How to Detoxify Your Body Naturally

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Detoxifying Processes

Detoxification Pathway Dysfunctions the urine (kidneys) and feces (liver and intestines). The skin and lungs provide ancillary support for these processes. Neutralization occurs via a series of complex processes by which toxic chemicals are metabolized to either inert or more readily excreted substances until elimination occurs. When detoxification pathways fail, toxins may accumulate in body tissues, most frequently in fat tissue. This situation emphasizes the importance of nutrient support for antioxidant functioning and detoxification processes for any patient who is experiencing rapid weight loss, when that patient's fat tissues release their toxic loads. The liver is, without question, the leading detoxification organ. On the macroscopic level, the liver filters 2 liters of blood per minute, filtering out large toxins. The liver synthesizes bile and cholesterol that help to bind fat-soluble toxins for excretion. On the microscopic level, this organ neutralizes chemical...

Phase 2 Detoxification

Phase 2 detoxification can be broken down into well-defined detoxification pathways, each with unique abilities for addressing certain toxin categories. Phase 2 detoxification occurs principally via the pathways of acetylation, amino acid conjugation, glucuronidation, glutathione conjugation, methylation, sulfation, and sulfoxidation. Table 9-3. Phase 1 and Phase 2 Detoxification Modulators3

Supporting Detoxification Within The Body

Using this overview and framework of principal mechanisms of liver detoxification, it is wise to focus on essentials for therapeutic intervention, ensuring that the proper balance between phases 1 and 2 detoxification stages is maintained. It is believed that up to 90 of cancer cases arise from the effects of exposure to environmental chemicals, such as those found in air pollution, tobacco, chemically contaminated food, and antimetabolites that deplete nutrients that are essential for proper detoxifyication.16,17 Therefore, choosing nutrients and botanical medicines to support detoxification can improve quality of life, alleviate acute signs and symptoms of excess toxic load, and confer protection over the course of a patient's life. The next sections cover key botanicals, nutrients, and dietary constituents that represent potential clinical interventions for treating acute or chronic cases of toxicity, depending on each patient's condition. This common herb, used frequently in the...

Symptoms That Suggest Detoxification Imbalance

Numerous tests can be conducted to measure liver detoxification functioning. Measurement of metabolite levels before and after challenges with acetaminophen, caffeine, or other chemicals can provide detailed information about an individual's detoxification functions. Testing for phase 1 and phase 2 enzyme polymorphisms are also available and are able to predict susceptibilities to toxic overload. There are, however, a number of readily observable signs that suggest that an individual may have overactive or underactive detoxification functions. Table 9-2 on page 109 summarizes some of the more commonly noted detoxification pathway dysfunctions and their symptoms.

Physicochemical Restriction in Detoxification Process visvis Choice for Getting Rid of Excess Heavy Metal Ions

The redox potential is an important criterion for detoxification by reduction. The redox potential of a given heavy metal should be between the hydrogen-proton couple (0 V) and the oxygen-hydrogen couple (1.229 V) 10 , which is the physiological redox range for most aerobic cells. Thus, Hg2+ (0.851 V) chromate (1.350 V) arsenate (0.560 V) and Cu2+ (0.153 V) may be reduced by the cell, but Zn2+ (-0.762 V) Cd2+ (-0.4030 V) Co2+ (-0.28 V) and Ni2+ (-0.257 V) may not 10 . The second constraint arises in the context of scavenging the reduced product. The reduced product should be able to diffuse out of the cell or it might reoxidize itself. In fact, most reduction products are quite insoluble (Cr3+) or even more toxic (AsO2) than the educts. Logically, even if the cell decides to detoxify a compound like that by reduction, an efflux system should be present to push off the reduced products to the environment. Only in case of mercury do reducibility and a low vapor pressure of the metallic...

Role Of Pcs In Detoxification Of Heavy Metals Other Than Cadmium

Because plants assimilate various metal ions from soil, the first organ exposed to these ions is the root. Localization of PC synthetase to roots and stems probably provides an effective means of restricting the heavy metals to these organs by chelation in the form of Cd-PC complexes. It has been demonstrated that PCs are able to protect enzymes from heavy metal poisoning in vitro 65,132 many metal-sensitive plant enzymes (rubisco, nitrate reductase, alcohol dehydrogenase, glycerol-3-phosphate dehydrogenase, and urease) were more tolerant to Cd in the form of a Cd-PC complex compared with the free metal ion. Free PCs could reactivate the metal-poisoned enzymes (nitrate reductase poisoned by Cd-acetate) in vitro more effectively than other chelators such as GSH or citrate 65 .

Cell Biology and Biochemistry of ROSProducing and ROSDetoxifying Systems and Their Relation to Water Deficit

ROS-detoxifying mechanisms are a prerequisite of organisms to survive in an oxygen-containing environment as ROS production is inevitably a component of an aerobic metabolism. A large number not only of original papers but also of reviews have been published addressing generation and detoxification of ROS (e.g., Smirnoff 1993 Buchanan and Balmer 2005 Apel and Hirt 2004 Mittler 2002 Mittler et al. 2004 Zimmermann and Zentgraf 2005 Van Breusegem et al. 2008 Dietz 2005 Foyer and Noctor 2005a, b Vieira Dos Santos and Rey 2006), and many of them emphasize the connection between ROS and abiotic stress like drought (Smirnoff 1993 Mittler 2006 Chen et al. 2004 Jaspers and Kangasjarvi 2010 Dat et al. 2000 Cruz de Carvalho 2008 Reddy et al. 2004 Miller et al. 2008). In view of this widespread knowledge, we do not expand on the basics of ROS biochemistry but rather address some special aspects of cell biology related to drought and desiccation. ROS-generating and ROS-scavenging reactions are...

Detoxification Of Electrophilic Xenobiotics

The mechanism of detoxification is conjugation between the xenobiotic at its electrophilic site and the thio-group of glutathione. This conjugation reaction will proceed spontaneously with a large number of electrophilic xenobi-otics of similar softness. The reaction with hard electrophiles requires additional enzymatic support, which is provided by glutathione S-transferase isoenzymes. In any case detoxification totally depends on the availability of glutathione. The homeostasis of glutathione inside the plant is maintained by a complex regulation process (see other chapters of this volume) with synthesis, degradation and long range transport as visible end points. Perturbation of homeostasis and depletion of GSH pools may therefore lead to severe disturbance in a plant's detoxification capacity. Prerequisites for glutathione dependent detoxification

Xenobiotics are detoxified by conjugation

Toxic compounds produced by the plant or which are taken up (xenobi-otics, including herbicides) are detoxified by reaction with glutathione. Catalyzed by glutathione- transferases, the reactive SH group of glutath-ione can form a thioether by reacting with electrophilic carbon double bonds, carbonyl groups, and other reactive groups. Glutathione conjugates (Fig. 12.6) synthesized in this way in the cytosol are transported into the vacuole by a specific glutathione translocator against a concentration gradient. In contrast to the transport processes, where metabolite transport against a gradient proceeds by secondary active transport, the uptake of glutathione conjugates into the vacuole proceeds by an ATP-driven primary active transport (Fig. 1.20). This translocator belongs to the superfamily of the ABC-transporter (ATP binding cassette), which is ubiquitous in plants and animals and is also present in bacteria. Various ABC transporters with different specificities are localized in...

Phase 1 Detoxification

In general, phase 1 detoxification arises from the function of a group of some 50-100 enzymes referred to as cytochrome P450. The healthy functioning of this pathway depends upon an individual's nutritional status, genetics, and level of exposure to chemical toxins. Thus, an individual's risks of developing disease states arising from insufficient detoxification varies greatly. Indeed, this can explain the great variability in patients' susceptibility to, and manifestation of, disease processes such as cancer from environmental pollutants, such as smoking. Clinical evaluation of a patient's risk entails a twofold consideration (1) that of total toxin load and (2) that of his or her ability to process the exposure. Phase 1 detoxification becomes less active with aging. Complicating this decreased function is that blood flow through the liver also diminishes with age. Not surprisingly, there is an increased susceptibility to adverse drug reactions among older adults, whose...

Antioxidant Defence for Abiotic Stress Tolerance

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 tobacco glutathione-S-transferase (GST) and glutathione peroxidase (GPX) reduced oxidative damage in the stressed transgenic seedlings (Roxas et al. 2000). Furthermore, overexpression of CuZn superoxide dismutase (SOD) and ascorbate peroxidase (APX) in transgenic sweet potato enhanced tolerance and recovery from drought stress. This was due to a considerable increase in expression of antioxidant enzymes that reduced the levels of...

Involvement of Other Novel Genes Like MicroRNA in Plant Stress Tolerance

Sunkar et al. (2006) provided evidence on involvement of miRNA in oxidative stress responses by targeting cytosolic and chloroplas-tic superoxide dismutases that detoxify superoxide radicals. Transcript expression of miR398 in response to oxidative stress was down-regulated, leading to posttranscriptional accumulation of the SOD mRNA and thus oxidative stress tolerance. Moreover, transgenic Arabidopsis plants overexpressing a miR398-resistant form of SOD accumulated more mRNA than plants overex-pressing a regular form and were consequently much more tolerant to high light, heavy metals and other oxidative stresses. Arabidopsis have been shown to trigger the accumulation of

Secondary Metabolites

Many secondary metabolites are highly toxic to insects. In order to exploit plant tissue containing secondary metabolites insects have evolved behavioral adaptations to avoid the chemicals (Dussourd 1993), or efficient detoxification systems (Brattsten 1992). Presumably, biochemical adaptations are costly (Berenbaum and Zangerl 1992b) and have been considered to be the prime reason for the widespread specificity in plant use among herbivorous insects. For example, 16 out of 72 needle-eating insect species on Scots pine Pinus sylvestris in Sweden feed only on the genus Pinus (Bj rkman and Larsson 1991). However, other phenomena, e.g., escape from natural enemies, also are likely to contribute to the high degree of host plant specialization in herbivorous insects (Bernays and Graham 1988 Stamp 2001).

