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Sucrose Cycling In Storage Parenchyma Cells

When arrived in the storage cells, sucrose metabolism is achieved by several different enzymes performing the same or similar reactions and which operate in parallel. The symplastic enzymes directly involved are in direction of sucrose synthesis sucrose-phosphate synthase (SPS) (in concert with sucrose-phosphate phosphatase) and sucrose synthase (SS), and in direction of sucrose breakdown soluble acid invertase (SAI), neutral invertase (NI) and sucrose synthase (SS) (Fig.3). The reaction products, glucose, fructose and UDP-glucose can be recycled to precursors of sucrose synthesis again by hexokinase, phosphoglucoisomerase (PGI) and UDP-glucose pyrophosphorylase (UDPG-PPase). All these enzymes are supposed to be cytosolic with exception of the soluble acid invertase, which is vacuolar. In addition a cell wall bound acid invertase will hydrolyse apoplastic sucrose. The presence of these enzymatic activities in parallel in storage tissue had been already found by the Australian group...

Sucrose to Starch Conversion in Storage Organs

The pathway of starch synthesis in developing storage organs is relatively well understood (Figure 1.3). In all organs apart from cereal endosperms, sucrose entering the storage parenchyma is converted to G6P in the cytosol. In the case of the potato tuber, sucrose delivered by the phloem from source tissue can be metabolised in different ways. It can either be hydrolysed by apoplastic or cytosolic invertase, respectively, resulting in glucose and fructose, or converted into UDP-Glc and fructose by sucrose synthase (SuSy). The prevailing route of sucrose cleavage depends upon the developmental stage of the tuber. At the onset of tuberisation when cell division takes place, hydrolytic degradation of sucrose Figure 1.3 Principle pathway leading to the formation of starch in storage organs. The alternative route of ADPGlc via generation within the cytosol and subsequent uptake into the amyloplast, as it occurs in the endosperm cells of graminaceous species, is shown by dotted arrows....

Increasing yield by increasing sucrosephosphate synthase

Sucrose-phosphate synthase was selected for modification to see if the interaction between the chloroplast and the rest of the plant could be modified to increase yield. Worrel et al (1991) reported on tomatoes transformed with a gene forZea mays SPS with a Rubisco small subunit promoter (SSU-SPS plants). In most cases, these plants did not have increased yields (Galtier et al 1993, Laporte et al 1997, Signora et al 1998), though, in one case, substantially increased yields were observed (Micallef et al 1995). In all cases, area-based photosynthetic rates were the same or only marginally increased at elevated CO,, indicating that the extra SPS modified how the plant handled photosynthate rather than increased the immediate availability of photosynthate. Table 2. Sucrose-phosphate synthase (SPS) activity in control plants and plants transformed with 35S- or SSU-promoted SPS. Table 2. Sucrose-phosphate synthase (SPS) activity in control plants and plants transformed with 35S- or...

Starch and sucrose are the main products of CO2 assimilation in many plants

In most crop plants (e.g., cereals, potato, sugar beet, and rapeseed), carbohydrates are stored in the leaves as starch and exported as sucrose to other parts of the plants such as the roots or growing seeds. CO2 assimilation in the chloroplasts yields triose phosphate, which is transported by the triose phosphate-phosphate translocator (section 1.9) in counter-exchange for phosphate into the cytosol, where it is converted to sucrose, accompanied by the release of inorganic phosphate (Fig. 9.1). It is essential that this phosphate is returned, since phosphate deficiency in the chloroplasts would cause photosynthesis to die down. Part of the triose phosphate generated by photosynthesis is converted in the chloroplasts to starch, serving primarily as a reserve for the following night period.

Sucrose synthesis takes place in the cytosol

The synthesis of sucrose, a disaccharide of glucose and fructose (Fig. 9.13), takes place in the cytosol of the mesophyll cells. As in starch synthesis, the glucose residue is activated as nucleoside diphosphate-glucose, although in this case via UDP-glucose pyrophosphorylase In contrast to the chloroplast stroma, a pyrophosphatase is not present in the cytosol of mesophyll cells. Since pyrophosphate cannot be withdrawn from the equilibrium, the UDP-glucose pyrophosphorylase reaction is reversible. Sucrose phosphate synthase (abbreviated SPS, Fig. 9.13) catalyzes the transfer of the glucose residue from UDP-glucose to fructose 6-phosphate forming sucrose 6-phosphate. Sucrose phosphate phosphatase, forming an enzyme complex together with SPS, hydrolyzes sucrose 6-phos-phate, thus withdrawing it from the sucrose phosphate synthase reaction equilibrium. Therefore, the overall reaction of sucrose synthesis is an irreversible process. In addition to sucrose phosphate synthase, plants also...

Sucrose transporters DSTs

In plants, SoSUT1 (Spinacia oleracea Sucrose Transporter 1) was the first disaccharide transporter (DST) functionally characterized in a yeast mutant deleted for invertase and expressing sucrose synthase (Riesmeier et al. 1992). DSTs genes, which belong to small multigenic families with 9 members in Arabidopsis and 4 in tomato for instance, encode for a 55 kD polypeptide (Arabidopsis Genome Initiative 2000, Delrot et al. 2001, Sauer et al. 2004, Hackel et al. 2006). Plant DSTs can be clustered into 4 groups regarding their protein sequence homologies group 1 and group 2 are exclusively composed by Group 3 transporters have been reported to localize all along the sieve element and have been proposed to sense the sucrose flux through the plasma membrane (Schulze et al. 2000). Group 4 sucrose transporters are low affinity high capacity transporters (LAHC) localized in the membranes of minor veins of source leaves (Weise et al. 2000). However, their subcellular localization is...

Endocytic Uptake of Solutes and Sucrose into Suspension Plant Cells

That a portion of the nutrients stored in the vacuole are taken up by endo-cytosis was recently established using sycamore cell cultures in conjunction with the endocytic inhibitors wortmannin and LY294002, and Lucifer Yellow as the fluid-phase endocytosis marker (Etxeberria et al. 2005a). When transferred into a sucrose-rich medium, cells accumulated sucrose rapidly for approximately 60 min. Sucrose uptake during this period proved to be wortmannin and LY294002 insensitive. After 90 min incubation, the rate of sucrose uptake increased rapidly in a linear manner for an additional 6 h. This second phase was strongly suppressed by the endocytic inhibitors wortmannin and LY294002, which would be in conformity with the existence of an endo-cytic transport of sucrose into the cells. Complete cessation of sucrose uptake by wortmannin occurred at a time when sucrose had already commenced to accumulate rapidly, this strongly substantiates these observations. Possible involvement of...

Sucrose Biosynthesis in Source Leaves

As outlined in the previous section, triose-P leaving the Calvin-Benson cycle can be exported from the plastid into the cytosol via the TPT and is then distributed between glycolysis and amino acid, lipid and sucrose synthesis (Figure 1.1). Sucrose is the major transport form of photoassimilates in higher plants, and as such forms the interface between pho-tosynthetically active source tissue and heterotrophic sink tissue, where it serves as an energy source for growth and provides building blocks for storage metabolism. During the light period, sucrose synthesis proceeds from triose-P and comprises seven enzymatic steps. The entry molecule is fructose-1,6-bisphosphate (FBP), which is formed by the condensation of two molecules of triose-P catalysed by the enzyme aldolase. In a subsequent reaction, a phosphate group is removed from the C1 atom of FBP by the cytosolic isoform of fructose-1,6-bisphosphatase (cytFBPase) to yield fructose-6-phosphate (F6P). This reaction is essentially...

Sucrose Transport In The Sugar Beet Plant

Sucrose Proton Symporter

Sucrose transport is critical for development and growth in most plant species. Biological membranes like the plasma membrane and the tonoplast are almost impermeable to uncharged and charged molecules under normal conditions unless there is a principle realised within these membranes rendering them selectively permeable to certain molecule species. Some specific sort of pores and or transport proteins have to be present to ensure selective permeability of these membranes for sucrose as well. Once sucrose has been formed within the cytosol of source (net exporting leaf mesophyll) cells, sucrose should be transported through membranes at different stages (fig. 1) 1) Sucrose may be transiently stored within the vacuoles of source leaf cells. Some tonoplast bound transport system for sucrose should be present. 2) Sucrose must cross the plasma membrane of source cells to enter the apoplasm via some transmembrane transport or exocytosis like process if it is not symplastically transported...

Photosynthesis Sucrose Flux Starch Pod Flower Number Soybean

Egli, D.B. and Bruening, W.P. (2001) Source-sink relationships, seed sucrose levels and seed growth rates in soybean. Annals of Botany 88, 235-242. Egli, D.B. and Bruening, W.P. (2004) Water stress, photosynthesis, seed sucrose levels and seed growth in soybean. Journal of Agricultural Science 142, 1-8. Goldschmidt, E.E. and Huber, S.C. (1992) Regulation of photosynthesis by end-product accumulation in leaves of plants storing starch, sucrose, and hexose sugars. Plant Physiology 99, 1443-1448.

The Pathway From Sucrose To Starch

3.2 Sucrose synthase We studied the expression of three isogenes encoding SuSl, SuS2 and SuS3 at the transcriptional level at different stages of seed maturation and in different rice organs (22). It has revealed that, although all of them are expressed mainly in seed, the expression of Susl is ubiquitous while that of Sus3 is exclusive in seed, and the expression sites and strengths of Sus2 seem to complement those of Susl, especially under the stress conditions such as anaerobiosis. The expression of Susl is quite unique it is upregulated by the availability of sucrose. These findings imply that Susl and Sus2 are house-keeping genes while Sus3 bears a specific role in the grain filling with starch. Sucrose is transported into sink organs form leaves through phloem. Enzymes located in phloem might regulate the sucrose concentration to force the sucrose flow from source to sink. Immunoblotting of SuSl and SuS2 in the extract of either shoot or root of etiolated seedling showed that...

