environmental stress, where the antioxidant defences are temporarily overwhelmed by an oxidative burst or by the...

Morphology and physiology

Desiccation tolerance is not yet fully understood in bryophytes but it does involve components present in the cells sugars, largely sucrose, and protective proteins including antioxidants and enzymes involved in protection from the generation of reactive oxygen species (ROS). A genomic approach is currently being used to catalog genes whose products play a role in responses of bryo-phytes to desiccation and rehydration, but much remains to be resolved. The sequencing of the genome of Physcomitrella patens is an important tool. Even though P. patens is not a desiccation-tolerant species, researchers now have the ability to knock out and replace its genes, which will be a powerful tool for future work.

Dietary Interventions

Dietary whole grains have also been associated with decreased cardiovascular risk. Whole-grain foods provide complex carbohydrates, dietary fiber, minerals, vitamins, and antioxidants. Research indicated that whole grain dietary intake decreases the risk of hypertension, myocardial infarction, and heart failure.87 In one study to evaluate the role of whole grains and atherosclerosis, whole-grain intake was evaluated and carotid intimal medial thickness was measured. Whole-grain intake was shown to be inversely associated with common carotid artery intimal medial thickness and intimal medial thickness progression.88 A 12-week, randomized, controlled trial compared two whole-grain oat-based cereals with two refined grain wheat-based cereals to evaluate their effects on the need for antihypertensive medications in patients with hypertension. At the end of 12 weeks, 73 of participants in the oats group versus Green tea polyphenols, particularly epigallocatechin gallate (EGCG), have been...

Artificially induced dormancy release current working hypothesis

A working hypothesis can currently be suggested (Fig. 6), in which temporary inhibition of oxidative phosphorylation may lead to respiratory and oxi-dative stress, expressed as decreased production of ATP and a temporary increase in H2O2 level. In response, the AOX pathway, glycolysis and anaerobic respiration are induced, in an as yet undefined order, to face the energy crisis, and respiration is enhanced, as reflected by CO2 evolution. Members of the antioxidant machinery and related pathways (glutathione-ascorbate cycle, GST, thioredoxin, pentose phosphate pathway) are induced in parallel to cope with the oxidative burst. Primary oxidative stress may then be amplified by inactiva-tion of CAT, extending the temporary stress situation. Inhibition of CAT activity in plant tissues in response to oxidative stress has been recorded and related

Glutathione Conjugation

This pathway assists in making fat-soluble toxins water-soluble, allowing for excretion via the kidneys. Because this pathway is glutathione-dependent, it is indirectly dependent upon the presence of sufficient cysteine and methionine in the body. Chronic alcohol intake is also strongly associated with increased oxidative stress and decreased glutathione levels.12 Vitamin C has also been shown to be effective in supporting the maintenance of glutathione levels.13 Consumption of foods that stimulate glutathione conjugation, such as orange-peel oil, turmeric, artichoke, and dill and caraway seeds, can be recommended therapeutically. If phase 1 detoxification generates excess free radicals, glutathione depletion can occur, thereby preventing or stalling the glutathione-conjugation pathway.

Supporting Detoxification Within The Body

This common herb, used frequently in the form of turmeric (Curcuma longa), has antioxidant and anti-inflammatory properties. Curcumin has been shown to help inhibit the carcinogenic effects of benzopyrene that arise from the consumption of charbroiled meat. This herb has been shown to modulate phase 1 detoxification while inducing phase 2 of the process. When 1.5 g of turmeric was given to 16 smokers and 6 nonsmokers (control subjects), it was shown that, after 30 days of consuming turmeric, urinary excretion of mutagens in smokers was nearly equivalent to that of nonsmokers. This study demonstrated that turmeric is an effective inhibitor of phase 1 detoxification, preventing the excess accumulation of toxic metabolite conversion of

DNA Damage and Repair

2000) the UV-B radiation is the most important photooxidant agent for terrestrial plants. The DNA damage can also be caused by reactive oxygen species (ROS) and free radicals produced by the UV-B radiation. This damage includes several modifications such as cross-linking, aggregation, denaturation, and degradation (Hidema et al. 2007) . The formation of 7,8-dihydro-8-oxoguanine (GO) is a common oxidative DNA lesion generated by a direct modification mediated by ROS. The GO is mutagenic and can mispair with adenine (A) during the DNA replication (Yang et al. 2001). If the resulting A GO is not repaired before the next round of the DNA replication, a C G A T transversion occurs and the opportunity for repair is lost. The A GO is repaired via the BER which is initiated by the DNA repair enzyme adenine-DNA glycosylase (Yang et al. 2001). The UV-absorbing compounds (e.g., flavonoids, anthocyanins, hydroxycinnamic acid derivatives, phenolics) accumulating in epidermal and subepidermal cell...