Nonenzymatic Antioxidants 331 Ascorbic Acid

And nonenzymatic reactions and is thus a powerful radical scavenger. It can directly scavenge 1 O2, O2 and -OH radicals produced in the cell and can protect membranes against oxidative stress. In plant cells, the most important reducing substrate for H2O2 detoxification is ascorbic acid (Turkan et al. 2005). An increase in oxidized ascorbate during Cd stress has been reported by Demirevska-Kepova et al. (2006) in Hordeum vulgare. Yang et al. (2008) also reported that drought stress increases the ascorbate content in Picea asperata. Water stress results in significant increases in antioxidant AsA concentration in turfgrass (Zhang and Schmidt 2000 Vranova et al. 2002 Jaleel et al. 2007). Ascorbic acid shows a reduction under drought stress in maize and wheat, suggesting its vital involvement in oxidative response (Vertovec et al. 2001 Nayyar and Gupta 2006). In contrast to the studies mentioned earlier, in some cases antioxidant activities are enhanced by elevated CO2. In ozone stressed...

Distribution of Heavy Metals and Conjugating Ligands in Root

The increase of the cell walls (CWs) capacity to bind Pb by formation of cell wall thickenings (CWTs) rich in JIM5 pectins, callose and lipids in Funaria hygrometrica plant cells treated with Pb might be regarded as the next step in the development of the plant resistance strategy against this metal based on immobilizing toxic ions within apoplast (Krzeslowska et al. 2009). Binding metal ions within CWs is the important resistance strategy of plant cells in response to Cd (Fig. 1). This has been shown recently for T. caerulescens (Wojcik et al. 2005) Salix viminalis (Vollenweider et al. 2006) and Linum usitatissimum (Douchiche et al. 2007, 2010). In the last named, it was found moreover that exposing plants to Cd resulted in significant increases of both the cell wall thickness and JIM5 pectins formation level in CWs (Douchiche et al. 2007). In S. viminalis, the main Cd sink was pectin-rich collenchyma CWs of the veins. Moreover, also in this case, the amount of pectins slightly...

Distribution of Heavy Metals and Conjugating Ligands in Shoots

(e.g., Pb and As), Cd has a higher propensity to accumulate in shoots other than the roots. Still, there is normally more Cd in roots than in leaves, and even less in fruits and seeds (Wagner 1993). The tendency of tobacco plants to translocate Cd quite efficiently to the leaves contributes to the fact that tobacco smoke is an important Cd source for smokers (Lugon Moulin et al. 2004). But recently, some research showed that tobacco develops an original mechanism of metal detoxification by the exudation of metal Ca-containing particles through leaf trichomes (Choi et al. 2001 Choi and Harada 2005 Sarret et al. 2006).

Heavy Metal Perception in a Microscale Environment A Model System Using High Doses of Pollutants

Abstract The characterization of the mechanisms of heavy metal detoxification has been undertaken through several experimental approaches, where high metal concentrations have been frequently used. A microscale hydroponic system was used to discriminate between the direct and indirect phytotoxic effects that may occur under heavy metal stress at short exposure times. Induction of oxidative stress and generation of stress signaling molecules are some of the physiological responses triggered soon after the exposure of plant cells to heavy metals, which might be part of stress perception mechanisms. The generation of reactive oxygen species, in particular H2O2, ethylene or jasmonate are envisaged as messengers in signaling pathways that may result ultimately in cell senescence and growth inhibition.

Compartmentalized and Interconnected Metabolic Route

The detoxification of 2-PG and its recycling to 3-PGA occurs by the complex photosynthetic carbon oxidation cycle 125, 150 . Because this pathway leads to the consumption of oxygen (oxygenation of RuBP) and production of carbon dioxide (during the recycling of 2-PG) in the light, it is also called photorespiration. The specificity factor of the bifunctional enzyme Rubisco for the carboxylation reaction versus the oxygenation reaction is in the range of 80-100 for most land plants 137 .

Twoelectron reactions

These reactions are important detoxification mechanisms of toxic products produced by plants or xenobiotics. Furthermore, they reflect the ability of conjugated carbonyls to inactivate low-molecular weight and protein thiols in biological systems. The equilibrium constants as well as the rate constants for forward and reverse reaction are extremely dependent on the carbonyl structure, e.g. the mother compound acrolein reacts more rapidly than any other carbonyl to give very stable ad-ducts (half-lives for reverse reaction 4.6 days). 4-Hydroxy-2-alkenals, which derive from polyunsaturated fatty acids, are somewhat less reactive forming also very stable adducts showing half-lives between 3.4 and 19 days. Thus, the biological activity of aldehydic lipid peroxidation products is primarily determined by the reactivity of conjugated carbonyls towards thiol groups and due to the stability of the adducts (Esterbauer et al. 1975). Glutathione -transferases, which...

Enlightening the Mechanisms of Photoinhibition in Chlamydomonas reinhardtii

And NPQ photoprotection are called into question because mutants achieve maximum growth in VHL irrespective of whether the high DES is or is not expressed as NPQ (Forster et al., 2001). Evidently the 5 x slower PS II electron transfer in mutants from herbicide resistant parents was sufficient to attain high DES (requiring some lumen acidification), but inadequate to sustain the ApH necessary for NPQ generation. This perhaps indicates that the role of zeaxanthin as a quencher of reactive oxygen may be more important than its role in excitation dissipation (Niyogi, 1999 Baroli et al., 2003). Confirming earlier interpretations, we found that the mutants survived with high growth rates at VHL in spite of low PS II efficiency (ratio of variable to maximum fluorescence in dark equilibrated samples Fv Fm 0.28 - 0.36) and slow PS II electron transfer, either because of engagement of photoprotection, and or in spite of photoinactivation. The basis of the VHLR phenotype is evidently a...

Daily Essential Process

Toxic exposure is a fact of modern life and a health risk that is faced on a daily basis by patients regardless of how carefully they attempt to limit environmental sources of exposure. It is important to also look within the body to understand how to control the toxic load that arises from the body's inability to process and eliminate toxic substances. This is also relevant to the body's creation of toxins resulting from metabolic processes. This chapter reviews some common toxic substances and provides an overview of detoxification processes and how they can be supported clinically to maximize the body's healthy functioning and confer optimal protection.

Generation of O Ho Oh and other ROS in Plant Cells

Other important sources of ROS in plants that have received little attention are detoxification reactions catalyzed by cytochrome P450 in cytoplasm and ER. ROS are also generated in plants at plasma membrane level or extracellularly in apoplast. Plasma membrane NADPH-dependent oxidase (NADPH oxidase) has recently received a lot of attention as a source of ROS for oxidative burst, which is typical of incompatible plant-pathogen interaction. In phagocytes, plasma membrane localized NADPH oxidase was identified as a major contributor to their bacteriocidal capacity (Segal and Abo 1993). In addition to NADPH oxidase, pH-dependent cell wall peroxidases, germin-like oxalate oxidases and amine oxidases have been proposed as a source of H2O2 in apoplast of plant cell. pH-dependent cell wall peroxidases are activated by alkaline pH and in presence of a reductant produces H2O2. Alkalization of apoplast upon elicitor recognition precedes the oxidative burst and the production of H2O2 by...

Dietary Breakdown Products

Toxic breakdown products of protein metabolism include urea and ammonia. The old saying input equals output'' can be mirrored with the saying that output equals input.'' The breakdown processes that fuel the body by breaking down food yield toxic metabolic byproducts. Thus, it is important for patients to maintain a balanced diet and avoid excess that can strain biochemical pathways and provide extra demands on already challenged detoxification processes. Many labs are now providing testing to evaluate functional capacity of detoxification pathways as well as organic acids for cellular energy production.

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.

Negative Regulatory Components

Therefore it was proposed that the LSD1 protein functions as a transcriptional activator (Dietrich et al., 1997). Since LSD1 was recently shown to be part of a signaling pathway leading to the induction of copper zinc superoxide dismutase, it has been suggested that the spreading lesion phenotype of lsdl results from an insufficient detoxification of accumulating superoxide and other ROI, which then trigger a cell death cascade even in unaffected tissue (Kliebenstein et al., 1999).

Assimilation Of Sulphates Into Glutathione

Effecting positive control over sulphate uptake. Plants also have a very active pathway for the reductive assimilation of free inorganic sulphite into cys-teine in chloroplasts involving sulphite reductase (Ng and Anderson 1979). This pathway, which does not act on sulphate, is thought to be involved in the detoxification of S02 acquired from polluted air (Anderson 1990, De Kok 1990).