Involved In Sucrose Metabolism

Since it had been found in the 1960s that wild forms of sugarcane and high-yield commercial varieties are distinguished by different enzyme activities of sucrose metabolism (3), a correlation between sucrose storage (or sucrose concentration in the internodes) and enzyme activities was sought for. As pointed out before (Fig.3), sucrose undergoes a cycle of synthesis and breakdown. In theory, sucrose concentration can be increased by shifting up sucrose synthesis activity or by switching down the sucrose hydrolysis activity, whereby each of these metabolic reactions is catalysed by different enzymes in parallel, not considering even that each of these enzymes most likely is comprising a family of genes. Zhu et al. (20) analysed the progeny of a defined cross between Saccharum officinarum and Saccharum robustum and followed sucrose concentration and enzyme activities during internode ripening of low and high sucrose clones. The best correlation found, comprising all internodes and all...

Sucrose as a Maturation Signal

Sucrose has a dual function as a transport and nutrient sugar and as a signal molecule triggering storage-associated processes (Smeekens 2000 Koch 2004). Increasing sucrose concentration in Vicia and pea cotyledons, as well as the barley endosperm at the onset of maturation, is mediated by sucrose transporter activity within newly established epidermal endospermal transfer cells (Weber et al. 1997b Tegeder et al. 1999 Weschke et al. 2000). It marks the switch from maternal to filial control of seed growth. In Vicia and barley, sucrose induces storage-associated gene expression and at the transcriptional level up-regulates enzymes like sucrose synthase and ADP-glucose pyrophosphorylase (AGP Heim et al. 1993 Weber et al. 1998b Weschke et al. 2000). In vitro sucrose feeding disrupts the meristematic state, induces cell expansion and endopolyploidization (Weber et al. 1996) and promotes cotyledonary storage activity at the transcript level (Ambrose et al. 1987 Corke et al. 1990). In...

Transport Of Sucrose

Proton Translocator

Once sucrose is synthesized in mesophyll cells of source leaves, it has to be translocated to sink tissues. This transport occurs through phloem which contains elongated cells joined by sieve plates, consisting of diagonal cell walls perforated by pores. The single cells called sieve elements are surrounded by companion cells. Sieve elements and companion cells, in turn are connected to each other by many plasmodesmata. Photoassimilates generated in mesophyll cells diffuse via plasmodesmata to the phloem parenchyma cells. The further transport of photoassimilates from the phloem parenchyma cells to the sieve tubes can occur symplastically via plasmodesmata without involving translocators or apoplastically in which photoassimilates are first transported from the source cells via the phloem parenchyma cells to the extracellular compartment, the apoplast. This export does not require any energy as the concentration of sucrose is much higher in source cells than in the apoplast. The...

Sucrose Synthesis

As in many higher plant species, sucrose plays the main role in growth and development of sugar beets. Because of its non reducing nature, sucrose is considered as the major transport and storage form of sugars in many plant species (9), especially in economically important crop plants such as sugar cane, carrots, melon, sucrose storing tomato varieties and beet roots (fodder beet, red beet, sugar beet). In general, photosynthetically fixed carbon is converted to sucrose within the cytoplasm of source leaves and then exported through the phloem to photosynthetic growing and non photosynthetic sinks of the plant like sink leaves, flowers, tubers, roots or fruit for sustaining growth and or for intermediary or long term storage. Normally the triose phosphate translocator mediates export of the primary photosynthesis products from the chloroplasts into the cytosol (10). This transporter is an integral membrane protein localised at the inner envelope membrane of chloroplasts whereas the...

Sucrose X

And transport through membranes are closely interacting to achieve the final goal , namely high sucrose concentrations. The review here focussed only on sucrose metabolism and transport, it fully neglected the influence of other nutrient and environmental factors on sucrose yield. However, as long as there is no clearcut picture of what happens to sucrose itself, no mechanistic model of influence by other factors can be reasonably developed. Therefore, focus on sucrose may be justified. Definitely, the future will lie in bringing together physiological mechanisms and agronomic factors to compose a whole plant model and to reveal quantitatively the network of metabolism, transport, growth and nutrition. Sugarcane is an interesting plant for plant physiologists in general, it hopefully may again give rise to new basic knowledge on plant function, as it happened when C-4 photosynthesis had been detected first in sugarcane. But research on the physiology of sucrose storage also has...

Methods and Molecular Tools for Studying Endocytosis in Plantsan Overview

Abstract Proteins of the endocytosis machinery in plants, such as clathrin and adaptor proteins, were isolated and characterized using combinations of molecular biological (cloning and tagging) and biochemical methods (gel filtration, pull-down assays, surface plasmon resonance and immunoblotting). Other biochemical methods, such as cell fractionation and sucrose density gradients, were applied in order to isolate and further characterize clathrin-coated vesicles and endosomes in plants. Endocytosis was visualized in plant cells by using both non-fluorescent and fluorescent markers, and by employing antibodies raised against endosomal proteins or green fluorescent protein-tagged endocytic proteins in combination with diverse microscopic techniques, including con-focal laser scanning microscopy and electron microscopy. Genetic and cell biological approaches were used together to address the role of a few proteins potentially involved in endocytosis. Additionally, biochemical and or...

Isolation of Clathrin Coated Vesicles

Plant clathrin-coated vesicles (CCVs) were isolated from cucumber and zucchini hypocotyls (Depta et al., 1991 Holstein et al., 1994). CCV components were protected against proteolysis using homogenization media composed of 0.1 M MES (pH 6.4), 1 mM EGTA, 3 mM EDTA, 0.5 mM MgCl2, a mixture of proteinase inhibitors and 2 (w v) fatty-acid-free BSA (Holstein et al., 1994). The crude CCV fraction (40 000-120 000 g pellet) was further purified by cen-trifugation in Ficoll sucrose according to Campbell et al., (1983) and then by isopycnic centrifugation in a sucrose density gradient using a vertical rotor (160 000 g, 2.5 h, Depta et al., 1991). CCV-enriched fractions (collected at 40-45 sucrose) were removed, pooled and pelleted. CCV fractions were stored at - 80 C for further use. Immunoblotting was performed using monoclonal antibodies against mammalian adaptins and clathrin. Confirmation of the presence of a P-type adaptin in plants was provided by dot and Southern blotting experiments...

Osmotic Adjustments and Controlling Factors

Intracellular water lost from the cell due to salt, drought and cold, leads to cellular dehydration. To prevent this and protect the cellular proteins, plants accumulate many organic compounds such as amino acids (proline), quaternary and other amines (glycine betaine and polyamines), a variety of sugars (mainly fructose and sucrose), sugar alcohols, complex sugars (like trehalose and fructans) and organic acids (oxalate, malate) (Valliyodan and Nguyen 2006). These metabolites with osmolytic function are also known as compatible solutes or osmoprotectants and may accumulate to high levels without disturbing the intracellular biochemistry (Ford 1984). By reducing the water potential within the cell, water loss is prevented and osmotic adjustment is facilitated (Delauney and Verma 1993).

Seed Research a Brief History

Gregor Mendel's studies on pea plants incorporated several seed traits, including the occurrence of wrinkled (rugosus) peas with a recessive mutation in the r locus. It is now known that the primary lesion in this locus results in rr embryos lacking starch branching enzyme I (SBEI) activity hence less amylopectin is synthesized during seed development, a build-up of sucrose and water ensues, and the embryo, which contains less than its full complement of reserves, shrinks during maturation drying (Wang and Hedley, 1991). The pioneering work of Mendel (1822-1884) also has an interesting tie-in with the pioneering work of Nobel laureate Barbara McClintock (1902-1992) almost a century later, which initially, like his own studies, was largely ignored. She discovered the transposable element, or 'jumping gene', and contended that certain autonomous elements within the maize gene are able to excise and become reincorporated into DNA elsewhere, resulting in a mutant allele (McClintock,...

Various transport processes facilitate the exchange of metabolites between different compartments

Sucrose transported across the membrane against the concentration gradient. An example of this is the accumulation of malate in the vacuole (Figure 1.21C see also Chapter 8). Another example of secondary active transport is the transport of sucrose via an H+-sucrose symport in which a proton gradient, formed by primary active transport, drives the accumulation of sucrose (Figure 1.21C). This transport plays an important role in loading sieve tubes with sucrose (Chapter 13).

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...

Conventional IEF in Soluble Amphoteric Buffers

CA-IEF was born as a preparative technique in a liquid phase, exploiting large-size columns filled with a sucrose density gradient as an anticonvective medium. When reports appeared on its use in PAG strips or thin tubes 20 , its popularity grew exponentially untill it became a household item in every lab. Although there are four major commercial brands available today, the formulas and general properties of only three of them are known Servalyt, Ampholine, and Pharmalyte (Figure 2.3), with the Bio-Lyte product (from Bio-Rad) being undisclosed. It can be seen that Ampholine, still made according to the original patent by Vesterberg 3 , comprises aliphatic oligoamino oligocarboxylic acids, obtained by reacting mixtures of oligoamines (3 to 9 nitrogen long) with unsaturated acids, such as acrylic and itaconic acids. Servalyt is made by first preparing oligoamines via reaction of ethylene imine with propylene diamine and collecting by distillation all products up to 400 Da in size. Such...

The mechanisms regulating NO3 uptake

Experimentally, NO3- uptake can be increased in parallel with the growth rate by increasing light intensity (e.g. Gastal and Saugier 1989). The diurnal regulation of NO3- uptake (higher rate during the light period, lower rate during the dark period) has been considered as a specific example of its regulation by light (Delhon et al. 1995). The stimulation of NO3- uptake by light is attributed to photosynthesis, since it could be prevented by decreasing the atmospheric CO2 concentration (Delhon et al. 1996). Moreover, the addition of carbohydrates to the nutrient solution is known to increase NO3- uptake (Hanisch Ten Cate and Breteler 1981). Blocking phloem translocation in soybean plants by means of stem girdling led to a decline in the rate of NO3- uptake, which is partially restored by adding glucose to the nutrient solution (Delhon et al. 1996). No consensus exists that an energetic shortage might occur in roots, even at night, and an increased energisation of the plasma membrane...