Small Molecules Involved In Signaling And Execution Of Hr Cell Death

Superoxide anion generation in relation to HR was first reported for potato tuber slices inoculated with an avirulent race of Phytoph-thora infestans (Doke, 1983). Subsequently, the oxidative burst has been identified in numerous plant-pathogen interactions involving different kinds of pathogens. The origin of ROI generated during the oxidative burst is not unequivocally established, but candidate reactions are the action of a plasma membrane-located NADPH-depend-ent oxidase complex and cell wall peroxidases (Wojtaszek, 1997 Grant and Loake, 2000). The cytotoxicity and reactive nature of O2-requires its cellular concentration to be carefully controlled, which can be achieved by induction of antioxidant enzymes, such as glutathione S-transferase, glutathione peroxidase, or ascorbate peroxidase (Wojtaszek, 1997 Smirnoff, 2000).

Flavonoids and Anthocyanins

Derivatives of the flavonols quercetin and kaempferol (Buer et al. 2010). Quercetin- and kaempferol-derivative flavonoids are usually glycosylated and frequently contain a hydroxy-cinnamic acid moiety esterified to one of the glycosyl groups (orthodihydroxy B-ring-substituted flavonoids) (Tattini et al. 2004). The flavonoids are ubiquitous molecules occurring in the vacuoles and cell walls of epidermal cells and in nonsecretory and glandular trichomes, and it has been assumed that they primarily have the function of attenuating the shorter solar wavelengths due to their good quantum efficiency (Burchard et al. 2000). In this way, the location of flavonoids in trichomes (Tattini et al. 2004) , cuticular wax layers (Fukuda et al. 2008), and epidermal cells (Burchard et al. 2000) may largely prevent that the UV-B radiation reaches sensitive targets within the leaf. However, the flavonoids also have another protective function against the shorter solar wavelengths. Considering that the...

Nutritional Strategies for Prevention

The fiber from wheat bran, for example, is deserving of special attention, as it may be able to decrease the risk of colon cancer via various mechanisms. One of the principal ways in which a high cereal fiber diet may be beneficial is by decreasing the amounts of secondary bile acids that are irritating to the colonic mucosa. In fact, at least one of these secondary bile acids, deoxycholic acid, increases the proliferation of colonic epithelial cells.12 Research has shown that these bile acids, including deoxycholic acid, were significantly reduced when subjects consumed 10 g per day of wheat bran, but not oat bran, as an addition to their typical Western diet.13 Also, intake of dietary carbohydrates, particularly from degradation-resistant starches and dietary fiber, are fermented in the colon and form short chain fatty acids (SCFA), primarily acetate, propionate, and butyrate. These SCFAs have been shown to decrease proliferation and migration in experimentally induced cancer cell...

The Mode Of Action Of Allelochemicals

Shikimate pathways, by natural elicitors such as fish protein hydrolysates (FPH), lactoferrin (LF) and oregano extract (OE). Elicitation significantly improved the phenolic, antioxidant and antimicrobial properties of mung bean sprouts. The optimal elicitor concentrations were 1 ml l FPH, 250 ppm LF and 1 ml l OE for the highest phenolic content that was approximately 20, 35 and 18 higher than control, respectively, on day 1 of dark germination. The antioxidant activity estimated by P-carotene assay in mung bean sprouts was highest on day 1 of germination for all treatments and control. in general, higher antioxidant activity was observed in the elicited sprouts compared with control. In the case of 1,1-diphenyl-2-picrythydrazyl (DPPH) assay the antioxidant activity for all treatments and control was highest on day 2. Among the different elicitor treatments, OE elicited mung bean sprouts showed the highest antioxidant activity of 49 DPPH inhibition on day 2. This increased activity...