Cadmium and Copper Uptake and Homeostasis

Due to their redox-active properties, free Cu-ions in the cell are very toxic. Therefore, Cu is bound to chaperones that deliver it directly to the particular protein where its redox-active properties will be used in cellular functioning. For example, CCS chaperones deliver Cu to CuZnSOD in the chloroplast, COX chaperones deliver Cu to cytochrome c oxidase in mitochondria, and even for recycling of Cu from senescing tissues, CCH is used as a Cu chaperone (Palmer and Guerinot 2009 Robinson and Winge 2010). Besides these chaperones that are essential in normal functioning, detoxification of metals is achieved by specific chelators, which form non-toxic complexes with metals and facilitate their sequestration away from sensitive sites in cells. In this way, chelation prevents interaction of free metal ions with physiologically important proteins. The favoured ligands of the bivalent cations Cd2+ and Cu2+ are thiols (SH-groups), which are present on cysteine residues of glutathione (GSH),...

Basal Constitutive Response

In C. elegans, the DAF-2 DAF-16, the insulin-like signaling pathway regulates dauer formation, longevity, and the responses to environmental stressors and pathogens. It consists of the transmembrane tyrosine kinase insulin-like receptor DAF-2 and its downstream transducer DAF-16. The activation of this signaling cascade leads to the cytoplasmic retention of DAF-16, whereas its downregulation induces translocation of DAF-16 to the nucleus. In such circumstances, nuclear DAF-16 can activate the transcription of two classes of proteins (1) stress resistance proteins, which include those involved in detoxification (e.g. metallothioneins), oxidative stress (superoxidase dismutase, glutathione-S-transferase, catalase) and heat shock responses (2) the antimicrobial immune effectors (lysozymes, LYS-7, LYS-8, saposins, SSP-1, SSP-9, SSP-12, and thaumatins among others) (Lee et al. 2003 Murphy et al. 2003). DAF-16 can act as a transcriptional repressor or activator of gene expression (Shivers...

N functions and demand

The photosynthetic capacity of leaves is related to their N content mostly because the proteins of the Calvin cycle and thylakoids represent the greatest fraction of the leaf N content. Amounts of chlorophyll and the major enzyme of photosynthesis (RuBP carboxylase) are proportional to the leaf N content (Evans 1989). Because N is a component of amino acids and protein it is both structurally and metabolically important (Marschner 1995). In addition N can act as a signalling agent, e.g. for stomatal opening (Raven 2003). Signals derived from NO3- are involved in triggering widespread changes in gene expression that affect the intimate programming of C and N metabolism. Internal and external NO3- concentrations signal adjustments in root growth and architecture to the physiological state of the plant in relation to external N sources (Zhang et al. 1999, chapter 1) Excess or insufficiency will compromise any or all of the functions (see above). N demand, which tends to reflect the...

Effectiveness of Plant Defenses

While the physiological action of some plant chemical defenses is well established, and it is relatively easy to find plant chemicals that repel or poison animals or microbes, it is more difficult to demonstrate that chemical defenses benefit plants in nature, for three reasons. First, there has been repeated evolution of microbes and herbivores that can tolerate or detoxify plant defenses. Many of these plant pests can attack only the few plant species or even tissues to which they are adapted, but no plant

H2O2 Scavenging Catalases and Ascorbate Peroxidases

Hydrogen peroxide scavenging can be accomplished by both catalases (CAT) and ascorbate peroxidases (APX). In the regulation of H2O2 contents, CATs have a high reaction rate, but lower affinity to H2O2 as compared to APX. So CATs are more involved in H2O2 detoxification rather than the regulation of H2O2 as a signalling molecule. Catalases are heme-containing enzymes catalysing the reduction of H2O2 to H2O without any cellular reducing equivalents. A delicate balance between the CAT isoforms at transcriptional level, downregulation of CAT2 and upregulation of CAT1 3 was noticed in Arabidopsis plants exposed to Cd and Cu (Cuypers et al. 2011b). This correlates with the regulatory effects of senescence on CAT activities, indicating that CAT2 downregulation appears as the initial step in producing an elevated H2O2 level, which then leads to the induction of CAT3 expression and activity (Zimmermann et al. 2006).

Development Of Transgenic Plants Exploitation Of Hr For Disease Control

Other transgenes inducing lesion-mimic phenotypes encode components of downstream signaling pathways involved in HR development or compounds that activate or interfere with their function. Thus compounds that mimic ion fluxes across the plasma membrane, such as the bacterio-opsin, a bacterial proton pump, or cholera toxin, an inhibitor of GTPase and G-protein signaling, both induce HR-like cell death, which is correlated with PR gene expression and elevated disease resistance (Mittler and Rizhsky, 2000). Likewise, expression of metabolic enzymes that either generate peroxides (e.g., glucose oxidase) or antisense suppression of those that catalyze their detoxification (e.g., catalase, ascorbate peroxidase) was also found to induce

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...

Protein Based Biosensors

Again, a mutation rendering inability to synthesize SmtA protein leads to the metal-sensitive phenotype. The purified recombinant SmtA-fusion protein, overexpressed in E. coli as a carboxy-terminal extension of glutathione S-transferase, was immobilized in different ways to a self-assembled thiol layer on a gold electrode placed as the working electrode in a potentiometric arrangement in a flow analysis system. This allowed detection of copper, cadmium, mercury, and zinc ions at femtomolar concentrations 341 . Similarly, the regulatory protein MerR encoded by the mer operon of Tn50I in Pseudomonas aeruginosa, which controls the expression of itself as well as other mer gene products for mercury detoxification (by changing its conformation on binding to Hg2+ to align contacts at the promoter region of the operon-activating transcription of the mer genes) was also used as the recognition component of a biosensor. In both of these protein-based biosensors, GST-SmtA and MerR, a capacitive...

Wholecellbased Biosensors For Detection Of Bioavailable Heavy Metals

These systems can be used as the contaminant-sensing component of the biosensor by detecting the substance for which it is designed to detoxify or excrete. The contaminant-sensing component is combined with the reporter genes to create biosensors that can identify toxic substances at very low levels. When the contaminant-sensing component detects the substance, it triggers the reporter gene. In the development of a mercury-specific biosensor, a hypersensitive clone was constructed using the regulatory sequence along with the mercury (Hg+2) uptake genes merTPC of the mercury resistance operon. Such a clone was found responsive to Hg+2 with as low as 0.5 nM several folds lower than the lowest concentration required to induce the operon without the merTPC.

Conclusion and Future Perspective

Almost all biotic stresses lead to the overproduction of ROS in plants which are highly reactive and toxic and ultimately results in oxidative stress. Oxidative stress is a condition in which ROS or free radicals are generated extra- or intra-cellularly, which can exert their toxic effects to the cells. These species may affect cell membrane properties and cause oxidative damage to nucleic acids, lipids, and proteins that may make them non-functional. However, the cells possess well-equipped antioxidant defence mechanisms to detoxify the detrimental effects of ROS. The anti-oxidant defences could be either non-enzymatic (e.g. glutathione, proline, a-tocopherols, carote-noids, and flavonoids) or enzymatic (e.g. SOD, catalase GPX, and GR). It is well known that plant cells and its organelles like chloroplast, mitochondria, and peroxisomes employ antioxi-dant defence systems to protect themselves against ROS-induced oxidative stress.

Cd Uptake from Soil to Roots

Most studies have shown that the main site of Cd accumulation in roots is the apoplast, particularly cell walls. Using energy-dispersive X-ray microanalysis, Cd was determined in cortex parenchyma cells, endodermis, parenchyma cells of the central cylinder, and xylem vessels in T. caerulescens (Wojcik et al. 2005). After treatment with 20 ppm Cd, about 13 of the total Cd in T. caerulescens roots was associated with organic acids (Boominathan and Doran 2003). Nedelkoska and Doran (2000) have found retention of almost the whole pool of Cd taken up in the fraction of cell wall of Thlaspi roots, and then diffused into the symplast after 7-10 days of exposure to 200 p.M Cd. The authors also suggested that such a delay in Cd transport through membranes inside cells is an important defense mechanism against Cd toxicity, enabling simultaneous activation of intracellular detoxification mechanisms of Cd such as chelation and antioxidative defense.

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...

Interactions Between Iron and Sulfur Cycling

Recent studies have investigated the importance of iron pools in carbonate sediments as a buffer against sulfide toxicity. Iron additions to T. testudinum growing on carbonate sediments resulted in increased above-ground biomass and it was suggested that decrease of sulfide levels due to enhanced precipitation of iron-sulfides, and thus detoxification, improved plant performance (Chambers et al., 2001). Iron additions have also been made to organic-enriched carbonate sediments with the slow-growing seagrass P. oceanica (Holmer et al., in press). Here it was found that, in addition to the improved sediment conditions, the availability of iron also increased, and the activity of the iron-demanding alkaline phosphatase enzyme increased. The uptake of phosphate was stimulated and seagrass growth increased. This is consistent with previous findings of iron deficiency in seagrasses growing in carbonate sediments (Duarte et al., 1995).

Mechanisms In Amf To Tolerate Ptes

Levitt 57 proposed three basic strategies for organisms dealing with high PTE concentrations avoidance, detoxification, and biochemical tolerance. The avoidance mechanism involves PTE exclusion mechanisms, which operate at two levels restriction of uptake and restriction of transport. The process of detoxification is essentially similar, but avoidance of toxicity results from subcellular PTE concentration or by binding. Biochemical tolerance reflects the presence of specialized metabolic pathways and enzymatic adaptations.