Results and Discussion

Two-phase partitioning, sucrose density gradient centrifugation, and GFP imaging were used to investigate the subcellular localization of CmERS 1. The results demonstrate that CmERSl is predominantly localized to the ER (Fig. 1). Our data provide experimental evidence for the ER localization of an ERS-type receptor. These observations, together with the ER localization of AtETR1, support the deduction that the ER may play a central role in ethylene perception and early signal transduction (Chen et al., 2002 Gao et al., 2003).

The VAZ Pathways Story

Of course, the instrumentation and analytical methods available 45 years ago were crude by today's standards. I used preparative columns packed with powdered sugar to separate the xanthophylls of saponified extracts of leaves. Saponification removed chlorophyll that these columns could not resolve from xan-thophylls. To assure complete recovery of xanthophylls after saponification, the xanthophylls were washed into ethyl ether instead of petroleum ether. Safety precautions were not what they are today and I was lucky not

Keeping It Simple Why Unicells Are Cool

Many of the abovementioned limitations do not apply to unicellular photosyn-thetic organisms, such as algae, and the compartmentation issue can be addressed by investigation of prokaryotic photosynthetic organisms, such as cyanobacteria which are evolutionary connected to plastids and thus might serve as models for plastid metabolism. A prime example for the dissection of a relatively complex metabolic pathway in photosynthetic organisms is the reductive pentose phosphate pathway, also known as the Calvin cycle. In series of milestone papers in the late 1940s and early 1950s, using unicellular algae such as Scenedesmus and Chlorella, as well as land plant leaves, the path of carbon in photosynthesis was elucidated. In a landmark paper, it was shown that the first labeled organic carbon compound found in Scenedesmus cells that were allowed to photosynthesize in the presence of labeled carbon dioxide for five seconds was phosphoglyceric acid and that the first free carbohydrate to...

Concepts And Definitions

Ideally, photoautotrophic micropropagation should be segregated from sugar-free micropropagation. However, in this chapter, while we will define photoautotrophy as the plant nutritional type where only endogenous carbohydrate is used as the energy source, for all practical purposes photoautotrophic micropropagation refers to micropropagation with no sugar added to the medium. Sugars and other carbohydrates may be significant components of agar and other gelling agents, but perhaps it is reasonable not to consider it as an exogenous carbohydrate source in the practical definition of photoautotrophic micropropagation.

Transcellular Osmosis and Polar Water Permeability

Sucrose solution, water moves transcellularly from chamber A to chamber B. The rate of the flow is proportional to the osmotic pressure (po) in B. The TCO constant (K) defined by Kamiya and Tazawa (1956) is obtained by dividing the initial rate of water flow (Jv) by the external osmotic pressure (po) that drives the flow. Namely, Later, Dainty and Ginzburg (1964a) found in Chara that hydraulic conductivity decreased markedly with an increase in the external sucrose concentration. They found that the inhibitory effect of the external osmolality cannot be attributed to the sweeping away effect. The inhibitory effect of the external osmotic pressure on hydraulic conductivity was reconfirmed by Kiyosawa and Tazawa (1972) in Nitella flexilis.

SOS Genes and Salt Tolerance

The salt overly sensitive (SOS) ion homeostasis and signaling pathway is another well-characterized abiotic stress response in Arabidopsis. The SOS1, SOS2, and SOS3 loci were first identified through forward genetic screens for salt-hypersensitive growth. SOS1 is a plasma membrane Na+ H+ antiporter that is essential for Na+ efflux from roots. SOS2 belongs to subgroup 3 of the sucrose non-fermenting-related kinases (SnRK3s). SOS3 is a myristoylated calcium-binding protein that likely responds to salt-induced Ca2+ oscillations in the cytosol. The SOS signaling pathway functions in regulating Na+ homeostasis and salt tolerance in Arabidopsis. High Na+ stress triggers a calcium signal that activates the SOS3-SOS2 protein kinase complex, which then stimulates the Na+ H+ exchange activity of SOS1 at the plasma membrane. SOS2 also activates Na+ H+ (AtNHX) exchangers on the vacu-olar membrane (Zhang et al. 2004b). Increased expression of the Arabidopsis tonoplast membrane Na+ H+ antiporter,...

The Biochemical CO2 Pump of C4 Photosynthesis Share of Labor Between Two Cell Types Causing Massive Flux of Metabolic

CO2 fixation by Rubisco in bundle sheath cells yields two molecules of phospho-glycerate (3-PGA). The reduction of two 3-PGA to two triose phosphates requires two NADPH. However, the oxidative decarboxylation of one malate yields only one NADPH (and linear electron transport is insignificant in bundle sheath cells), hence one molecule of 3-PGA has to be exported to the MC plastids where it can be reduced to triosephosphate (TP). Two thirds of the generated triosephosphate then need to be re-exported to bundle sheath plastids for regeneration of ribulose-1,5-bisphosphate the remainder can be exported as sucrose to sink tissues.

Higher Level Control of Organ Size and Plant Wide Integration

Changing not the number of developing sink organs but their sink strength can also influence their final size apoplastic expression of a yeast invertase, which cleaves sucrose into glucose and fructose and is thought to influence sink strength, was found to increase tuber size in potato tubers (Sonnewald et al. 1997). However, the effect was compartment-specific, and targeting in-vertase to the cytosol actually had the opposite effect.

Primary Metabolites Of Carum Carvi

Mono-, oligo- and polysaccharides found in all parts of the plant serve as a temporary reserve material. The monosaccharides identified in caraway fruits, leaves and spare tissues are hexoses glucose and fructose. Main reserve disaccharide is saccharose (sucrose), found in quantity 1 and 3 of fresh plant weight in fruits and leaves respectively. The changes in main mono- and disaccharides content during caraway two years vegetation period is described in details by Hopf and Kandler (1976). Other disaccharides found in the seeds in minor amounts are trehalose, glucosyl mannose and mannityl-1- -glucose. The most interesting trisaccharide of Carum is perhaps umbelliferose (Figure 1a), an isoraffinose typical to umbellifers, found in all parts of the plant and serving as a temporary reserve material similar to sucrose. It occurs in greater amounts than sucrose only in the ripe fruits and is not preferentially accumulated in any particular vegetative organ. Physiology of this sugar, its...

By the Inner Cortex Cells Located near the Unloading Phloem Elements

Heterotrophic plant cells, such as root and suspension culture cells, as well as dark-grown plant cells are dependent on external nutrient supply. Sucrose starvation induces autophagy and formation of autolysosomes in plant cells (Yano et al. 2004). Within the plant body, phloem elements redistribute assimilates synthesized in leaves and transport them towards sink tissues. One of the best studied sink tissues is that of root apices. In root apices, unloading phloem elements release large amounts of sucrose, literally flooding the neighboring cells. Sucrose is transported from cell-to-cell symplastically via plasmodesmata (Oparka and Cruz 2000 Baluska et al. 2001c, Sadler et al. 2005). However, calculations made for maize root apices revealed, that the number of plasmodesmata can not satisfy the high demand for sucrose established by their large meristems and by the root caps (Bret-Harte and Silk 1995). Another popular scenario is that sucrose is enzymatically cleaved by cell wall...

In vitro conservation

Geetha etal. (1995) and Nirmal Babu et al. (1994, 1999a,b) reported conservation of cardamom germplasm in in vitro gene bank by slow growth. The above workers carried out various trials to achieve an ideal culture condition under which the growth is slowed down to the minimum without affecting the physiology or genetical make up of the plant. The slow growth is achieved by the incorporation of agents for increasing the osmotic potential of the medium, such as mannitol. They found that half strength MS without growth regulators and with 10 mg l each of sucrose and mannitol was the best for in vitro storage of cardamom under slow growth. By using the above medium in screw capped vials the subculture interval could be extended to one year or more, when incubated in 22 2 C at 2500 lux of light and at 10 h photoperiod. Low temperature storage at 5 C and 10 C was found to be lethal for cardamom, as the cultures did not last more than three weeks (Geetha et al. 1995).

Crucial First Step in Establishing Chloroplast Cytoplasm Metabolic Connection Evolution of the Triose Phosphate

Considering the situation of a free-living, coccal cyanobacterium, the presence of a triosephosphate phosphate antiporter in its plasma membrane would very likely have been detrimental because it would have allowed for the efflux of triose phosphates from the cyanobacterium in the presence of suitable external concentrations of orthophosphate. It is thus reasonable to hypothesize that the triosephos-phate phosphate antiporter was not introduced by endosymbiotic gene transfer from the cyanobacterium, but it was derived from a pre-existing host protein that was directed to the cyanobacterial plasma membrane (now the inner plastid envelope membrane) after the endosymbiont had entered the host cell. This hypothesis was recently tested by phylogenomic and phylogenetic analysis of genomic and EST-sequence data from a broad range of organisms. It was shown that the plastidial triosephosphate phosphate translocators evolved from transport proteins of the eukaryotic endomembrane system,...

Composition of the Medium

Sucrose is the most common carbon source in culture media, although the percentage used with different species varies and is generally determined by empirical manipulation of one or a combination of the existing culture media. Basal media such as MS (Murashige and Skoog 1962) or NLN media (Lichter 1982) with slight modifications are commonly used with Brassica and other species. With cereals, media such as A2 (Touraev et al. 1996b) and MMS3 (Hu and Kasha 1997) are also used. Nitrogen, phosphorus and calcium sources are also adjusted in these media. As for mineral micronutrients, it has been shown recently that copper sulphate increases the percentage of green plant regeneration in the very responsive winter-barley cultivar Igri (Wojnarowicz et al. 2002). Studies with this cultivar have also shown a marked short- and long-term influence of iron in the culture medium on isolated microspores used for embryogenesis. Quite frequently, the same composition adjusted for anther culture is...

Current Work In Our Laboratory Isolation of Fungal Effector Molecules

Stage aimed at interfering with the adhesion between the plant cell wall and plasma membrane, which is required for the expression of wall-associated responses. In order to identify the fungal molecule(s) responsible for this effect, we are using a Saccharomyces cerevisiae-based signal sequence trap technique in which 5' enriched cDNAs from developing rust fungal basidiospores are fused in frame with a truncated yeast invertase lacking an initiator methionine and signal sequence. cDNAs encoding the N-termini of proteins capable of directing this fusion protein to the secretory pathway are selected for because of their ability to allow an invertase-deficient strain of yeast to grow on sucrose medium and are likely to encode proteins relevant to the initial pathogenesis process, including the adhesion-reducing mole-cule(s). This screen may also be helpful in cloning peptide cell death elicitors produced by the cowpea rust fungus (D'Silva and Heath, 1997) that are produced following...