Summary And Conclusions

Antioxidant and antiatherogenic properties of PJ, either directly (by measuring the size of the atherosclerotic lesions, or the extent of foam-cell formation), or indirectly (by measuring such parameters as the level of plasma lipoproteins, blood platelets, activities of various enzymes associated with oxidative stress, and gene expression). However, these studies provide little information about the phytochemical constituents responsible for the observed activities, or about the bioavailability of the suspected active agents. The instances in which specific components of PJ were tested involved in vitro experiments, and as such their contribution to an exploration of the role of specific molecules in pomegranate fruits is less significant. The tendency for this type of research (i.e., in which the in vivo effect of the whole fruit is investigated) to become dominant may have several explanations it is a relatively young field, giving it a higher chance of yielding positive results...

Better Use Of Existing Herbicides

Herbicide safeners are chemicals that reduce herbicide toxicity to crop plants via a physiological mechanism, usually by enhancing herbicide metabolism. They can be used to examine systemwide effects of an herbicide application on a target species. For example, Castro et al. t2005) treated grapevine with flumioxazin and found that thirtytthree distinct proteins had altered synthesis patterns compared with untreated plants. These proteins included a diverse range of functions including photosynthesis-related proteins and antioxidant systems, allowing an overview of the systemic effects of the herbicide application. Zhang and Reichers (2004) used a similar approach to examine the influence of the herbicide safener fluxofenim on the chloroacetamide herbicide dimethenamid in wheat. They found that the safener caused eighteen proteins to be induced, including fifteen glutathione - S - transferase (GST) subunits and three proteins with known roles in glycolysis and the Krebs cycle....

Abiotic Stresses and ROS in Crop Plants

ROS are free radicals of oxygen that are chemically active. Presence of unpaired electrons in the valence shell of these molecules renders them highly reactive, resulting in damage of cell structure and function. Plant cells continuously produce ROS even under normal condition, since they play an important role in cell signalling, but when produced in excess leads to oxidative stress. Plants maintain a steady state balance between ROS production and anti-oxidant defence mechanism under normal condition, but various abiotic

Stress and Redox Metabolism

Plants are submitted to a wide variety of environmental stresses, like high light, drought, nutrient deficiency, and temperature that can induce oxidative stress. In addition, intermediates in electron transfer reactions may react with other cell constituents and produce radicals and reactive oxygen species. Reactive oxygen species are responsible for major damages to membrane lipids and proteins. Consequently, an efficient antioxidant network is essential for protecting cell functions, particularly in chloroplasts. A whole set of metabolites such as glutathione and ascorbate, carotenoids, tocopherols, and enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione peroxidase are known elements of antioxidant metabolism (for review, see Mullineaux and Karpinski 2002). The presence of a-tocopherol and xanthophylls in envelope membranes (see above) is a first element for this system to play a role in oxidative stress responses. Furthermore, several proteins...

Salt Tolerance Mechanisms

Regarding antioxidant metabolism, among different species, there is an induction of the antioxidant system under saline conditions and in response to the imbalance between the supply and demand of NADPH and the possible generation of ROS. In the case of A. tripolium (Geissler et al. 2009a, 2010), the plants seemed to use more energy supply under elevated CO2 than under ambient CO2 concentrations for increasing the investment in antioxidant metabolism. In this case, the SOD and APX activities resulting from salt treatment were significantly enhanced under elevated CO2 as compared with their counterparts under ambient CO2 (Table 3), so that ROS could be scavenged more effectively. However, in H. vulgare (Perez-Lopez et al. 2009b, 2010b), although salinity caused lessened oxidative damage, measured as solute leakage (Table 3), a reduced upregulation of the antioxidant system at elevated CO2 compared to ambient CO2 was observed. This trend was also detected in tomato for CAT activity...

The Role Of Cell Organelles In Hr Induction

Strengthened by the observation that the HR phenotype of several Arabidopsis lesion-mimic mutants, including lsdl and lsd3, is suppressed under short-day conditions (Dietrich et al., 1994). Likewise, catalase-deficient tobacco plants exposed to high light intensities developed necrotic lesions, which may be caused by excess ROI produced by chloroplast metabolism (Chamnongpol et al., 1996). In agreement with the assumption that perturbation of photosynthesis or other chloroplast functions may induce HR-like cell death is the recent characterization of the Arabidopsis ACD2 gene, which encodes a red chlorophyll catabolite reductase (Mach et al., 2001). It has been suggested that the cell death phenotype of acd2 mutant plants is caused by the accumulation of chlorophyll breakdown products, which might be specific triggers of cell death or might function by their ability to absorb light and generate free radicals (Mach et al., 2001). Recently, the plastid-localized protein DS9 was shown to...