Results And Discussion

Several members of the Poaceae were checked for BOA detoxification capacity the results are presented in Table 4.1. All species, with one exception, contained the W-glucoside, although there were remarkable differences in the accumulated amounts following incubation at 24 h and 48 h. Zea mays exhibited the most effective detoxification capacity, as BOA-6-O-glucoside was synthesized in traces only or was a minor product. The W-glucosylated compound already BOA detoxification of several Poaceae species containing benzoxazinones are bold printed. BOA detoxification of several Poaceae species containing benzoxazinones are bold printed. The synthesis of BOA-6-O-glucoside is catalyzed by constitutive enzymes that may be upregulated. A glucosyltransferase that accepted BOA-6-OH as a substrate was measurable in protein extracts of corn roots harvested from control plants. Detoxification via glucoside carbamate synthesis is inducible and seems to be more complicated than simple N-glucosylation...

Reactions on green pigments 2321 Chlorophyllase

A typical N-terminal transit peptide is missing in some of the cloned CLHs, such as Arabidopsis CLH1 or CaCLH1 from Chenopodium album. Instead, Ca-CLH1 seems to be glycosylated and has motifs suggesting localization in the vacuole (Tsuchiya et al., 1999). This absence was explained by a possible second pathway localized inside the vacuole, where CLH together with unknown oxidases would ca-tabolize chl (Takamiya et al., 2000). The finding of a mass exodus of chl-containing globules from senescent chloroplasts (Guiamet et al., 1999) supported this idea. But so far neither the oxidases nor catabolites of such a pathway have been found. Experiments on subcellular localization and the analysis of mutants will be required to elucidate the in vivo role of CLHs. Notably, downregulation of AtCLH1 did not cause an obvious senescence-related phenotype (Benedetti and Arruda, 2002 Kariola et al., 2005), and a role of AtCLH1 in regulating defense pathways in plants through the detoxification of...

Cell Wall Binding and Vacuole Sequestration

Plants have a range of potential mechanisms at the cellular level that might be involved in the detoxification and thus tolerance to heavy metal stress (Hall 2002). Cell wall binding and vacuolar sequestration are the two essential detoxification mechanisms that play a vital role in hyperaccumulation of heavy metals (Cosio et al. 2004). hydroponically, Zn and Cd were accumulated in the cell wall of the rhizosphere as Zn Cd phosphates (Kupper et al. 2000). Cell wall binding can prevent Cd from being transported across the plasma membrane. This delay in transmembrane uptake may represent an important factor in the defense against Cd poisoning in T. caerulescens, allowing time for activation of intracellular mechanisms for heavy metal detoxification (Nedelkoska and Doran 2000). The vacuole, in turn, is generally considered to be the main storage site for metals in yeast and plant cells (Salt and Rauser 1995). Compartmentalization of metals in the vacuole is also part of the tolerance...

Evolution of Cd Hyperaccumulation

Apart from the numerous studies on physiological and molecular mechanisms involved in Cd hyperaccumulation and detoxification, as discussed above, perhaps the most fundamental question is why these unusual species accumulate Cd to concentrations that are toxic to most other organisms. Since 1990s, the ecological and evolutionary significances of metal hyperaccumulation have attracted considerable attention. Five principal hypotheses have been postulated, including drought resistance, metal tolerance disposal, elemental allelopathy, inadvertent uptake, and defense against herbivores or pathogens (Boyd and Martens 1998). There is little evidence linking hyperaccumulation with drought resistance, metal tolerance disposal, and elemental allelopathy (Boyd 2004 Mcnair 2003). According to the inadvertent uptake hypothesis, Cd accumulation is possibly mediated by channels

Metallomics And Metallomes

Organic acids play a role in metal chelation by forming complexes with metals, a process of metal detoxification. Chelation of metals with exuded organic acids in the rhizosphere and rhizospheric processes indeed form an important aspect of investigation for remediation. These metabolic pathways underscore the physiological, biochemical, and molecular bases for heavy metal tolerance 6 .

Antioxidant Systems Under Cd Stress

(Leon et al. 2002) and sunflower (Laspina et al. 2005), while the opposite effect was observed in radish roots (Vitoria et al. 2001). Especially interesting is that light may interfere with the Cd-dependent catalase activity, as it has been shown that Cd2+ treatment of leaf discs under light decreased CAT activity and increased carbonyl groups content, which suggested that CAT inactivation could be due in part, to the oxidation of the protein under this condition (Azpilicueta et al. 2007), although in pea plants treated with Cd, no changes in the pattern of CAT oxidation were observed (Romero-Puertas et al. 2002). In addition to CAT, the enzymes of the ascorbate-glutathione cycle also remove H2O2, especially in cellular compartments where H2O2 exits and there is no catalase (Gutteridge and Halliwell 2000). This cycle is composed of four enzymes ascorbate peroxidase (APX), monodehy-droascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glu-tathione reductase (GR) which...

Overexpression Of Mts As A Means To Increase Cadmium Tolerance

An important pathway by which plants detoxify heavy metals is through sequestration with heavy metal-binding peptides called phytochelatins or their precursor, glutathione. To identify limiting factors for heavy metal accumulation and tolerance and to develop transgenic plants with an increased capacity to accumulate and or tolerate heavy metals, the Escherichia coli gshII gene encoding glutathione synthetase (GS) was overexpressed in the cytosol of Indian mustard (Brassica juncea). The transgenic GS plants accumulated significantly more Cd than the wild type shoot Cd concentrations were up to 25 higher and total Cd accumulation per shoot was up to threefold higher. Moreover, the GS plants showed enhanced tolerance to Cd at the seedling and mature plant stages. Cd accumulation and tolerance were correlated with the gshII expression level. Cd-treated GS plants had higher concentrations of glutathione, phytochelatin, thiol, S, and Ca than wild-type plants. The conclusion was that, in...

How to Deal with the Oxygen Dilemma of Nitrogen Fixation

Frankia does not form vesicles (Berg and McDowell 1987), but the plant provides an oxygen diffusion barrier via an unusually hydrophobic type of lignification of the walls of infected cells (Berg and McDowell 1988) that leads to a microaerobic environment in these cells, and discontinuity in the intercellular air spaces (Zeng et al. 1989). The similarity with the oxygen protection systems of legume nodules is further underlined by the fact that high amounts of a symbiotic hemoglobin are formed in the infected cells of Casuarina nodules (Fleming et al. 1987 Jacobsen-Lyon et al. 1995). While hemoglobins were also found in the infected cells of other actinorhizal nodules (Alnus sp. Suharjo and Tjepkema 1995 Sasakura et al. 2006 Myrica gale Pathirana and Tjepkema 1995 Heckmann et al. 2006 Datisca glomerata Pawlowski et al. 2007), these were class I hemoglobins (Alnus, Myrica) or truncated hemoglobins from plants (Datisca) which are not implicated in O2...

NO Function and Protection Under Cd Stress

Recently, a study in which CATMA arrays were used, has shown the effects of NO in roots of Cd2+ treated plants (Besson-Bard et al. 2009). Forty-three genes related to iron homeostasis, proteolysis, nitrogen assimilation metabolism and root growth, were identified to as being regulated by nitric oxide. NO can also regulate cellular responses through posttranscriptional modifications such as S-nitrosylation of proteins (Lindermayr et al. 2006 Romero-Puertas et al. 2008). A decrease in S-nitrosylation of CAT protein under Cd stress was observed (Romero-Puertas et al. submitted). CAT, a key enzyme involved in H2O2 detoxification in peroxisomes is S-nitrosylated during physiological conditions (Romero-Puertas et al. submitted) and the reduction in S-nitrosylation could be related to the slight increase in CAT activity previously observed in isolated pea leaf peroxisomes (Romero-Puertas et al. 1999). Additionally, it has been shown that in plants treated with Cd there is an increase in the...

Regulatory Aspects Of The Glutathione System Under Stress Impact

The control of glutathione pool and the glutathione redox state itself seems to be even more complicated (Figure 5). Glutathione synthesis is apparently under redox control, possibly by GSH GSSG ratio itself. In Arabi-dopsis, the translation of protein for y-GC synthetase, the rate limiting enzyme for GSH synthesis, is repressed by high GSH GSSG ratios. (Xiang and Betrand 2000). Furthermore, sulphur assimilation into cysteine as a requirement for GSH synthesis can also be oxidatively induced. For example, the expression rates and the activities of the key enzymes APS-reductase and ATP-sulphurylase (but not cysteine-synthetase) increased upon a decreased GSH GSSG-ratio in maize roots. This is even more remarkable because most enzymes of assimilation pathways in the chloroplasts are induced under the reducing conditions of a highly active light-driven electron transport (Fluck-inger et al. 2000). ATP-sulphurylase activity increased in canola roots upon mild oxidative stress, which also...

Organelles Involvement in Cd Stress

ROS production after cadmium stress differs in the nature of the source and localization in the cell. It seems that NADPH oxidase from plasma membrane is one of the first enzymes involved in ROS production in response to heavy metal (Olmos et al. 2003 Garnier et al. 2006). Other organelles, however, such as mitochondria (Garnier et al. 2006), peroxisomes (Romero-Puertas et al. 1999) and chloroplasts (Bi et al. 2009), are also involved and play a key role in ROS release and or detoxification in response to Cd. Several studies have shown that the vacuole is a site of accumulation of different heavy metals (Cobbett 2000 Verbruggen et al. 2009). Actually, chelating complexes formed by Cd can be transported into the vacuoles, preventing the free circulation of Cd ions and placing them into a limited area (Sanita di Toppi and Gabrielle 1999). On the other hand, it has been reported that Cd2+ increase H2O2 and O2 - accumulation in mitochondria (Heyno et al. 2008 Garnier et al. 2006)....