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.

Are fruits of the same size and color different in irondeficient and control plants

A recent paper has provided evidence that the chemical composition of peach fruits having the same size, color and firmness, but coming from Fe-deficient and Fe-sufficient trees, is indeed different (Alvarez-Fernandez et al., 2003a). Both types of fruits had similar H+ titratable acidity ratios, suggesting that maturity was similar. The major finding in this study was a change in the total sugars to total organic acids (w w) ratio, which decreased significantly with Fe deficiency, from 12 to 9 in the cultivar 'Carson' and from 10 to 7 in the cultivar 'Babygold' (Figure 4-3 Alvarez-Fernandez et al., 2003a). This change would likely modify the organoleptic characteristics of fruits, probably decreasing the value of the crop. In both cultivars, Fe deficiency generally caused moderate increases in organic anion concentrations, which were larger for succinate and quinate (35-52 and 33-48 , respectively), than for citrate and malate (17-20 and 11-12 , respectively Alvarez-Fernandez et al.,...

Size Control of the Proximal Root Apical Meristem and the Mitotic Cell Cycle

Modulates the onset of endoreduplication (Schnittger et al. 2002a Boudolf et al. 2004, 2009). CCS52A1, an activator of the anaphase complex, is able to target CYCA2 3, a mitotic cyclin, for destruction in the elongation zone of the root (Boudolf et al. 2009) and elevating CYCA2 3 levels delayed the onset of cell elongation (Ishida et al. 2010). These arguments indicate that mechanisms associated with the G2-M transition are putative targets for elongation onset pathways to interfere with the cell cycle. Nevertheless, this does not exclude that factors involved in the G1-S transition that prime cells for a mitotic division by linking the different cell cycle phases are important targets. Indeed G1 cyclins, such as D-type cyclins, are able to stimulate the G1-S transition and to prime cells for a mitotic cell cycle (Schnittger et al. 2002b Dewitte et al. 2003, 2007 Qi and John 2007), thereby preventing endocycles and elongation. In this respect, one link to the core cell cycle machinery...

Sugar sensing and response

G proteins also have a role in sugar transport. A Golgi-localized hexose transporter, suppressor of G p (SGB1), was identified from a genetic screen for AGB1 modifiers that could suppress the altered cell division in the hypocotyl and glucose hypersensitivity of the agbl-2 mutant (Wang et al., 2006a). SGBl has a similar tissue expression pattern as that of AGBl, and its expression increases in the presence of D-glucose or sucrose. Interestingly, in the absence of exogenous sugar, SGB1 traffics to small vesicular compartments suggestive of the trans-Golgi network and the addition of sugar collapses these vesicles to the Golgi proper. Loss-of-function mutants of SGBl phenocopy agbl-2 mutants, whereas overexpression of SGBl suppresses the cell division and sugar hypersensitivity of agbl-2 mutants. These findings provide genetic evidence that SGB1 acts together with AGB1 in regulating sugar transport. These findings establish SGB1 as the first potential effector protein for AGB1, although...

Genetics and Physiology of the Floral Transition

Further, nutrition also has an impact on flowering time. It is known that sucrose has an effect in Arabidopsis. High levels of sucrose cause a delay of the transition to the reproductive phase, allowing for more meristems to be allocated to further growth (Ohto et al, 2001). In most cases, different types of stress shorten the time to flowering. It is not known till date whether these factors act through one of the described pathways or if there are additional unidentified pathways.

Sink Strength In Sugar Beet

The old source leaves supply predominantly the core region, whereas the youngest source leaves supply first of all the outer regions of the beet root with photoassimilates and nitrogen (140). The phloem parenchyma and meristematic cells of the supernumerary cambia are served first because of their vicinity to the phloem elements, the large storage parenchyma cells between the cambia are served relatively late, the core region of a beet root is served latest. However, since the core region is supplied over the longest time period, the sugar content is highest in this region (28, and literature cited therein). Consequently, increase in cell number, cell growth and accumulation of sucrose are the minimum stages characterising the beet taproot as a sink.

Conclusion And Future Strategies

With regard to sucrose accumulation in beetroots, not only the sucrose metabolising enzymes such as SuSy and SPS have to be considered in future experiments on the molecular genetics level as factors determining sink strength and sucrose accumulation capacity. In analogy to the situation at the source site, future experiments down to the molecular genetics level (including the generation of transgenic plants) should pay attention to the possible influence of cell wall bound acid invertase within the different sink tissue regions, the influence of the number (and specific activity) of the plasmalemma and tonoplast bound sugar transporters and the influence of hormonal control over their development as well as of sugar sensing. An important tool in this regard could be the comparison of different subspecies of Beta vulgaris, e.g. vulgaris var. alba (fodder beet, 3-5 sucrose) vs. altissima (sugar beet, 15-20 sucrose) or even of sugar beet with the presumed mother Beta vulgaris ssp....

Subcellular Localization of BP80 and its Homologues

Investigations on the location of BP-80 and its homologues have also been performed on non-storage protein producing cells. Immunogold electron microscopy and subcellular fractionation approaches have shown that VSR proteins are not present in the vacuolar membrane (Ahmed et al. 1997 Paris et al. 1997 Sanderfoot et al. 1998). BP-80 has been localized to the Golgi apparatus and to a putative lytic PVC in pea root tip cells (Paris et al. 1997). AtELP, a BP-80 homolog from Arabidopsis equivalent to VSRAt1 (Ahmed et al. 1997) has been localized to the Golgi apparatus and to a putative PVC characterized by 100 nm diameter tubules in Arabidopsis root tip cells (Sanderfoot et al. 1998). However, these tubular structures were also consistent with the appearance of TGN (Robinson et al. 2000). Subcellular fractionation demonstrated that AtELP in both Arabidopsis (Ahmed et al. 1997 Sanderfoot et al. 1998) and transgenic Arabidopsis plants expressing a mammalian Golgi enzyme...

Increased Content of Atmospheric CO2

For a number of species, results have shown that photosynthesis is increased by an elevation of atmospheric CO2 (Poorter and Navas 2003 Long et al. 2004 Ainsworth and Long 2005). The degree of photosynthetic amelioration depends on interaction with other factors such as temperature (Turnbull et al. 2002) and nutrient availability (Kruse et al. 2003). In growing leaves, assimilation is often stimulated more strongly than in fully differentiated leaves (Pearson and Brooks 1995 Miller et al. 1997 Wait et al. 1999), which leads to increasing contents of starch, sucrose, glucose and fructose (Poorter et al. 1997). If plants are exposed to elevated CO2 for a longer time, acclimation is observed and assimilation decreases gradually (Stitt 1991 Ainsworth et al. 2003). Growth usually reacts in a less-pronounced way towards elevated CO2, but data reported in the literature shows an enormous variability (Poorter and Navas 2003). Similar to biomass growth, crop yield from studies under elevated...

SNF1Related Protein Kinase 1 SnRK1

The sucrose synthase gene that is expressed in potato tubers is SUS4 (Fu and Park 1995). Under normal conditions, it is expressed only in tubers but its expression can be induced in leaves in response to incubation with high concentrations of sucrose (Fu and Park 1995) its expression is not affected at all by glucose. Purcell et al. (1998) reported that expression of SUS4 required the activity of a regulatory protein kinase called sucrose nonfermenting-1-related protein kinase 1 (SnRK1). This protein kinase was shown subsequently to be required for the redox modulation Fig. 4.3 The relative activities of sucrose synthase and invertase in potato tubers determine how much carbon enters the storage pathway for starch biosynthesis and how much enters the glycolytic pathway. The starch biosynthesis pathway is controlled by the metabolic regulator, SnRKl (McKibbin et al. 2006) Fig. 4.3 The relative activities of sucrose synthase and invertase in potato tubers determine how much carbon...

General Anatomical Characteristics Of In Vitro Plants

Generally, anatomical characteristics especially the leaf anatomy of in vitro plants grown in the conventional micropropagation system has been studied intensively in the last few years. Conventionally, micropropagation is carried away using small, relatively airtight culture vessels containing nutrient media with 20-30 g L-1 sucrose (as a carbon source for the plantlets) and under a low PPF of about 30-80 mol

Applications in Biotechnology

Free sugars are desirable in some crops, the obvious examples being sugar beet and sugar cane. The enzymes targeted by breeders and biotechnologists in this case are those that make sucrose, i.e. SPS and sucrose phosphate phosphatase (SPP), and those that break it down, i.e. sucrose synthase and invertase. Once again, a trait that has been a target for many years for food crops has received new impetus as the biofuel market has become established. Sugar cane producers, in particular, who have been shut out of the European market by import tariffs and the effect of subsidies given to Europe's sugar beet farmers, are now seeing their profit margins increasing at last, and biotechnology companies are again turning their attention to a crop in which previously it may not have been worth investing.

Pathogenesisrelated Proteins

Classes of defence stress-related identified proteins include protease inhibitors peroxidase, proteomase and carboxylase. Many unique nodule proteins have been revealed for the first time (Wienkoop and Saalbach, 2003). Some proteins are not under the influence of signalling pathways such as activation of MMP2 protein is not dependent on salicylic acid or jasmonic acid (JA) signalling pathways. Proteins not identified in the previous proteo-mic studies of nodules include halo acid dehalogenase-like family, which has a sequence similar to sucrose-6-phosphate phosphohydrolase and a sequence from Arabidopsis that has halo acid dehalogenase-like domain, osmotin-like protein precursor, UVB resistance protein-like protein, thaumatin-like protein PR-5b and MHN13. The last one (MHN13), identified in M. trancatula (Gamas et al., 1998), is closely related to the PR10 family unlike some other members of the PR10 family found in M. trancatula, such as MtPR10-1, which is constitutively expressed in...