Types of Chemical Defenses

The most diverse and common secondary compounds are phenolics. Defined by possessing a benzene ring with one attached hydroxyl, an enormous number of structures can be called phenolic. Most of the more than twenty-five thousand known types of phenolics are good antioxidants and are frequently used as preservatives in plants they prevent membrane oxidation and other types of oxidative damage. As defenses, various phe-nolics are distasteful, toxic, and inhibit digestion. When activated by light, coumarins in such plants as carrots and celery cross-link deoxyribonucleic acid (DNA) strands and halt cell division. The blue and red colors of most antioxidant a substance that prevents damage from oxygen or other reactive substances Glucosinolates. Glucosinolates comprise a small (one hundred) group of compounds containing both nitrogen and sulfur. They, too, are good antioxidants, but they are best known as repellents. They occur primarily in the cabbage family, where they provide...

H2O2 Scavenging Catalases and Ascorbate Peroxidases

Ascorbate peroxidases are class I heme peroxidases important in H2O2 scavenging, of which eight types are expressed in Arabidopsis thaliana three cytosolic (APX1, APX2 and APX6), two chloroplastic (stromal APX and thylakoid APX) and three microsomal types (APX3, APX4 and APX5) (Panchuk et al. 2002). This enables a crucial cross-compartment protection since H2O2 is transported across biological membranes (Davletova et al. 2005a). APXs catalyse the reduction of H2O2 to H2O and O2 using AsA as a reducing agent in the AsA-GSH cycle (Fig. 2, cfr. infra), connecting enzymatic antioxidant systems with antioxidant metabolites.

Human Use of Defensive Chemicals

The nervous system activity of some alkaloids has been exploited for recreational and religious drug use (opium, cocaine, nicotine, caffeine, and mescaline) and medicine (opium and codeine). The ability of some to block signal transmission at neuromuscular junctions makes them important in surgery as well as hunting tools (e.g., curare). Polyphenols have broad antimicrobial activity they inhibit oxidative enzymes (e.g., cyclooxygenases) that cause disease, and their antioxidant characteristics are thought to prevent aging and some cancers. Much the same has been claimed for glucosinolates (cabbage family). More than 90 percent of the medicines prescribed in the twentieth century were originally plant derived, mostly involving presumed defensive chemicals. Human medicinal use of plants is based almost entirely on the action of defensive chemicals.

Antioxidative Properties Of The Pomegranate Tree Parts

Since pomegranate tree parts may also contain polyphenols with antioxidant activ-ity,57 we have prepared ethanolic extracts of whole crude pomegranate plant parts. The polyphenol concentrations in these extracts decreased in the following order bark stem whole fruit juice leaves. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging capacity assay, using similar total polyphenol content (10 pmol of total polyphenols L) from each of the pomegranate tree parts, the following order of potency was observed bark whole fruit juice stem leaves. Analysis of the antioxidant activity against copper ion-induced LDL oxidation, using similar total polyphenol concentrations, revealed a dose-dependent inhibition of LDL oxidation. These results suggest that different polyphenolic flavonoids are present in the pomegranate tree parts and, hence, on using total polyphenol content, specific flavonoids exert different antioxidative potency. The pomegranate flower powder ethanolic extract...

The Latest Stage of Nodulation Nodule Senescence

Besides hormones, ROS are also important in nodule senescence. Several reports demonstrate a decrease in antioxidant enzymes and in ascorbate and glu-tathione during nodule senescence. Differences in ROS levels seem to be more variable depending on nodule type, legume species or experimental conditions. Several hypotheses have been proposed but more experimental data are needed to elucidate the role of ROS during nodule senescence (Puppo et al. 2005).

Enzymatic Components of the ROSScavenging Pathways of Plants

Major ROS-scavenging enzymes of plants include superoxide dismutase (SOD), ascorbate peroxi-dase (APX), catalase (CAT), glutathione peroxidase (GPX), and peroxiredoxin (PrxR). Together with the antioxidants ascorbic acid and glutathi-one, these enzymes provide cells with highly efficient machinery for detoxifying O-- and H2O2. The balance between SODs and the different H2O2- scavenging enzymes in cells is considered to be crucial in determining the steady-state level of O2- and H2O2 (Romero-Puertas et al. 2006). This balance, together with the sequestering of metal ions by ferritin and other metal-binding proteins, prevents the formation of the highly toxic HO- radical via the metal-dependent HaberWeiss reaction or the Fenton reaction. The cellular pools of the antioxidants ascorbic acid and glutathione are maintained in their reduced state by a set of enzymes capable of using NAD(P)H to regenerate oxidized glutathione or ascorbic acid (e.g. mono-DHAR, DHAR, and GR). DHARs and...