Physiological pathways involving Cblcipk signaling modules

An increase in Ca2+ levels in the cytoplasm (Pauly et al, 2000), salt tolerance could therefore involve Ca2+ signaling and the signal could be transmitted via CBL-CIPK pathways for salt detoxification (Hasegawa et al., 2000). In this context, studies have established that SOS3 CBL4-SOS2 CIPK24 may directly regulate the downstream component SOS1, a putative Na+ H+ antiporter (Shi et al., 2000), thereby enhancing the salt detoxification process. More recent studies (Kim et al., 2007 Quan et al., 2007) placed another CBL, CBL10, in the salt tolerance pathway. Interestingly, CBL10, like SOS3 CBL4, also interacts with and appears to function through SOS2 CIPK24. However, unlike SOS3 CBL4 that functions mainly in the roots, CBL10 is expressed and functions almost exclusively in the shoots leaves (Kim et al, 2007 Quan et al, 2007). Perhaps the most unique feature of the cbl10 mutant is that the mutant plants, despite being more sensitive to salt, accumulate less salt than the wild type (Kim...

Significance of chlorophyll breakdown

Modifications and subsequent disposal of FCCs in the vacuole are reminiscent of the stepwise detoxification in plants of herbicides and xenobiotics. After hydroxyla-tion and conjugation with different moieties to increase their water solubility, these compounds are detoxified by export from the metabolically active cytoplasm. From this point of view, chl degradation in higher plants can be regarded as chl detoxification required to safely dispose this potential phototoxin during senescence (see below). In contrast, C. protothecoides does not need such a mechanism and the first water-soluble product of porphyrin macrocycle cleavage, RCC, is excreted into the surrounding medium. Consequently, 'invention' of RCCR for the intracellular metabolism of RCC can be regarded a prerequisite for land colonization of plants during evolution.

Proteomics of Plant Hyperaccumulators

Abstract Plant metal hyperaccumulators take up and detoxify high concentrations of metal ions in their roots and shoots. They constitute an exceptional biological material for understanding mechanisms regulating plant metal homeostasis and plant adaptation to extreme environments. Hyperaccumulation physiology has recently also been studied with molecular tools. Indeed making use of transcriptome analysis it has been demonstrated that different expression patterns of genes accompanied different responses to metals between hyperaccumulator and non-hyperaccumulator plant species. The proteomic approach can also be powerful in dissecting the hyperaccumulator phenotype and the complex involvement of the protein regulation in this phenomenon. This chapter focuses on the recent developments in the application of proteomics to the analysis of hyperaccumulators providing a comprehensive review of key literature data of plant metal in particular Cd, Ni and Zn hyperaccumulation.

Chl breakdown and cell death

The reactions ofPAO and RCCR cause the loss of green pigment color and, therefore, are most important for the detoxification of chl during senescence. The importance of chl breakdown is corroborated by the analysis of respective mutants. Thus, mutations in, or antisense expression of, Pao and Rccr induce light-dependent cell death phenotypes (Greenberg and Ausubel, 1993 Greenberg et al., 1994 Gray et al., 1997, 2002 Mach et al., 2001 Spassieva and Hille, 2002 Pruzinska et al., 2003, 2005 Tanaka et al., 2003), and accumulation of pheide a was demonstrated to be responsible for cell death induction in the case of PAO mutants (Pruzinska et al., 2003, 2005 Tanaka et al., 2003). In acd2-2, RCC accumulates during senescence, and contents of RCC have been shown to correlate with the progression of cell death (A. Pruzinska and S. Hortensteiner, unpublished). In addition, treatment of leaves or of isolated protoplasts with proto IX induced cell death in the mutant (Yao et al., 2004). Thus it...

Cellular Regulation and Targeting 431 Nuclear Localized Parasitism Proteins

The hypodermis is a syncytial cell layer directly beneath the (nonliving) nematode cuticle that forms the new cuticle during molts and secretes a number of molecules for deposition on the cuticle surface of the nematode body (Bird and Bird 1991) . Several genes expressed within the hypodermis encode proteins deposited on the cuticle surface that are in direct contact with host cells during nematode invasion of plant tissues. Among the dynamic mixture of proteins at the cuticle surface are proteins with potential roles in mitigating host defense response. Peroxidase genes are expressed in the potato cyst nematode hypodermis (Jones et al. 2004 Robertson et al. 2000), and the peroxidase proteins accumulate on the nematode body surface presumably to detoxify reactive oxygen species generated by the defense response of the host (Waetzig et al. 1999). An antiserum that bound to surface molecules of potato cyst nematode isolated cDNA expressing a homologue to the fatty acid- and...

The Dynamic Mitochondrial Proteome Tissue Type Differences and Response to Development and Stress

Differential analysis of the mitochondrial proteome was applied to the study of Ara-bidopsis mitochondria subjected to different oxidative stresses, as well as pea plants subjected to drought, cold stress, and herbicide treatments to mimic environmental challenges 29, 30 . Changes in detoxification mechanisms (as determined by proteins with increased abundance), together with proteins prone to oxidative damage (as judged by decreased abundance or the presence of breakdown products), provided insights into the dynamics of plant mitochondria in response to oxidative stress. The targets of oxidative modification in plant mitochondria have also been studied by identification of proteins that have undergone carbonylation 31 . A recurring outcome of these studies indicates the presence of a subset of proteins with enhanced susceptibility to oxidative damage, exemplifying the potential of proteomics toward elucidating the metabolic consequences of stress in plant mitochondria.

Gene Expression Responses of Plants to High Light Stress

In contrast, many other genes were up-regulated by high light. In Synechocystis, expression of genes homologous to heat shock genes in other organisms were significantly induced by high light (Hihara et al., 2001). Genes encoding scavenging enzymes for ROS, such as glutathione peroxidase, and two FtsH homologs were also up-regulated by high light. In Arabidopsis, genes involved in ROS detoxification such as ascorbate peroxidase 1 and glutathione- -transferase 6 were up-regulated (Rossel et al., 2002 Kimura et al., 2003). In addition, chalcone synthase gene in the anthocyanin pathway and the -carotene hydroxylase II gene in xanthophyll biosynthesis were up-regulated (Rossel et al., 2002). The accumulation of anthocyanin and lignin by high light stress was determined (Kimura et al., 2003). Interestingly, gene expression of many heat shock proteins (HSPs) such as HSP70-3, HSP90, and HSP81-2 was increased by high light (Rossel et al., 2002 Kimura et al., 2003) and even by the filtered...

Multidrug Resistance Transporter MRP

The involvement of a multidrug resistance-type transporter in sequestering anthocyanins in the vacuole was suggested by three observations (i) vana-date, a specific inhibitor of ABC transporters, blocks vacuolar accumulation of anthocyanins (Marrs et al. 1995) (ii) the requirement of GST for vacuolar localization of anthocyanins is reminiscent of GST-mediated detoxification pathways for heterocyclic organic xenobiotic molecules (Marrs et al. 1995) and (iii) two genes for MRPs were upregulated in cells engineered to overexpress anthocyanin regulators (Bruce et al. 2000). ESTs corresponding to

Oxidative Stress and Cell Defenses

Ascorbate peroxidase is found in higher-order plants, chlorophytes, and red algae. This enzyme has a high specificity for ascorbate (or ascorbic acid) as the reducing substrate, and it subsequently catalyzes the reduction of hydrogen peroxide into water (Carvezan 2008). The ascorbic acid acts both as a cofactor and reducing agent for the enzyme, allowing the enzyme to detoxify various organic radicals, counteract O2' and H2O2 and remove active oxygen (Halliwell and Gutteridge 1989).

Some plants emit prussic acid when wounded by animals

If the cell is wounded by feeding animals, the compartmentation is disrupted and the glycosidase comes into contact with the cyanogenic glycoside. After the hydrolysis of the glucose residue, the remaining cyanhydrin is very unstable and decomposes spontaneously to prussic acid and an aldehyde. A hydroxynitrile lyase enzyme accelerates this reaction. The aldehydes synthesized from cyanogenic glycosides are often very toxic. For a feeding animal, the detoxification of these aldehydes can be even more difficult than that of prussic acid. Due to the formation of the two different toxic compounds, cyanogenic glycosides are a very effective defense system.

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

Stress Response Circuits in Context

Generally, drought can be integrated into a global stress recognition and integration response network that can provide a view of underlying complexities (Fig. 13.1). Sensing of a particular stress condition includes specific reactions that identify the stress, but owing to the sensing of injury that accompanies any stress, different responses are elicited by additional signalling pathway or pathways that measure injury. While the abiotic stress-specific pathways lead to responses that are to some degree known, signal integration begins to affect cell division expansion, growth, and development. Initiated by injury, for example, the components of endoplas-matic reticulum and denatured protein signals, detoxification signals begin to control damage and affect repair reactions. Depending on the severity of a stress, repair and stress-specific countermeasures can lead to tolerance, but may also lead to (programmed) cell and plant death (Fig. 13.1). Many components linking tolerance to...