Carbon nutrition of mycorrhizal fungi A External organic carbon sources

The very limited in vitro growth of hyphae from germinated spores of arbuscular mycorrhizal fungi may be somewhat stimulated by addition of nutrients to the medium. Although some early work indicated that sugars are inhibitory or non-stimulatory (see Hepper, 1987), it now appears that sucrose and glucose can be stimulatory at low concentrations (Siqueira et al., 1982 Carr et al., 1985 Siqueira and Hubbell, 1985). The optimum levels for stimulation of around 2 gkg ' fresh wt are similar to the concentrations of ethanol-soluble carbohydrates recorded in mycorrhizal leek roots (Amijee et al., 1990).

Low Nutritive Quality Of Douglasfir Foliage

Likewise, Douglas-fir trees resistant to budworm defoliation had higher levels of sugars in their foliage than susceptible trees at all three sites (Clancy, 2001). This is in agreement with results from artificial diet bioassays budworm fitness was best on artificial diets with sugar (i.e., sucrose) concentrations of 6 dry weight, which is near the lower limit observed for Douglas-fir foliage (Clancy, 1992b) (Fig. 3). Sucrose dry wt.) Figure 3. Estimated western spruce budworm population growth (number of first instars alive at the beginning of the F,, F , and F, generations) for artificial diets with different levels of sucrose, assuming all populations were equal at the beginning of the Pi generation (redrawn from Clancy 1992b ). See Clancy (1991b) for model of population growth used to calculate the estimates The downward arrows (I) and corresponding italic numbers on the x-axis indicate the lowest and highest concentration of sugars observed in current-year Douglas-fir foliage....

Genes Involved in Bacterial Differentiation and Nodule Development

Carbon supply to the bacteroids is a strict requirement for the effective functioning of nodules. Symbiotic nitrogen fixation (SNF) depends primarily on the import of sucrose in the nodule. Sucrose synthase (SucS), cleaving sucrose in UDP-Glc and free fructoses, was shown to be essential for C supply, and plays a role in regulating the C metabolism and N fixation in nodules. Analysis in pea and M. truncatula revealed expression of the SucS gene in infected cells of the fixation zone, as well as in the meristematic region, prefixing zone, inner cortex, and nodule vasculature (Hohnjec et al. 2003). Antisense SucS1 plants of M. truncatula and the pea mutant rug4 showed less SucS activity, impaired SNF, and premature senescence (Gordon et al. 1999 Baier et al. 2007). Decreased SucS activity in nodules of rug4 mutants lowered the contents of soluble proteins in nodules and of the leghemoglobin, but did not influence the expression of nitrogenase genes. However, nitrogenase activity was...

Engineering Soluble Sugars

For several crop species, soluble sugar content is much more important than that of starch. This is either because soluble sugars such as sucrose are major reserve carbohydrates (e.g. in sugar cane and sugar beet), or, as in fruit-bearing species, because sugar is an important component of taste. An increase in sugar content in strawberry has been achieved through fruit-specific antisense repression of AGPase. Transgenic strawberry fruits showed a decrease in starch content of approximately 50 and an increase in total soluble solids of up to 37 (Park et al., 2006). In general, relatively little is known at the biochemical or genetic level about the factors that control the rate of sucrose storage in sugar beet taproots or sugar cane nodes. This reflects the intractability of both crops using genetics and the difficulties in assessing storage metabolism at the biochemical level. Factors controlling sucrose accumulation in storage tissues are photoassimilate partitioning on the whole...

Proteomics Of Developing Seeds

Seeds of legume species are an important protein source, with 20 to as much as 40 protein content. However, the fact that the major proteins stored in these seeds are poor in sulfur-containing amino acids and the presence of nutritionally undesirable compounds, such as protease inhibitors, remain limiting factors. To address these questions, seed development in M. truncatula was investigated at specific stages of seed filling 2 . One hundred twenty proteins differing in kinetics of appearance were subjected to MALDI-TOF-MS. These analyses allowed us to identify 84 of them, some of which had previously been shown to accumulate during seed development in legumes (e.g., legumins, vicilins, convicilins, and lipoxygenases), confirming the validity of M. truncatula as a model for analysis of legume seed filling. The study also revealed proteins presumably involved in cell division during embryogenesis (tubulin and annexin). Their abundance decreased before the accumulation of the major...

Early and Late Pollen Expressed Genes

Within a gene family was monitored at the microspore (MS), bicellular (BC), tricellular (TC) and mature pollen (MP) stages. Each gene is identified by the given name when available or by the AGI number. Underlined gene name indicates those that are specifically or preferentially expressed in pollen. Black line highlights genes that have been genetically or functionally characterized. A VIC K+ channel B VIC Cyclic Nucleotide-Gated ion Channel (CNGC) C GPH Sucrose-proton symporter sucrose transporter (SUC), TC 2.A.2 D Plasma membrane P3A-type H+-ATPase, TC 3.A.3 E Calmodulin-regulated Ca2+-transporting P2B-type ATPase, TC 3.A.3 F Cu2+-transporting and Zn2+ Co2+ Cd2+ Pb2+-transporting P1B-type ATPase, TC 3.A.3

Metabolic Control of Seed Storage Protein Synthesis 561 Nitrogen Availability and Signalling

Fig. 5.4 Schematic overview of assimilate uptake and primary storage pathway in maturing legume seeds. Potential targets for the manipulation of metabolic pathways are highlighted by circles. Sucrose and amino acids are taken up by transporters for sucrose and amino acids (SUT, AAP). Phosphoenolcaboxylase (PEPC) supply organic acids for amino acid biosynthesis. ADP-glucose pyrophosphorylase (AGP) is a key enzyme of starch production and plastidic glucose-6-P translocator (GPT) import carbon into heterotrophic plastids. Sucrose-non-fermenting-kinase (SnRKl) and abscisic acid (ABA) are involved in the mobilization of sucrose and other aspects of seed maturation (see text for details) Sucrose Sucrose Fig. 5.4 Schematic overview of assimilate uptake and primary storage pathway in maturing legume seeds. Potential targets for the manipulation of metabolic pathways are highlighted by circles. Sucrose and amino acids are taken up by transporters for sucrose and amino acids (SUT, AAP)....

TC Genes and the Transport Function

The number of maize endosperm-specific genes has been estimated as 5500 (Lai et al. 2004), 78 of them showing clear orthologs in the rice genome. The only large-scale analysis of tissue specificity available was carried out in wheat (Drea et al. 2005) using in situ hybridization analyses 3, 6, and 9 days after anthesis (DAA) kernel sections. In this study 76 out of 665 genes examined (expression data can be viewed at were found to be expressed in the modified aleurone, and among them 32 were found to be expressed exclusively in this tissue within the kernel. The function of the majority of these genes is currently unknown and, more surprisingly, the list does not contain genes involved in transport processes. A similar result has been found in the screening efforts conducted to identify TC-specific genes in barley and maize (see below). This indicates that the morphology and transport adaptation of TC is, very likely, not determined by the expression of tissue-specific genes but by...

Products of C4 metabolism can be identified by mass spectrometry

Measuring the distribution of the 12C and the 13C isotopes in a photosyn-thetic product (e.g., sucrose) can reveal whether it has been formed by C3 or C4 metabolism. 12C and 13C occur as natural carbon isotopes in atmospheric CO2 in the ratio of 98.89 and 1.11 , respectively. Due to a kinetic isotope effect RubisCO reacts with 12CO2 more rapidly than with 13CO2. For this reason, the ratio 13C 12C is lower in the products of C3 photosynthesis than in the atmosphere. The ratio 13C 12C can be determined by mass spectrometry and is expressed as a 613C value. As a standard, one uses the distribution of the two isotopes in a defined limestone. Products of C3 photosynthesis show 613C values of 28 V. In the PEP carboxylase reaction of C4 metabolism the preference for 12C over 13C is less pronounced. As in C4 plants practically the total amount of CO2 which is prefixed by PEP carboxylase reacts further in the bundle sheath cells with RubisCO, the photosynthesis of C4 plants yields a 613C value...

CO2 fixed during the night is stored as malic acid

Nocturnal fixation of CO2 is catalyzed by phosphoenolpyruvate carboxylase, in the same way as in the metabolism of C4 plants and guard cells (Fig. 8.4). In many CAM plants the phosphoenolpyruvate required is generated from the degradation of starch, but in other plants soluble carbohydrates, such as sucrose (section 9.2) and fructanes (section 9.5), may also serve as carbon stores. Figure 8.17 shows a scheme of the CAM metabolism using starch as a carbon reservoir. The starch located in the chloroplasts is degraded to triose phosphate (section 9.1), which is then exported via the triose

Polysaccharides are storage and transport forms of carbohydrates produced by photosynthesis

The various plant parts are supplied with carbohydrates via the sieve tubes (Chapter 13). A major transport form is the disaccharide sucrose, but in some plants also tri- and tetrasaccharides or sugar alcohols. Since the synthesis of carbohydrates by photosynthesis occurs only during the day, these carbohydrates have to be stored in the leaves to ensure their continued supply to the rest of the plant during the night or during unfavorable weather conditions. Moreover, plants need to build up carbohydrate stores to tide them over the winter or dry periods, and as a reserve in seeds for the initial phase of germination. For this purpose, carbohydrates are stored primarily in high molecular weight polysaccharides, in particular as starch or fructans, but also as low molecular weight oligosaccharides. Figure 9.1 Triose phosphate, the product of photosynthetic CO2 fixation, is either converted in the chloroplasts to starch or, after transport out of the chloroplasts, transformed to sucrose...

The Dimer of Dimers Structure

An interesting aspect of the presence of the two EPR signals associated with the S2 state is the series of conditions that have been shown to affect the relative intensities of the two signals. High concentrations (5 by volume) of small alcohols lead to complete elimination of the g 4.1 signal and an increase in the intensity of the multiline signal 41 . In contrast, high concentrations of sucrose, the presence of F-, Sr2+. or near infrared illumination, lead to an increase in the g 4.1 signal 35, 36, 42 . While no specific explanation of these results has been provided, they do suggest that the exchange couplings between the Mn ions in the cluster are extremely sensitive to a variety of conditions.