Antioxidative Properties Of The Pomegranate Fruit Fractions

The antioxidant activities of the whole pomegranate fruit and its anthocyanidins (delphinidin, cyanidin, and pelargonidin) extracts were studied.58 Pomegranate fruit extract exhibited scavenging activity against hydroxyl radicals and superoxide anions, and this effect could be related to the fruit anthocyanidins. The IC50 (the concentration needed to get 50 inhibition) values for superoxide anion scavenging capacity of delphinidin, cyanidin, and pelargonidin were 2, 22, and 456 pmol L, respectively. The above anthocyanidins did not effectively scavenge NO radical, but inhibited H2O2-induced lipid peroxidation in rat brain homogenates, with IC50 values of 0.7, 3.5, and 85 pmol L for delphinidin, cyanidin, and pelargonidin, respectively.58 We compared the various pomegranate fruit constituents aril juice, skin (red), membrane (white), and seeds. All these parts of the fruit contain polyphenols, with the highest concentration observed in the membrane fraction and the lowest concentration...

Antioxidative Capacity Of Pomegranate Juice In Comparison To Other Juices

Pomegranate juice was shown to possess an antioxidant activity that was three times higher than the antioxidant activity of green tea.63 The antioxidant activity was higher in juice extracted from whole pomegranate than that of juice obtained from arils only, suggesting that the processing extracts some of the hydrolyzable tannins present in the fruit rind into the juice. We have demonstrated that pomegranate juice contains a higher concentration of total polyphenols (5 mmol L) in comparison to other fruit juices (orange, grapefruit, grape, cranberry, pear, pineapple, apple, and peach juices, which contain only 1.3 to 4 mmol L of total polyphenols, Table 2.1). A similar pattern was noted for IC50 values, obtained for the inhibition of copper ion-induced LDL oxidation. While PJ exhibited a very low IC50 (0.06 l mL), the IC50 values for the other juices were in the range of 0.11 to 7.50 l mL (Table 2.1). The most potent antioxidant activity of PJ could be related to its high...

An Integrated View of Photoprotection

Demmig-Adams et al., 1998, this volume). For both of these scenarios, the capacity for detoxification of reactive oxygen species and other radicals is likely to be limited due to either low levels of antioxidants (shade-acclimated leaves) or an inhibition of the activity of enzymatic antioxidants by the low temperatures. On the other hand, under conditions of limiting nutrients (Verhoeven et al., 1997 Logan et al., 1999 Morales et al., this volume), and low water availability and or high temperatures (Barker et al., 2002), photosynthesis can be downregulated, and zea-xanthin retained nocturnally, but without being maintained in an engaged state primed for thermal energy dissipation. Instead, the retained zeaxanthin remains poised for engagement (presumably upon protonation of the PsbS protein) and can thus respond more rapidly than if violaxanthin had to first be enzymatically converted to zeaxanthin, yet the system maintains complete flexibility in terms of engagement and...

Antioxidative Potency Of Fractions Isolated From Pomegranate Juice

The PJ hydrolyzable tannins are punicalin, pedunculagin, punicalagin, and gal-lagic and ellagic acidesters of glucose.65 We demonstrated that punicalagin inhibited copper ion-induced LDL oxidation and this effect could be related to its capability to scavenge free radicals. Punicalagin also reduced macrophage oxidative stress by up to 90 , and the ability of the cells to oxidize LDL by up to 40 .