Natural Functions Of

Natural functions for the GST have been discussed since their discovery. The ubiquitous distribution and the abundant presence of GST in various tissues of animals and plants may be a sign for their obvious importance. GST of mammals, especially rodents and human have been investigated thoroughly for their physico-chemical and catalytic properties (Mannervik und Danielson 1988, Picket and Lu 1989, Daniel 1993) because of their important role in toxin conjugation, drug metabolism and anticancer therapy. Natural functions of GST in plants have only scarcely been investigated (Table 5). However, there are several reports on the detoxification of toxic endogenous metabolites. For example, in wheat all eight characterized iso-forms have activity with crotonaldehyde and an isothiocyanate. Furthermore, they exhibit all glutathione peroxidase activity as do certain maize GSTs. Phytohormones, fungal and bacterial toxins may also be conjugated, but experimental evidence is scarce....

Other Members Of The Mate Family

Functionally characterized members of the MATE family appear to efflux low molecular weight organic compounds from the cell cytoplasm either out of the cell or into a subcellular compartment (for a summary, see Rogers and Guerinot, 2002). There are at least 56 MATE family members in Arabidopsis (Li et al., 2002 Rogers and Guerinot, 2002). They play roles in processes as diverse as salicylic acid localization, flavonoid transport, and detoxification. Therefore it is very difficult to predict a function for a newly discovered MATE protein simply based on protein sequence similarity to a previously characterized MATE family member.

Involvement of Plant Antioxidant Systems in ROS Signaling

The balance between ROS production and ROS scavenging is a critical aspect for redox homeostasis. This balance can be altered by abiotic and biotic stress conditions. During normal cell metabolism ROS content has to be maintained at a low steady-state level however, as it has been already mentioned, new ROS are continuously produced in aerobic organisms. The continuous presence of ROS, whose concentration depends on the environmental conditions or on cell tissue developmental phase, might have moved the evolution to use ROS as molecular signals in several processes. In particular, plant growth and development as well as hormonal signaling and the activation of defense mechanisms also depend on the alteration in ROS levels. It has been observed that treatments with CAT of soybean cells inoculated with avirulent pathogens block the induction of plant defense genes, such as those encoding for glutathione peroxidase and glutathione transferase (Levine et al. 1994). The latter enzyme is...

Anticarcinogenic activity

Banerjee et al. (1994) has found that cardamom oil enhances glutathione-S-transferase enzyme and acid soluble sufhydril activities. These enzymes mediate the oxidation and detoxification of xenobiotics. Cardamom oil was fed by gavage at 10 fxl day for 14 days and hepatic microsomal enzymes were measured. GST and acid-soluble sulfhydril were found to be significantly elevated (P 0.1, P 0.001 and P 0.05 respectively).

Compartimentation Of Glutathione Conjugates

On the background of these metabolism data, it is logical that glutathione conjugates may be intermediates rather than end products of detoxification. This topic has been reviewed extensively elsewhere (Schr der 1997). Elaborate investigations of herbicide metabolism in several plant cell cultures have elucidated that GS-conjugates have only short lifetimes in the cultured cells, and that they are rapidly further metabolized. First evidence for the enzymatic background of these cleaving reactions has been obtained only recently. Wolf et al. (1996) identified a specific carboxypeptidase for the cleavage of xenobiotic glutathione conjugates in the vacuoles of barley. Car-boxypeptidases are exopeptidases cleaving terminal amino acids from poly-peptides, whereas the physiological role of endopeptidases would be the regulation of enzyme activities via the cleavage of internal peptide bonds in polypeptides (Zuber and Matile 1968). A natural function for exopeptidases has been found in the...

Nonspecific Metal Chelating Agents Low Molecular Weight Organic Acids

LMW organic acids perform important and varied metabolic roles for living cells and also participate in the mobilization and uptake of a series of mineral nutrients (e.g., Fe and P), essential to the metabolism of plants and most microorganisms in the soil. LMW organic acids are directly involved in the biogeochem-ical cycles of a variety of metal elements they serve as pathogenic agents for certain fungi and as wood biodeterioration agents for others and they have been involved in the detoxification of metal ions in plants, fungi, and bacteria (Dutton and Evans 1996 Jones 1998 Gadd 1999, 2007 Landeweert et al. 2001). Although LMW organic acids are important agents for the mobilization of mineral nutrients from inorganic sources, the strategy most utilized by ECM fungi for the mobilization of N and P from organic sources is enzyme production. Both strategies are used with more or less efficiency depending on the fungal species (Chalot and Brun 1998 Landeweert et al. 2001). citrate...

Biotechnological Potential of ECM Fungi Producing Metal Chelating Agents

The revegetation of metal-contaminated soils is another important application of plants mycorrhized with ECM fungi producing a wide range of chelators siderophores, LMW organic acids, MTs, PC, and GSH. Given that these chelators contribute to the detoxification of metals through intracellular or extracellular mechanisms, the fungal species that produce them must protect their host plants in contaminated environments. This protection consists of excluding metals or accumulating them in their fruiting bodies, using both ways to prevent their entry into the mycorrhized roots. The use of plants in the bioremediation of soils contaminated by metals, aided by synthetic chelators like EDTA and called assisted

Acute Dermal Toxicity

The acute dermal toxicity test ascertains whether a specific LD50 dose will cause problems if applied dermally. Some chemicals may be as toxic dermally as orally. But tea tree oil, as with most essential oils, is not as toxic dermally as it is orally. This is most likely due to the slow absorption of the oil into the body through the skin, thus allowing organs, such as the liver, time to detoxify it and the kidney to eliminate the metabolites of the toxic material.

Mechanisms of herbicide resistance 1221 Target site resistance

There have been only limited reports of resistance to this class of herbicide and little is known regarding the resistance mechanisms responsible. No evidence of target-site resistance involvement has yet been found and it is thought that most cases of resistance are a result of enhanced herbicide metabolism or sequestration away from the site of action. In Lolium perenne and Conyza bonariensis increased levels and activities of enzymes that detoxify active oxygen species have been measured in resistant biotypes. These are superoxide dismutase, ascorbate reductase and glutathione reductase (Shaaltiel and Gressel, 1986). Other studies with C. bonariensis have suggested the immobilisation of paraquat in resistant biotypes, possibly by binding to cell wall components, so that less of the herbicide can reach the thylakoid. Alternatively, paraquat uptake and movement may be reduced in resistant biotypes of Hordeum glaucum.

Oxidative Air Pollution Ozone And Others Occurrence and phytotoxicity

And 0.7 p.mol ascorbate g 1 needle dry weight in the apoplastic space. In other studies, GSH was unmeasurably low in the apoplastic space, such as in beech trees (Luwe 1996) or herbaceous plants (Lyons et al. 1999, in Plan-tago major). These findings confirm that in contrast to ascorbate, glutathione is not an important factor in the 'first line of defence', the antioxidant system of the cell walls (Polle 1998). However, since ascorbate is mainly regenerated through the action of the enzymatic ascorbate-glutathione cycle (Figure 3), cytoplastic GSH is indirectly involved in the apoplastic detoxification capacity of ascorbate. Since the presence of the enzymes of the ascorbate-glutathione-cycle in the apoplast is questionable, the dehydroascorbate formed by oxidation of ascorbate must be transported into the cytoplasm and regenerated therein (Figure 3). A corresponding ascorbate dehydroascorbate translocation system in the plasmalemma exists (Horemans et al. 1998). This process...

Overall Naturopathic Approach

There is some evidence that, for many patients, a week of fasting followed by a vegetarian diet will reduce the symptoms of RA over the course of a year.38 During the fasting period of the study cited, subjects were allowed to eat garlic, vegetable broth, a decoction of potatoes and parsley, herbal teas, and the juices of carrots, beets, and celery. (Note that, in addition to potentially suppressing the immune system because of hypocaloric intake, this fasting diet also provides an excellent source of phytochemicals that assist in detoxification and is itself rich in antioxidants.) Following the fasting, subjects introduced new foods one at a time, discontinuing them if any increase in pain, stiffness, orjoint swelling was noticed. If, after a week of waiting, reintroduction resulted in a repeat exacerbation, then that item was removed for the rest of the study period. New food items being introduced excluded gluten, meat, fish, eggs, dairy foods, refined sugar, citrus, salt, strong...

ROSinduced Cell Death Network

In addition to calcium-dependent protein kinases, a vast network of mitogen-activated protein kinases (MAPK) is involved in relaying the ROS signal. PCD triggered by chloroplast-derived H2O2 is orchestrated by a MAPK kinase cascade (Liu et al. 2007). The MAPK kinase kinase MEKK1 is regulated by different stresses and H2O2 in a proteasome-dependent manner (Nakagami et al. 2005). Compromising MEKK1 results in impaired H2O2-induction of the downstream kinase MPK4. Surprisingly, MEKK1 can interact directly with WRKY53, a transcription factor involved in senescence-induced PCD, thus bypassing downstream kinases (Miao et al. 2007). Another H2O2-inducible MAPK kinase kinase, Arabidopsis ANP1, activates two downstream MAPKs, AtMPK3 and AtMPK6, to eventually regulate gene expression of specific H2O2-inducible transcripts (Kovtun et al. 2000). Interestingly, AtMPK3 and AtMPK6 are induced also by the serine threonine kinase OXI1, which in turn can be activated by H2O2 and abiotic stress (Rentel...

Application to bioindication

Two main classes of biomonitoring techniques, direct and indirect, can be distinguished. Direct biomonitoring techniques use organisms as in situ biological assays of pollution levels. This is how bryophytes are most often used in biomonitoring, with pollutant concentrations being directly measured in moss tissues. Sometimes, indicators of plant stress, such as pigment ratios (Lopez et al. 1997) or the concentration of enzymes involved in the detoxification process of pollutants (Roy et al. 1995, Schrenk et al. 1998), are also used. Indirect biomonitoring, by contrast, involves detecting how variation in community attributes, such as species composition, abundance and diversity, may be explained by changes in the environment.