Food Plants Containing Fructans

Degree of polymerization can have a pronounced impact on the potential use of the inulin and fructooligosaccharides. Short-chain fructooligosaccharides (i.e., GF5) are of interest because of their health benefits, sweetness ( 30 of sucrose), and as a substrate for the synthesis of certain chemicals (e.g., fermentation products). Inulins with higher degrees of polymerization can be used for fat replacement and high-fructose syrups (longer chain lengths decrease the percentage of glucose in the syrup). Likewise, longer chain lengths can be systematically reduced in size by partial hydrolysis using an endo-inulinase, while lengthening is not a commercially viable option.

Early events in legume nodule formation

Colonization of legume roots by Rhizobium starts when the bacteria move chemotactically to the roots and there compounds present in the root exudate stimulate bacterial growth. Legume roots secrete flavonoids, such as luteolin and naringenin (Charrier et al. 1995, Shirley 1996, Bladergroen and Spaink 1998), that serve as chemoattractant to rhizobia (Caetano-Anolles et al. 1988). This is interesting as these compounds also activate a set of rhizobial genes that are involved in the synthesis of a compound molecule that sets in motion the process of root nodule formation (Zuanazzi et al. 1998). This set of rhizobial genes is named nodulation (nod) genes and the secreted signal molecule is the so-called Nod factor. Rhizobia produce Nod factors with a similar basic structure. This basic structure is made up of a backbone of three to five p 1,4-linked N-acetyl-D-glucosamine residues and a fatty acyl chain attached to the non-reducing sugar residue. Based on their structure Nod factors are...

Under Heterotrophic Or Photomixotrophic Condition

In conventional micropropagation including heterotrophic and photomixotrophic culture methods, the amount of CO2 uptake or net photosynthetic rate of plants in vitro is lower than plants in greenhouse or field controls (Donnelly and Vidaver, 1984). The net photosynthesis rate of birch plants regenerated in vitro was only one-third of those grown in the greenhouse, indicating the lack of full development of photosynthetic competency of plants in vitro (Smith et al., 1986). The low net photosynthetic rate of plants in vitro is attributed to the low RuBPcase activity (Grout, 1988), which was probably due to a high sucrose concentration in leaves of plants in vitro (Hdider and Desjardins, 1994). Development of new micropropagation systems for the control of in vitro environment is necessary to overcome the major shortcomings as described earlier for large-scale production of high quality plants in vitro. A great number of quality woody transplants can be produced at low cost with...

Terrestrial C4 plants subtypes biochemistry types of anatomy and photochemical requirements

Photosynthesis in C4 plants consists of the coordinated function of two cell types in the leaves, usually designated mesophyll cells (MC) and bundle sheath cells (BSC). In C4 plants, atmospheric C02 enters leaves through stomata and is first accessible to MC, where it is fixed by phosphoeno pyruvate (PEP) carboxylase to form oxaloacetate, and then malate and aspartate. These C4 dicarboxylic acids are transported to BSC, where they are decarboxylated, and C02 is concentrated and refixed by RuBP (ribulose bisphosphate) carboxylase and assimilated through the Calvin cycle to form sucrose and starch. Thus, in C4 plants, there is a spatial separation of C02 fixation into malate (occurring in MC) and use of C4 acids as donors of C02 to the C, pathway (occurring in BSC). Although anatomical differentiation is apparent in BSC, they are functionally similar in carbon assimilation to MC in C, plants, except for the presence of enzymes concerned with decarboxylation of C4 acids.

Necessity Of Photoautotrophic Micropropagation In Woody Transplant Production

Photoautotrophic micropropagation requires the growth of chlorophyllous explants on a sugar-free medium under pathogen-free and favorable in vitro environmental conditions, which enable plants in vitro to photosynthesize and produce their own carbohydrates for growth. A photoautotrophic micropropagation system with the improvement of in vitro aerial and root zone environments has significantly enhanced the growth of plants in vitro, increased the multiplication rate and thus, shortened the multiplication period of plants in vitro (Kozai et al., 1988). When plants in vitro are grown on sugar-free medium in a ventilated vessel under pathogen-free condition, loss of plants in vitro due to microbial contamination can be considerably reduced (microbes multiply rapidly only on the sugar-containing medium in most cases). On the other hand, by increasing light intensity and CO2 concentration inside the culture vessel during the photoperiod, the net photosynthetic rate of plants in vitro on...

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

As described in Chapter 13, the carbohydrates formed as the product of CO2 assimilation are transported from the leaves via the sieve tubes to various parts of the plants. The transport forms of the carbohydrates are sucrose, sugar alcohols (e.g., sorbitol), or raffinoses, depending on the species. There are no such special transport forms for the products of nitrate assimilation. All amino acids present in the mesophyll cells are exported via the sieve tubes. Therefore the sum of amino acids can be regarded as the final product of nitrate assimilation. Synthesis of these amino acids takes place mainly in the chloroplasts. The pattern of the amino acids synthesized varies largely, depending on the species and the metabolic conditions. In most cases glutamate and glutamine represent the major portion of the synthesized amino acids. Glutamate is exported from the chloroplasts in exchange for malate and glutamine in exchange with glutamate (Fig. 10.6). Also, serine and glycine, which are...

Microtubuleassociated proteins

(60, 62 and 68 kDa) of MAP65 bands on 1D SDS gels plus a couple of proteins less than 100 kDa. The isolated protein fraction stimulated sub-critical concentrations of tubulin to assemble into radiating arrays. Monospecific antibodies prepared against the three MAP65 bands stained all four MT arrays in carrot cells much as Jiang and Sonobe (1993) had found for tobacco. Later, Rutten etal. (1997) chro-matographically purified the 60 kDa band. This did not stimulate the assembly of tubulin at sub-critical concentrations, but it did stimulate assembly at concentrations of tubulin that would just self-assemble. It also stabilized brain MTs against the depolymerizing effects of cold and calcium. MAP60 did not bundle MTs. To separate the MAP65 proteins from the less than 100kDa proteins, Chan etal. (1999) separated the carrot MAP fraction by sucrose density gradient centrifuga-tion. The purified mixture of 60, 62 and 68 kDa proteins did not stimulate the assembly of tubulin but it did form...

Signalling and Positional Information in Protodermal Specification

The analysis of ALE1 has fuelled the ongoing debate regarding whether the correct specification and differentiation of the embryonic protoderm is dependent on signals from the surrounding endosperm. Interestingly, a parallel debate exists regarding the role of maternal tissues in the differentiation of the endosperm aleurone layer in cereals. As described previously, considerable evidence that outside or surface position is critical both for protoderm and for aleurone cell specification has been published. As a result it is natural that the finger should be pointed at surrounding tissues (the ESR for the protoderm, and the maternal nucellus for the aleurone) as a source of developmental signals. Indeed studies in maize have shown that several genes including small secreted peptides, including those encoding the secreted ESR-proteins (Opsahl-Ferstad et al. 1997 Bonello et al. 2000, 2002), are expressed in the embryo surrounding region of maize. ESR proteins belong to the CLE (CLV3 ESR)...

When will photosynthesis in C3 plants be C02Iimited

In general, photosynthesis in C, plants is limited mainly by light harvesting and assimilatory power under low light, and by carboxylation and photorespiration under limiting CO,. Under saturating-light and -CO, conditions, however, photosynthesis can be controlled by processes that convert triose-P into starch and sucrose (Sage 1990. 1994. Stitt 1986. 1996). Thus, the capacity to use triose-P for carbohydrate synthesis can establish an upper limit for the maximum rate of photosynthesis under CO,- and light-saturated conditions (Sage 1990. Sharkey et al 1995).

Synthesis Of Adpglucose In The Amyloplast

Either by the tissue carbohydrate status or by exogenous supply of carbon. In contrast, the expression of the large subunit is high in sink tissues and is enhanced by increased carbohydrate (sucrose) content (107, 108). The active enzyme requires polymerization between the large and small subunits. Studies of active reconstituted recombinant enzymes obtained from expression of potato AGPase genes in E. coli have established that the catalytic activity of the heterotetramer depends entirely on the small subunit given that the large subunit expressed alone did not show any AGPase activity (109, 110). Moreover, anti-sense repression of the small AGPase subunit in potato tubers results in less than 2 residual AGPase activity (23). Site-directed mutagenesis experiments on the GlclP binding site also confirmed that the role of the large subunit on catalysis is minimal (71). The main function of the large subunit appears to be the modulation of the activator (3-PGA) site via interaction with...

The nodule formation relies on a balanced interplay of bacterial and plant gene expression

Those proteins, which are required especially for the formation of nodules, and which are synthesized by the host plant in the course of nodule formation, are called nodulins. These nodulins include leghemoglobin (section 11.2), the enzymes of carbohydrate degradation (including sucrose synthase (section 9.2)), enzymes of the citrate cycle and the synthesis of glutamine and asparagines, and, if applicable, also of ureide synthesis. They also include an aquaporin of the peribacteroid membrane. Together, these proteins belong to the normal outfit of root cells, but are synthesized at elevated levels during nodule formation. The plant genes encoding these proteins are called nodulin genes. One differentiates between early and late nodulins. Early nodulins are involved in the process of infection and formation of nodules, and the expression of the corresponding genes is induced in part by signal compounds released from the rhizobia. Late nodulins are only synthesized after the formation...

Metabolic products are exchanged between bacteroids and host cells

The main substrate provided by the host cells to the bacteroids is malate (Fig. 11.4), synthesized from sucrose, which is delivered by the sieve tubes. Sucrose The sucrose is metabolized by sucrose synthase in the plant cell (Fig. 13.5), and further converted by glycolysis to phosphoenolpyruvate, which is subsequently carboxylated to oxaloacetate (see Fig. 10.11), and the latter is reduced to malate. Nodule cells contain high activities of phosphoenolpyruvate carboxylase. NH4 is delivered as a product of N2 fixation via a specific transporter to the host cell, where it is subsequently converted mainly into glutamine (Fig. 7.9) and asparagine (Fig. 10.14) and then transported via the xylem vessels to the other parts of the plant. It was recently shown that alanine can also be exported from bacteroids.