Metabolism In Plant Cells Under Stress Reactive Oxygen Species

Molecular oxygen dioxygen) has the unusual chemical property that it has two unpaired electrons with parallel spins. The ground-state oxygen molecule is triplet and excitation by energy transfer leads to highly reactive singlet state oxygen (singlet oxygen). The particular chemistry of oxygen also means that an univalent reduction (by accepting one single electron) is probable. This reaction yields oxygen free radicals. Free radicals are molecules with one unpaired electron, many of them very reactive. In the redox interconversion chain from 02 to H20 which requires a total of 4 electrons per 02 molecule several intermediates (ROS ) exist. All of them are less stable than 02 or water. Reactive oxygen species include the superoxide anion free radical (02 *), the hydroxyl free radical (OH*), hydrogen peroxide (H202) or the singlet oxygen. Oxidative attack initiates lipid peroxidation, protein oxidation, DNA damages, and pigment bleaching (Elstner and OBwald 1994). of peroxidases....

Miscllaneous compounds

Isoflavones are found in Glycine max (soybean). Clinical research has demonstrated soy isoflavones to be effective in menstrual diseases. They also have an antioxidant activity . Isoflavones belong to a group of compounds known as phyto-estrogens. The isoflavone content of soybean is 10 to 20 times more than other plants. Genistein is a potent tyrosine inhibitor, where as daidezein also has an antioxidant activity (Fig. 5.255). Recently isoflavones have been investigated for hypolipidemic activity.

As Developmental Regulators

Flavonoids are, in fact, well-known endogenous regulators of auxin movement (Jacobs and Rubery 1988 Brown et al. 2001 Peer and Murphy 2007), and, interestingly, antioxidant fla-vonoids display the greatest ability to regulate the transport of auxin in vivo (Taylor and Grotewold 2005 Besseau et al. 2007). Quercetin aglycone (which lacks the glycosyl moiety in the 3-postion of the flavonoid skeleton, and hence, display the greatest antioxidant potential, Rice-Evans et al. 1996) is more effective than both kaempferol aglycone and quercetin 3-O-rutinoside to inhibiting the basipetal transport of auxin (PAT, Jacobs and Rubery 1988 Besseau et al. 2007). Flavonoids may profoundly alter the tissue- and cell-specific auxin concentrations by tightly affecting the IAA-oxidation (Mathesius 2001), not just by modulating its intra- and intercellular movements. Monohydroxy B-ring flavonoids have long been shown to behave as cofactors and dihydroxy B-ring flavonoids as inhibitors of the...

Metabolic Engineering

To cope up with different abiotic stresses plants alter their metabolic pathways to adjust to changed environments (Rathinasabapathi, 2000). The metabolic pathways such as proline, glycinebetaine, polyols, antioxidant components become more active to keep the plant survive under stress conditions. However, the initiation and efficiency

Health aspects of carotenoids

In human nutrition, carotenoids play an important role as a source of provitamin A. In the gastrointestinal tract 3-carotene gets converted to vitamin A, which plays an important role in the regulation of vision, growth and reproduction (Ong and Choo, 1997). More recently, however, the protective effects of carotenoids against serious disorders such as cancer (Peto et al., 1981 Shekelle et al., 1981), heart disease, squamous cell carcinoma of the lung, oral tumours and degenerative eye disease have been recognized, and have stimulated intensive research into the role of carotenoids as antioxidants and as regulators of the immune response system. The antioxidant property of 3-carotene by its effective radical trapping was studied by Burton and Ingold (1984). Kunert and Tappel (1983) reported the efficient reduction of lipid peroxidation by prior treatment with 3-carotene in guinea pigs.

Proteome To Cope With Environmental Stresses

Environmental stresses, including biotic and abiotic stresses such as pathogen infection, salinity, drought, herbicide and heavy metals, are important factors that affect growth and metabolism of plants. To cope with environment stresses, plants can change their gene expression and protein accumulation 19 . One of the most common consequences of stresses is ample production of ROS and, eventually, oxidative stress 20 . To counteract the harmful effects of oxidative stress, plant cells develop an antioxidant defense system for redox balance 21 . Information from proteomics analysis of plant roots in response to biotic and abiotic stresses reveals many proteins involved in ROS metabolism. A set of antioxidant enzymes was identified under different stress conditions. For example, up-regulation of POX was induced by salt stress three SODs, two GPX, one peroxiredoxin, and one -benzoquinone reductase were up-regulated by As treatment three GSTs were abundant under Cd stress and four...