ZnCdCoPb P1bATPases in Plants Physiological Roles and Biological Interest

Abstract P1B-ATPases are cation transporters found in all organisms. In plants, they are found in almost all membranes including plasma membrane, internal chloroplastic membrane, thylakoids, post-Golgi and tonoplast, where they manage nutrient fluxes (Cu+, Zn2+) as well as detoxification of toxic cations (Co2+, Cd2+, Pb2+, high Zn2+). All P1B-ATPases from Arabidopsis thaliana have now been characterized they are involved in plant-scale and cell-scale cations fluxes. Orthologs of these genes are being characterized in other species such as rice or soybean, and their expression domain and roles are similar to those of Arabidopsis. Orthologs from hyperaccumulator species, such as Arabidopsis halleri or Thlaspi cearulescens, have been found to be over-expressed due to the presence of strong promoters and gene duplications. They have recently been shown as essential in the hyperaccumulators properties. Our knowledge about plant P1B-ATPases opens new fields of investigation in biotechnology...

Water Regime And Photosynthesis Under Salt Stress

Ological traits associated with maintaining water relations and photosynthesis (e.g. different pathways of carboxylation, such as C4, intermediate C3-CAM and CAM) (Dajic et al., 1997a). Additionally, various metabolic changes, such as the maintenance of ion and molecular homeostasis (e.g. synthesis of compatible solutes necessary for osmotic adjustment), detoxification of harmful elements and growth recovery, which depends mainly on various signaling molecules, occur under exposure to salt drought stress (Xiong and Zhu, 2002).

Coffee And Gastrointestinal And Liver Health

Because of the unique relationship between caffeine and the hepatic microsomes that metabolize it, it has been proposed that fasting plasma caffeine concentration may serve as a guide to measuring the physiologic impairment arising from chronic liver disease.59 Caffeine can provide, via hepatic detoxification testing, information on whether an imbalance between phase 1 and phase 2 detoxification pathways are present. The unique physiologic impact of caffeine in the liver has also led to research on the relationship between serum gamma glu-tamyltransferase a measure of liver damage and smoking that suggests coffee may help mitigate some of the damage associated with smoking demonstrated by decreased induction of gamma glutamyltransferase in smokers.60 What also supports this trend is an observation of an increase in gamma glutamyltransferase in women from Norway who decreased their consumption of boiled coffee.

Genes involved in the storage of iron

Nicotianamine may also play a role in Fe detoxification, as its Fe complexes are thought to be relatively poor Fenton reagents (von Wiren et al., 1999). Immunocytochemical observations of NA showed that Fe-loaded pea plants had increased NA concentrations in the vacuole, possibly sequestering and detoxifying excess Fe (Pich et al., 2001).

Interest in Phytoremediation

AtHMA4 and its orthologs are interesting since they allow a higher translocation of Zn2+ and Cd2+ and presumably Pb2+ and Co2+ from the roots to the shoot (Verret et al. 2004), allowing a detoxification of the roots and thus a better tolerance of the plant and a higher yield of phytoextraction. While the increase in Zn2+ and Cd2+ transfer in 35S AtHMA4 transgenic plants was less than a doubling, the first experiments on actual polluted soils have shown that the transgenic lines were able to extract 3.1-fold more Cd2+ and 2.8-fold more Zn2+ than the wild-type plants (C. Sarrobert, Institut de Biologie Environnementale et Biotechnologies, France, personal communication). Thus, a major interest of HMA4 is to give a selective advantage in case of a multi metallic pollution and this may be the reason why this gene has been under a high selection pressure in hyperaccumulators which have to face such types of environment. Genes encoding AtHMA4 orthologs have been found highly expressed in...

Cyanogenic Glycosides

Most microorganisms are not sensitive against cyanide because of their ability to use the cyanide insensitive alternative respiratory pathway and their capability to detoxify cyanide, respectively (Selmar 1999). Further information about biochemical, physiological and nutritional aspects of cyanogenic glycosides is given by Selmar (1999).

Subcellular Proteome in Defense and Stress Responses

Chloroplasts and Mitochondria Subcellular fractionation and purification of organelles have provided attractive advantages to low-abundance protein separation in proteomic analysis. The proteomes of some organelles such as chloroplast, mitochondria, nuclei, and other subcellular compartments were studied in plants. Of the organelles, the chloroplast and the mitochondria proteomes are by far the most comprehensively studied. However, these organelles were not investigated in the plant defense proteome. The resistance response against pathogen attack usually triggers a rapid HR that is tightly associated with rapid changes in calcium influx, generation of ROS, expression of PR proteins, production of phytoalexins, and cross-linking of components of the cell wall. Both chloroplasts and mitochondria are additional potential sources of ROS and possess well-developed mechanisms to rapidly detoxify free radicals. Therefore, changes to the proteome of chloroplasts and mitochondria are of...

And Chemical CaMg Ratio LMWOAs Factors Influencing Phytoremediation Efficiency

In the broad spectrum of organic compounds present in the rhizosphere, particular attention is focused now on LMWOAs. Organic acids such as malic, oxalic, acetic or citric are recognized as the most significant ones in many different processes in the rhizosphere. Depending on their degree of dissociation (efficiency), and the amount of carboxylic groups in the molecule, acids can appear in the form of differently charged anions, which in consequence results in the possibility of metal cations' complexation and relocation from the soil. This is the reason that acids are reported as components of the soil environment which in the rhizosphere take part in many processes, e.g. in dissolving and uptake of nutrients (e.g. P and Fe) by plants and microorganisms, decrease of stress associated with anaerobic conditions, dissolving soil minerals leading to pedogenesis, and detoxification of heavy metals by plants (e.g. Al).

Common Changes in the Proteome in Response to Different Abiotic Stresses

Although we have summarized the recent proteome studies on stress responses for single stress factors, it is evident that under many natural conditions the plants have to respond to a combination of stresses. Consistent with biochemical and molecular data, proteome approaches also indicate an overlap in the cellular responses to different stresses, such as detoxification of ROS by enzyme components as a ubiquitous element of defense. It should also be mentioned that due to limitations in current techniques, proteome analysis is likely to be restricted to the more abundant proteins of central metabolic pathways, implying that specific aspects of cellular responses characteristic to certain stress factors might not yet be detected with current methodology. However, a survey of published data indicates that in many experimental systems, fundamental reprogramming of central metabolic routes can be monitored. Whereas changes in the abundance of proteins representing house-keeping functions...

A 20052006 Update Of The Contribution Of Proteomics To Rnf Symbiosis

Transformation of a free-living bacterium to a nitrogen-fixing bacteroid results in significant physiological and developmental changes in rhizobia. To understand the cellular events occurring in bacteroids isolated from nitrogen-fixing root nodules, a 2D gel proteome map was constructed using the total protein extracts from B. japonicum bacteroids 59 . Among the 400 protein spots that could be detected, 180 were identified using MALDI-TOF-MS by searching the available database for B. japonicum. The data showed that the bacteroid expressed a dominant and elaborate network for nitrogen and carbon metabolism, which is closely dependent on the plant-supplied metabolites. Although the B. japonicum genome encodes over 700 genes related to transport, only a number of specific ABC transporters appeared to be expressed in bac-teroids. They also seemed to lack a defined fatty acid and nucleic acid metabolism. Proteins related to protein synthesis, scaffolding, and degradation were among the...

Defence Related Signalling Compounds

No significant oxidative burst was detectable at the time of giant cell induction and at later time points (Melillo et al. 2006 Das et al. 2008). ROS are also produced in host plants during interaction with rhizobia notably in the infection process (Santos et al. 2001). So the bacteria have to protect themselves from these defence molecules and bacterial strains with impaired capacity to detoxify H2O2 have deficiencies in their symbiotic capacities. Despite negative effects, ROS has been reported as signalling molecules in the control of nodulation process, and a threshold level of ROS would be required for a harmonious nodule development (Pauly et al. 2006). Additional major molecules involved in the regulation of the cellular redox state, nitrogen monoxide (NO) and glutathione (GSH) are detected in response to rhizobia and required in proper nodule development (Frendo et al. 2005 del Giudice et al. 2011). Unfortunately, the role of GSH and NO in giant cell...

Glutathione is the cofactor needed in pests metabolism for pesticide resistance

Parasite endogenous glutathione (PEGSH) and the enzymes belonging to its metabolic pathways (especially glutathione -transferases (GST)) are well known to play a role in the detoxification of a range of pesticides (e.g. para-thione and its derivates) and thus are recognized as factors for the resistance of a large variety of pests, mainly insects, and against various pesticides (Nomeir et al. 1987, Shivanandappa and Rajendran 1987, Kirby et al. 1994, Sun et al. 1990, Balabaskaran et al. 1989, Chiangh and Sun 1993, Ku et al. 1994, Suckling et al. 1990, Owusu and Korrike 1996, Sivori et al. 1997, Egaas et al. 1992, Gould and Hodgson 1980, Reidy et al. 1990, Yu 1996). Glutathione transferase is a collective term for the family of predominantly cytosolic isoenzymic proteins found throughout the animal kingdom (Reidy et al. 1990). They act by catalysing the conjugation of a broad range of compounds bearing an electrophilic site with reduced GSH (Reidy et al. 1990). This mechanism is not...