Photoautotrophic Micropropagation

It should be also noted that calli are not formed at the base of the shoot when grown on sugar-free medium with porous supporting materials, which is an advantage of woody plant micropropagation. Physiological mechanism of this phenomenon needs to be studied in the future.

Sugar Metabolism in AMF

AM fungi could cause changes in the regulation of plant genes in roots. Ravnsknov et al. (2003) demonstrated a higher gene expression of both Sus1 and Sh1, the two isoforms of sucrose synthase cleaving sucrose into hexoses, in maize roots colonized by different AM fungal isolates. Higher sucrose synthase gene expression was not related to the concentrations of sucrose, reducing sugars or starch in the root tissue whereas increasing soil phosphorus concentrations decreased this gene expression. The higher gene expression of gene coding for sucrose synthase in AM roots was measured during the earliest phase of root colonization by fungal isolates.

Leaf senescence in tissue culture of Passiflora incarnata L the role of ethylene

P. incarnata shoots were cultured on MS macro and microelements with Gamborg's B5 vitamins, reduced glutathione 300 mg L-1, MES 500 mg L-1, sucrose 20 g L-1, kinetin 2 mg L-1, agar 7 g L-1. Three different culture vessels were used Ury vials (PBI, Milan, Italy) 30 mL Red screw cap (PBI, Milan, Italy) disposable 200 mL vessels Magenta GA-7 (Sigma Chemical Co., St. Louis, USA). To elucidate the role of ethylene in leaf senescence ACC 10 M and AVG 10 M were added to the basal medium in Ury vials by microfiltration and SmartFreshSM (AgroFresh Inc. c o Rohm & Haas Italia srl) powder was used to provides the desired concentration of 1-MCP (500 ppm) in the internal headspace of the culture vessels. Chlorophyll a and b were detected spectrophotometrically on fresh leafy shoots at the end of the in vitro cultures. Ethylene was determined by gas chromatography.

Endosperm Cultures Derived from Central Cell Fertilization In Vitro and Embryo Sac Isolation Post Fertilization

Another approach to obtaining cultured endosperm cells, which avoids the technical hurdles associated with central cell fertilization in vitro, is through isolation and culture of the embryo sac shortly after fertilization in vivo. In maize this has been most recently accomplished through isolation of ovule sections containing the embryo sac 1 DAP and culture on a modified Murashige and Skoog (MS) medium containing 6-15 sucrose (Laurie et al. 1999). The authors used these cultures to generate viable embryos and mature plants without somatic embryogenesis, and describe the production of an endosperm from these embryo sacs in culture as well. However, similar to the technique described above, maternal tissue is included in the culture and it is indicated that the adjacent nucellar tissue may be supplying growth factors essential for stimulating development. Additionally, the remaining maternal tissue appears to continue to at least partially limit direct accessibility of the endosperm...

In Vitro Conservation of Germplasm

Protocols for in vitro conservation by slow growth of pepper and its related species viz., P. barberi, P. colubrinum, P. betle and P. longum were standardised (Geetha et al. 1995, Nirmal Babu et al. 1996b) by maintaining cultures at reduced temperatures, in the presence of osmotic inhibitors, at reduced nutrient levels and by minimising evaporation loss by using closed containers. Pepper cultures could be maintained in half strength WPM supplemented with 15 gl-1 each of sucrose and mannitol for one year with 85 per cent survival. In P. barberi full strength WPM with 25 gl-1 sucrose and 5 gl-1 mannitol was suitable for storage of cultures upto one year with 80 per cent survival. Shoot tips of P. longum and P. colubrinum could be stored upto one year in full strength WPM with 20 gl-1 sucrose and 10 gl-1 mannitol with 75 per cent and 70 per cent survival respectively. P. betle cultures could be stored in half strength WPM supplemented with 20 gl-1 sucrose for one year.

That Retains Cell and Organ Identity Without Maternal Tissue Presence

To further facilitate the study of cell and organ identity in in vitro grown maize endosperm in experiments aimed at identifying improved culture conditions, a transgenic maize line was developed in which aleurone cells are labeled with YFP as described above, starchy endosperm cells with cyan fluorescence protein (CFP) driven by the 27-kDa gamma zein promoter, and transfer cells with red fluorescent protein (RFP) driven by the END1 promoter (Gruis et al. 2006). When cultivating manually isolated 6-DAP embryo sacs from this marker line on a modified MS medium containing 15 w v sucrose (US Patent Pub. No. US 2006 0123518), the endosperm grew into a body of starchy endosperm cells that accumulated starch granules (Fig. 1b and c) covered by a single surface layer of YFP positive aleurone cells (Fig. 1d). The starchy endosperm fluoresced cyan from CFP driven by the 27-kDa y-zein promoter (Gruis et al. 2006). These observations, as well as others described below, confirm that the culture...

Regulatory consequences of intercellular metabolite transport

Several intermediates of the C4 and Benson-Calvin cycles act as effectors of enzyme activity. This has important consequences for the regulation of PEP carboxylase and of starch and sucrose synthesis, and perhaps other processes. For example, triose phosphates and hexose phosphates stimulate PEP carboxylase activity, whereas malate inhibits it (Gadal et al 1996). Consequences for carbohydrate synthesis. In maize, the synthesis of sucrose occurs in the mesophyll cells, although up to a third of the sucrose-phosphate synthase may occur in the bundle sheath of some C4 plants (Lunn and Furbank 1999), where one of its major functions may be sucrose synthesis following starch degradation at night. The ultimate substrate for sucrose synthesis, triose-P (and hence the amount of fructose-1,6-bisphosphate, FBP), is present in the mesophyll of C4 plants at far higher concentrations than in C, plants. The cytosolic fructose-1,6-bisphosphatase acts as a valve in...

Nodule Primary Metabolism

Root nodules are metabolically very active. The nodule is fed carbon sources, largely as sucrose, via the phloem this input is used as an energy source by the symbiont in N2 fixation and for the nodule for its own development. Moreover, the plant is thought to provide Frankia amino acids (Fig. 3) and must provide Frankia with nutrients. The nitrogen fixed and exported by Frankia is converted to plant available nitrogenous compounds in the nodule and transported to nitrogen sinks via the xylem. Because of the intricate relation between the two organisms, a complex integrated metabolic system is required for proper nodule development and function. Moreover, the nodule primary metabolism requires active and communicating pathways over the symbiotic interface.

Isolation of Nuclei and Protein Extraction

The nuclei were prepared from chickpea seedlings as described 20 . About 20 g of the tissue was ground into powder in liquid nitrogen with 0.3 (w w) PVPP and immediately transferred into an ice-cold 500-mL beaker containing 200 mL of ice-cold 1X HB (10 mM Trizma base, 80 mM KCl, 10 mM EDTA, 1 mM spermidine, 1 mM spermine, 0.5 M sucrose, pH 9.5) plus 0.15 2-ME and 0.5 Triton X-l00. The contents were gently stirred for 30 min for complete lysis of organeller membranes. This suspension was filtered through four layers of cheesecloth and two layers of Mira cloth into an ice-cold 250-mL centrifuge bottle. The homogenate was pelleted by centrifugation with a fixed-angle rotor at 1800g at 4 C for 20 min. The supernatant fluid was discarded and the pellet was gently resuspended in 30 mL of ice-cold wash buffer (1X HB minus Triton X-100). To remove the particulate matter remaining in the suspension, the resuspended nuclei were filtered into a 50-mL centrifuge tube through two layers of Mira...

Phloem transport distributes photoassimilates to the various sites of consumption and storage

The phloem is built from elongated cells, joined by sieve plates, the latter consisting of diagonal cell walls perforated by pores. The single cells are called sieve elements and their longitudinal arrangement is called the sieve tube (Fig. 13.2). The pores of the sieve plate are widened plasmodesmata lined with callose (section 9.6). The sieve elements can be regarded as living cells that have lost their nucleus, Golgi apparatus, and vacuoles, and contain only a few mitochondria, plastids, and some endoplasmic reticulum. The absence of many cellular structures specializes the sieve tubes for the longdistance transport of carbon- and nitrogen-containing metabolites and of various inorganic and organic compounds. In most plants sucrose is the main transport form for carbon, but some plants also transport oligosaccharides

Carbon Metabolism in Nodules

Nodules are strong sinks for carbon, as is evidenced by the fact that unin-fected cells in most types of actinorhizal nodules contain many plastids rich in starch grains (Newcomb and Wood 1987 Pawlowski 2002). The unloading of sucrose from the phloem in root nodules is followed by catabolism by either cytosolic sucrose synthase or by cytosolic, apoplastic or vacuolar in-vertase (van Ghelue et al. 1996 Lalonde et al. 2004). A part of the available carbon in nodules is converted to carbon compounds supplied to Frankia.

Involved In The Regulation Of Iron Deficiency Stress Responses By Strategy I Plants

Bienfait et al. (1987) found that either sterile potato roots grown on a sucrose medium or potato roots occurring on tubers without sprouts were able to develop some of the Fe deficiency stress responses (i.e. enhanced ferric reductase activity, acidification, root hairs and transfer cells) when grown in a Fe-free medium. These results clearly show that the root itself can control the development of Fe deficiency stress responses (Bienfait et al., 1987). Later on, working with sunflower plants consisting of an aerial part and two root systems (obtained by approach grafting), Romera et al.

The Tripartite Culture System

The presence of high sucrose and nutrient (N and P) contents in conventional tissue culture media - for example, 60 mmol NO3- in Murashige and Skoog (MS) medium (Murashige and Skoog 1962) vs 3.8 mmol in MSR (Declerck et al. 1998) - generally inhibits the germination of spores or the establishment of mycorrhizal roots in vitro (Schubert et al. 1987 Lubraco et al. 2000 Bressan 2002). The presence of 3 sucrose in the medium reduced hyphal growth compared to media with lower concentrations of sucrose (Becard and Fortin 1988). Bressan (2002) observed that high salt concentrations in the medium prevented mycorrhizal colonization ofsweet potato grown on different substrates (vermiculite, agar, hydroxyethyl cellulose). Media with a higher salt content and, in particular, with a higher N and P content, like MS medium and Hoagland solution (Hoagland and Arnon 1950), completely inhibited root colonization (Bressan 2002). Pons et al. (1983) found that the presence of sterilized soil was necessary...