Extraction and downstream processing of pungency principles and pigments of Capsicum

Provitamin-A carotenoids of Capsicum, namely 3-carotene and 3-cryptoxanthin, are reduced during the processing of paprika. Esterified carotenoids, which are found as ketocarotenoids, cap-santhin and capsorubin, are more stable than zeaxanthin (free, monoesterified and diesterified forms), 3-cyrptoxanthin (free and mono-esterified form) and 3-carotene (free form) (Howard, 2001). Loss of provitamin-A activity of 67 and 81 has been reported for paprika varieties Agridulce and Bola, respectively. (Minguez-Mosquera and Horneo-Mindez, 1994). The natural antioxidants present in the fruit prevent the degradation of colour (Kanner et al., 1979). Tocoferol acts as an oxidation barrier, while ascorbic acid is useful for tocoferol regeneration and carotenoids prevent lipid oxidation (Esterbauer, 1991). Though there are reports of a decrease of capsaicinoid upon food processing, the pungency factor is generally not affected under the conditions of oleo-resin preparation. However, prolonged storage...

Leaf Senescence and Proteomics

Studying leaf senescence with proteomics is just at the initial phase. Using TEM, Wilson et al. 26 observed that the most obvious ultrastructural changes during senescence occurred in chloroplasts of white clover leaves with progressive loss of thylakoid integrity and accumulation of osmiophilic globules in the stroma. The leaf proteins were separated by 2-DGE and verified by MALDI-TOF-MS. Out of 590 2D gel spots, 40 of them showed significant senescence-related changes in abundance. Moreover, approximately one-third of those senescence-responsive spots with decreased abundance appeared in the 2D gel profiles of the isolated chloroplasts. TMS analysis demonstrated those spots to be chloroplast proteins, including RuBisCO LSU and SSU, a RuBisCO activase, glutamine synthetase, and the 33-kDa protein of the PS II OEC. Since those proteins are key elements in photosynthesis, the decline in their expression levels emphasized the importance of proteolysis, chloroplast degradation, and...

Ferric Reductase And Ferritin

Into Fe-free growth medium is required to deplete Fe stores in rhizobia. This storage of Fe in rhizobia could be attributed to the presence of either ferritin or bacterioferritin (Andrews, 1998). In highly aerated cultures growing in an Fe rich medium, bacteria will acquire and store Fe in these unique structures. While the ferritin in bacteria is remarkably similar to eukaryotic ferritin, bacterioferritin has a heme moiety attached to the subunits making up the ferritin structure. An obvious function of ferritin in bacteria is to deplete free ionic Fe from the cytoplasm and store it as ferric ion in specific Fe-containing molecular structures. It is not desirable for free Fe3+ to be present in the cytoplasm because interaction with O2 could result in the formation of highly toxic free radicals. A role of the heme groups attached to the ferritin unit in bacteria is to aid in the oxidation-reduction reactions moving Fe into and out of ferritin. An additional role of bacterioferritin...

Plant Mechanisms to Cope with Cadmium

Enters first by the roots through the cortical tissue. Roots accumulate Cd during its exposure and part of the metal is then translocated to leaves (Ogawa et al. 2009). Cd can be loaded rapidly into the xylem by transport to the above-ground tissues. Once Cd has entered into the cytosol, it can bind to phytochelatins or their precursor glutathione, generating conjugates that can be transported into the vacuoles, preventing the free circulation of Cd ions in the cytosol (Cobbett 2000 Verbruggen et al. 2009). Cd can also be complexated by metallothioneins and nicotianamine (Cobbett and Goldsbrough 2002 Sharma and Dietz 2006). Proline, histidine and polyamines are also involved in the defence against metal stress because they may be involved in osmoregulation and metal chelation, or they can act as antioxidants (Sharma and Dietz 2006). Referring to compartmen-talisation of Cd, it has been shown that some of the genes regulated by Cd are involved in its own transport, like AtPcrl (Song et...

Iron And Oxygen Toxicity

Bacteroids is required to provide the 15-18 ATP for each N2 molecule fixed however, oxygen toxicity is an additional concern and bacterial systems usually have an elaborate system involving oxygen stress response. Thus, there is the paradox in the nodule of having sufficient O2 but not having an excess which would be both inhibitory for gene expression or enzyme structure and toxicity attributed to the formation of free radicals. A consequence of Fe3+ presence is the interaction with molecular oxygen to produce toxic free radicals. The catecholate siderophores of Azotobacter vinelandii are important in management of oxidative stress because protochelin and azotochelin, but not aminochelin, were able to prevent the generation of the hydroxyl free radical by a series of reactions involving free Fe3+ (Cornish and Page, 1998). Reactions leading to hydro xyl radical formation are as follows The low binding affinity of aminochelin for Fe3+ is reflected by the ligand Fe3+ ratio for...