Interpretation Of Transport Data

It should be noted that our efforts to describe the export and emission of scent molecules in quantitative terms might be complicated by (at least) one other factor. The absence of both appreciable internal pools of scent volatiles and the biosynthetic enzymes of such compounds in scent-emitting floral tissue of Jasminum species prompted Watanabe et al.68 to discover that fragrance components are stored as nonvolatile glycosides. However, Loughrin et al.69 found that the level of glycosid-ically bound volatiles in Nicotiana species was not correlated with the emission levels of such volatiles, but with the age of the flower older, senescing flowers had higher levels of stored glycosides. It has been speculated that glycosides are either precursors, storage forms, or detoxification products of scent compounds. The role of these derivatives, as well as their amounts, may depend on plant species and physiology. Hence the (reversible ) formation of glycosides must be regarded side branch...

Ascorbate A Key Player in Leaf Development and Responses to the Environment

The production of superoxide and H2O2 as a result of processes associated with photosynthesis has been described many times previously (Asada, 1999 Foyer and Noctor, 2000, 2003) and will not therefore be discussed here in detail. Chloroplasts contain a hierarchy ofH2O2-detoxificationmechanisms in which ascorbate plays a central role (Noctor and Foyer, 1998 Foyer and Harbinson, 1999 Foyer and Noctor, 2000). Ascorbate also functions in the systems that reduce the probability of ROS generation in the chloroplast, particularly the xanthophyll cycle, in which ascorbate provides the reducing power necessary to convert violaxanthin to zeaxanthin in the de-epoxidation sequence (Demmig-Adams and Adams, 1992 Foyer and Harbinson, 1999). Thus, like the regeneration of tocopherol discussed above, the violaxanthin de-epoxidation reaction oxidizes ascorbic acid in the lumen. Hence, two intrinsic defense processes protecting PS II draw on the lumen ascorbate pool. Since no kinetic evidence has been...

Plant glutathione supports pesticide resistance of parasites

The sulphur status of a plant is a strong influencing factor for GSH concentration in its tissue (Schnug et al. 1995). Consequently higher GSH levels in plants devoured by parasites increase the pests vitality as observed in Epi-lachna species fed on soybean leaves with different S02 fumigations. From these results it has been concluded that air pollution improves the success of pests on crop plants (Hughes and Voland 1988). High amounts of S containing compounds devoured may also improve the vitality of the parasite. According to Capua et al. (1991) mites foraging on Allium sativum, which is well known for its high content of reduced S compounds (Haneklaus et al. 1997), had a higher GST activity. As a consequence of this also the rate of epoxidation (a detoxifying reaction involving GSH) of aldrin was also increased in the parasites. typically higher sulphur concentrations increase GST activity in Spodoptera spec. Consequently, highest in GST was Brassicajuncea (Brassica species are...

Transcriptional Response To Uvb Radiation

An important output of signal transduction pathways involves changes in gene expression. Therefore, the determination of the transcriptional response to a stimulus is instrumental for the characterization of signalling pathways and their interactions. Exposure of plants to UV-B radiation leads to transcriptional activation and repression of a number of genes (Jordan, 2002 Brosche and Strid, 2003, and references therein), including those that might be attributed to protection and defence, such as DNA repair (Ries et al., 2000b), protective pigment synthesis (Logemann et al., 2000 Jenkins et al., 2001), cell cycle (Logemann et al., 1995) and detoxification of reactive oxygen species (Willekens et al., 1994). In most cases it is not yet possible to unequivocally classify induction of particular genes to either damage-mediated or potential UV-B photoreceptor-mediated pathways. However, an initial attempt was made by using as a criterion the level of UV-B required to first detect...

The transcriptional regulation of cold and droughtinducible genes

Transcripts of many genes with different functions are induced by various environmental stresses. The inducible genes can be divided into several groups according to their functions. One group includes genes for signal transduc-tion pathways as we have discussed above. The other genes encode effector proteins such as LEA proteins, enzymes for osmolyte biosynthesis, and detoxification enzymes. Transcription factors regulate the expression of stress-inducible genes through direct binding to conserved cis-elements in the promoter regions of the inducible genes. These cis-elements include the ABA responsive element (ABRE), the dehydration responsive element (DRE) C-repeat (CRT), MYCRS (MYC recognition sequence) MYBRS (MYB recognition sequence), and other sequences. Earlier studies using yeast one-hybrid assays identified several important transcription factors that bind to stress responsive cis-elements (Stockinger et al., 1997 Liu et al., 1998 Choi et al.,

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 cloned from a wide variety of plant species, and include genes encoding proteins targeted to the...

Effects of phenolic acids upon germination of Calluna seed

Since seed of Calluna normally falls directly onto soil enriched in phenolic compounds, phytotoxicity can be experienced from the germination phase onwards. Incorporation of these compounds into agar on which Calluna seed was sown, showed that some can indeed inhibit the germination process (Fig. 4). Salicylic and -methoxybenzoic acids were the most toxic individual acids but, more importantly, the field mixture also produced a 17 inhibition. In the presence of the fungus, however, such an inhibition was almost entirely removed. Thus even before infection takes place, the presence of endophyte mycelium in the environment around the root can lead to detoxification.

Genetic engineering provides a chance for increasing the protection of crop plants against environmental stress

In the preceding chapters, various mechanisms have been described by which a plant protects itself against environmental stresses, such as heat (section 21.2), cold (sections 3.10 and 15.1), drought and soil salinity (Chapter 8 and section 10.4), xenobiotics, heavy metal pollution (section 12.2), and oxygen radical production (sections 3.9 and 3.10). Genetic engineering opens up the prospect of increasing the resistance of cultivated plants to these stresses by overexpression of enzymes involved in the stress responses. Thus, an increase of the number of double bonds in the fatty acids of membrane lipids through genetic engineering has improved the cold tolerance of tobacco (section 15.1). The generation of plants accumulating heavy metals, such as mercury and cadmium, in order to detoxify polluted soils (section 12.2), may have a great future.

Pathogens With Evolved Mechanisms To Counteract Plant Defense Responses

As described previously, plant pathogens evade -gene-mediated resistance by modification of the elicitor proteins either by mutations in, or deletion of, the Avr genes or by (down-)regulation of Avr gene expression. Yet, when the circumvention of elicitor detection fails, or when the elicitor component is essential for virulence, pathogens require mechanisms to subvert the induced plant defense responses. Indeed, plant pathogens counteract plant defenses by secreting enzymes that detoxify defense compounds, including phytoalexins, or use ATP-binding cassette (ABC)-transporters to mediate the efflux of toxic compounds (as reviewed by Idnurm and Howlett, 2001). Moreover, some bacterial pathogens interfere with R-gene-mediated resistance by secreting proteins that mask the presence of a particular AVR effector protein (Ritter and Dangl, 1996).

On Plants Stress Responses

Zinc is the most important micronutrient that is involved both directly and indirectly in the metabolism of ROS as well as protection of structural components of cell against ROS. In leaves of different wheat and rice cultivars, deficient supply of Zn decreased total SOD activity and, more distinctly, CuZn-SOD activity, whereas Mn-SOD activity was not affected by Zn deficiency (Cakmak et al. 1997 Hajiboland 2000). Interestingly, change in the activity of CuZn-SOD could be used for interpreting different susceptibility of various wheat (Yu et al. 1999b) and rice (Hajiboland 2000) genotypes to Zn deficiency (Table 16.2). Zinc may indirectly be required for high activity of the enzymes involved in H2 O2 detoxification. Reports on the effect of Zn deficiency on the activity of CAT, APX and glutathione reductase (GR) are contradictory. Some reports demonstrated increase (Tewari et al. 2008 Hajiboland and Beiramzadeh 2008) and others reduction of their activity under Zn starvation (Yu et...

Variations in Heavy Metal Tolerance in Plants

Tolerance is based on two different strategies (1) to avoid the entry of excess HM into the plants and (2) to achieve effective intracellular detoxification. The main tolerance-related mechanisms are already wellknown, the most important of which include (1) the reduced uptake and or accelerated excretion of HM by the cells, (2) the metal detoxification and compartmentalization, (3) the control of the metal induced oxidative stress, etc. (Vassilev and Nikolova 2010). The scientific interest with respect to the plant tolerance toward HM has become considerably larger in recent years. On the one hand, this is due to possible usage of tolerant plants for phytoreme-diation of soils contaminated by HM (Kulakov et al. 2009), and on the other hand, the interest is a result of the possible wider usage of the plants as model objects for ecotoxicological studies (Hock and Elstner 2005). The number of research papers related to the identification of plants that have high tolerance and...

Equilibrium Models Concentration Ranges and Biological Functions of Metal Ions

Thus, there is negative feedback in the environment metallome system, exactly tantamount to detoxification. For so-called semi-metals some of which also form colloquial complexes, like Sb, Bi, Te, the speciation pathway of biomethylation (Thayer 1995) will remove their electrophilic properties altogether, turning the cations into ligands (donors) of their own, whereas with other elements (Ge, Sn, Pb, Pt, Au, Cd or Hg) acceptor properties are substantially altered (see the data (c and x values, Table 2.3) for R2Sn2+, R3Sn+ and R3Pb+ species) but do not vanish. Of course, redox processes also influence acceptor properties (cp. the data for different oxidation states of V, Fe, Ce or Tl).

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