Starch is deposited in plastids

In storage tissues, the delivered carbohydrates are mostly converted to starch and stored as such. In apoplastic phloem unloading, this may proceed by two alternative pathways. In the pathway colored red in Figure 13.5, the sucrose is taken up from the apoplast into the storage cells and converted there via sucrose synthase and UDP-glucose-pyrophosphory-lase to fructose and glucose 1-phosphate. In this reaction, pyrophosphate is consumed and UTP is generated. Phosphoglucomutase converts glucose 1-phosphate to glucose 6-phosphate. Alternatively, the enzyme invertase first hydrolyzes sucrose in the apoplast to glucose and fructose, and these two hexoses are then transported into the cell. This pathway is colored black in Figure 13.5. A fructokinase and a hexokinase (the latter phosphorylating mannose as well as glucose) catalyze the formation of the corresponding hexose phosphates. Glucose 6-phosphate is transported via the glucose 6-phosphate-phosphate translocator (see section 8.2) in...

Stem Reserves In Grain Filling

Schynder (1) also discusses the problems associated with designing experiments to accurately measure the stem contributions to accumulation of grain dry weight. Some of these problems can be illustrated by examining field data collected in the 1999 season. Wheat cv. Patterson was collected once or twice weekly from 9 days prior to anthesis through the conclusion of caryopsis weight gain. Ketose sugars (fructose, sucrose and fructan) accumulated and were remobilized from the stem twice during this period (Fig. 1). At first glance this data supports the remobilization of stored

Effects of UVB on macroalgae and seagrasses

Fluorescence emission spectra (excited at 620 nm) of the lowest fraction from a sucrose gradient obtained after solubilisation of cytoplasm from the cyanobacterium Anabaena sp. before and after increasing exposure times to artificial UV radiation from a transilluminator. (Modified from Sinha et al., 1995b). Fig. 5. Fluorescence emission spectra (excited at 620 nm) of the lowest fraction from a sucrose gradient obtained after solubilisation of cytoplasm from the cyanobacterium Anabaena sp. before and after increasing exposure times to artificial UV radiation from a transilluminator. (Modified from Sinha et al., 1995b).

Methodology And Strategy

Sucrose gradient Sucrose gradient Sucrose gradient Sucrose gradient Sucrose gradient - ultracentrifugation compartment or a systematic fractionation of the organelle. For instance, envelope membranes and plastoglobules were purified using sucrose density centrifugation 10, 11, 15, 16 . Stromal chloroplast fractions were purified by classical hypotonic lysis 9, 26 . Thylakoid membranes were purified by different wash treatments 7, 8 . Rupture of carefully washed thylakoids using a Yeda press was an easy and efficient method to isolate a highly pure fraction of soluble lumen proteins 2 . A similar approach using differently purified thylakoids yielded a fraction of peripheral thylakoid proteins that contained a higher amount of stroma proteins 3 .

Experimental Results And Applications

Chloroplasts have been in the focus of intense research for a long time, and the knowledge of their functions was already quite profound 20 years ago. The biochemical map of chloroplasts displayed in prominent positions the light reactions of photosynthesis, flanked by the Calvin cycle and the pathways for the synthesis of starch and sucrose. Photorespiration and the transport of metabolites across the envelope had been quite thoroughly studied, and much was known about the pathways for the biosynthesis of lipids, amino acids, chlorophylls, and carotenoids. In summary, chloroplasts were a well-studied biological system, when chloroplast proteomics started to develop. That leads to the question has proteomics contributed to our knowledge of the chloroplast

Golgi Associated Cell Wall Metabolism

A wide array of biological molecules including proteins, hormones, secondary metabolites, and lipids can be modified with sugar moieties that alter the structural conformation of the molecules. These sugars are attached by an armada of glyco-syltransferases that monitor structural and physiological requirements for sugar attachments (Lairson et al. 2008). The Arabidopsis genome contains more than 400 glycosyltransferases (http, and a large proportion of these are required to catalyze the 30 plus linkages observed in the cell wall matrix polysaccharides (Lairson et al. 2008). Many sugar transfer reactions are carried out in the Golgi apparatus where type II membrane glycosyltransferases utilize nucleotide-activated sugars as precursors to processively synthesize different carbohydrate linkages to form hemicellulosic and pectic polymers (Seifert 2004). One example of such type II GTs is the cellulose synthase (CESA) gene family (Richmond 2000 Fig. 3), part of the cellulose...

Non Essential Element Uptake and Translocation by AM Fungi

A bi-compartment monoxenic culture system allowing the spatial separation of a central root compartment (RC) for the growth of mycorrhizal roots from a neighbouring external hyphal compartment (HC) where extraradical mycelia and or roots were allowed to grow (a). The synthetic growth medium was solid in the RC, while the HC contained a liquid growth medium lacking sucrose and vitamins. Numerous hyphae crossed the partition between the RC and HC. Once in contact with the liquid growth medium, an abundant branched mycelium developed, and thousands of spores were produced. Magnified view of hyphae and spores in the HC b Fig. 1a, b. A bi-compartment monoxenic culture system allowing the spatial separation of a central root compartment (RC) for the growth of mycorrhizal roots from a neighbouring external hyphal compartment (HC) where extraradical mycelia and or roots were allowed to grow (a). The synthetic growth medium was solid in the RC, while the HC contained a liquid...

Mass Balance And Pulse Chase Experiments

Sucrose is the substrate for fructan synthesis in stem storage tissues. Sucrose transported in the phloem may be unloaded from the phloem symplastically or apoplastically in the internode tissues (56). The difference between these pathways is in the free space hydrolysis of sucrose by invertase (57). It is possible that an invertase inhibitor could be active in the apoplast (57) so sucrose could travel via the free space to the storage cells without hydrolysis. Sink specific expression of the sucrose symporter genes SUT1 SUT2 has been reported for other plant species so sucrose could be the species arriving at the site of fructan synthesis in stem tissues (58). However in the axial pathway phloem unloading is probably symplastic controlled by diffusion gradients dependent on a low cytoplasmic sucrose concentration because of fructan synthesis in the vacuole (56). Because all the sugars in the pathway are osmotically active bulk flow in response to turgor pressure differences in...

Nitrate transporters and white photosynthetic active light

Photosynthesis and carbon metabolism were recognised as important for nitrogen assimilation already in the early days of research on nitrogen assimilation back in the 50's using unicellular algae as the experimental system as reviewed by Huppe and Turpin (1994). An early observation was that nitrogen-sufficient algae required light to assimilate nitrogen, but nitrogen-limited cells rapidly assimilated nitrogen in the dark. Intracellular carbohydrate stores decreased during dark assimilation and assimilation ceased when these stores were depleted (Huppe and Turpin 1994). From experiments on photosynthesis and uptake of 15NO3- in maize seedlings, Pace et al. (1990) concluded that NO3- uptake and reduction were regulated by the supply of energy and carbon skeletons required to support these processes. Also in ryegrass NO3- uptake was closely related to photosynthesis with a time lag of about 5 h between photosynthesis and uptake (Scaife 1989). Furthermore diurnal regulation of nitrate...

Integration of Chloroplast Metabolism with Host Metabolism Was a Host Driven Process

As outlined already, one of the major chloroplast envelope transporter families (i.e., the pPTs) has evolved from sugar NTTs of the host endomembrane system. Naturally, this discovery prompted the question about the evolutionary origin of chloroplast transporters in extant photosynthetic eukaryotes. Comprehensive phylogenomic and phylogenetic analysis of plastid envelope-localized transporters of Arabidopsis thaliana showed that at least 50 of the envelope permeome evolved from preexisting host proteins, whereas only a small portion was contributed by the endosymbiont (Tyra et al. 2007). That is, integration of plastid and host metabolism was predominantly a host-driven process. Transport proteins encoded by the host genome acquired targeting signals for routing to the chloroplast and were inserted into the chloroplast envelope membrane. A surprisingly large share of plastid envelope membrane transporters, such as the adenine NTTs, the dicarboxylate translocators (DiTs), and some...

Laboratory and greenhouse

We have focused on in situ studies in this review, but some results of studies performed in laboratories and greenhouses are listed briefly below as well. Short-term UV-enhancement studies have lasted from six days to three months. The aquatic moss Fontinalis antipyretica showed a decrease in photosynthetic pigments, photosynthesis, and growth, and an increase in dark respiration rate and schlerophylly, with shade samples being more sensitive (Martinez-Abaigar et al. 2003 Numez-Olivera et al. 2004,2005). In Hylocomium splendens, phenological development was accelerated and growth increased (Johanson et al. 1995). Leucobryum glaucum, Mnium hornum, Plagiomnium undulatum, and Plagiothecium undulatum showed decreases in fluorescence (Takacs et al. 1999 Csintalan et al. 2001). In Polytrichum commune, a 15 ozone depletion decreased photosynthetic pigments and UV-absorbing compounds, and increased sucrose and glucose synthesis, but a 25 ozone depletion induced an increase in photosynthetic...

Carbon Distribution and Transfer to the Fungus

Fig. 1 Carbon assimilation, distribution and metabolism. The graphs show the way of carbon from the athmosphere through a mycorrizal plant and the AM fungus to the soil. Question marks indicate steps where significant gaps in the knowledge about the molecular-physiological background exist carbohydrate metabolism from assimilation to sucrose, distribution of sucrose in the plant, the way of carbon transfer from the plant to the fungus, the final branches of carbohydrate metabolism and distribution in the extraradical mycelium Fig. 1 Carbon assimilation, distribution and metabolism. The graphs show the way of carbon from the athmosphere through a mycorrizal plant and the AM fungus to the soil. Question marks indicate steps where significant gaps in the knowledge about the molecular-physiological background exist carbohydrate metabolism from assimilation to sucrose, distribution of sucrose in the plant, the way of carbon transfer from the plant to the fungus, the final branches of...

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