The end product of nitrate assimilation is a whole spectrum of amino acids

Proline protects a plant against dehydration, because, in contrast to inorganic salts, it has no inhibitory effect on enzymes even at very high concentrations. Therefore proline is classified as a compatible solute. Other compatible solutes, formed in certain plants in response to water stress, are sugar alcohols such as mannitol (Fig. 10.13), and betains, consisting of amino acids, such as proline, glycine, and alanine, of which the amino groups are methylated. The latter are termed proline, glycine, and alanine betains. The accumulation of such compatible solutes, especially in the cytosol, chloroplasts, and mitochondria, minimizes the damaging effects of water shortage or high salt content of the soil. These compounds also participate as antioxidants in the elimination of reactive oxygen species (ROS) (section 3.9). Water shortage and high salt content of the soil causes an inhibition of CO2 assimilation, resulting in an overreduction of photosynthetic electron transport carriers,...

Conclusions and Future Research Directions

Peroxidation and the presence of detectable amounts of H2O2. However, the combined action of energy dissipation processes, antioxidants, and antioxidant enzymatic systems in water stressed, nutrient-limited, and salinity-affected plants seems to maintain a large part of PS II undamaged, and in most cases there is no evidence for major sustained photodamage under such environmental conditions. In general, the concentrations of most oxidative defense components tend to increase with the stress when they are expressed on a basis that considers the capacity to produce reactive oxygen species (i.e. on a chlorophyll basis). In any case, oxidative stress-related processes, which are traditionally regarded as damage, could also be re-interpreted as part of the redox-regulated signal transduction pathways (Demmig-Adams and Adams, 2003). Future research should be focused to investigate these systems in plants under limited nutrient or water availability.

Conclusions and Future Prospects

The carotenoid biosynthetic pathway is now well understood. The major challenge is to provide insight into the regulatory aspects of carotenoid biosynthesis during nuclear transcription, protein translocation, plastid biogenesis and plant development. Understanding needs to be improved of how phytohormones, abiotic stress and metabolic feedback affect carotenoid composition and regulation. As knowledge of the regulatory processes increases, researchers will be able to make informed decisions about the effects of manipulating the pathway. This will allow the development of the next generation of crops which enhance and build upon the benefits of 'Golden Rice'. The result could entail significant health benefits for society by providing essential antioxidant micronutrients and vitamin A derivatives. As the health benefits from these crops can be obtained by changing the composition of foods already eaten without altering the eating habits of the consumer, they will have a much greater...

ROS Metabolism in Response to Cadmium 51 ROS Production Under Cd Stress

Reactive oxygen species (ROS) such as O2 OH or H2O2 are produced as a result of normal aerobic metabolism (Gutteridge and Halliwell 2000). An excess of ROS, however, is dangerous for the plant, mainly due to the reaction with lipids, proteins and nucleic acids giving rise to lipid peroxidation, membrane leakage, enzyme inactivation and DNA break or mutations, which can induce severe damage to the cell (Halliwell and Gutteridge 1999). Although Cd2+ is not able to directly generate ROS by a Fenton reaction, it might inhibit antioxidant enzymes, impair the respiratory chain, or displace copper and iron ions in metalloproteins, which eventually trigger a Fenton reaction (Valko et al. 2005). It has been reported that Cd produces concentration-dependent imbalances in the antioxidant defence of plants and induces oxidative stress (Romero-Puertas et al. 1999 Dixit et al. 2001 Sandalio et al. 2001). Additionally, ROS production at subcellular levels was demonstrated in plants grown under Cd...

Metallomics And Metallomes

Transgenic plants with modified genes of PCS and genes of glutathione synthesis enzymes, a-GCS and GS, and enzymes connected with sulphur metabolism, e.g., serineacetyltransferase, need special attention in order to achieve success in phytoremediation of metals in the environment. Plants under heavy metal stress produce free radicals and reactive oxygen species and must withstand the oxidative stress before acquiring tolerance to toxic metals. Glutathione is then used for the synthesis of PCs as well as for dithiol (GSSG) production. The ascorbate-glutathione pathway is involved in plant defense against oxidative stress. Organic acids play a major role in metal tolerance 8 .