Role of glutathione in adaptation and signalling during chilling and cold acclimation in plants

Glutathione and glutathione reductase: a boon in disguise for plant abiotic stress defense operations

Abiotic stresses such as salinity, drought, clilling, heavy metal are the major limiting factors for crop productivity. These stresses induce the overproduction of reactive oxygen species (ROS) which are highly reactive and toxic, which must be minimized to protect the cell from oxidative damage. The cell organelles, particularly chloroplast and mitochondria are the major sites of ROS production in plants where excessive rate of electron flow takes place. Plant cells are well equipped to efficiently scavenge ROS and its reaction products by the coordinated and concerted action of antioxidant machinery constituted by vital enzymatic and non-enzymatic antioxidant components. Glutathione reductase (GR, EC 1.6.4.2) and tripeptide glutathione (GSH, γ-Glutamyl-Cysteinyl-Glycine) are two major components of ascorbate-glutathione (AsA-GSH) pathway which play significant role in protecting cells against ROS and its reaction products-accrued potential anomalies. Both GR and GSH are physiologically linked together where, GR is a NAD(P)H-dependent enzymatic antioxidant and efficiently maintains the reduced pool of GSH - a cellular thiol. The differential modulation of both GR and GSH in plants has been widely implicated for the significance of these two enigmatic antioxidants as major components of plant defense operations. Considering recent informations gained through molecular-genetic studies, the current paper presents an overview of the structure, localization, biosynthesis (for GSH only), discusses GSH and GR significance in abiotic stress (such as salinity, drought, clilling, heavy metal)-exposed crop plants and also points out unexplored aspects in the current context for future studies.

Label-free quantitative proteomics analysis of dormant terminal buds of poplar

Induction and break of bud dormancy are important features for perennial plants surviving extreme seasonal variations in climate. However, the molecular mechanism of the dormancy regulation, still remain poorly understood. To better understand the molecular basis of poplar bud dormancy, we used a label-free quantitative proteomics method based on nanoscale ultra performance liquid chromatography-ESI-MS(E) for investigation of differential protein expression during dormancy induction, dormancy, and dormancy break in apical buds of poplar (Populus simonii × P. nigra). Among these identified over 300 proteins during poplar bud dormancy, there are 74 significantly altered proteins, most of which involved in carbohydrate metabolism (22 %), redox regulation (19 %), amino acid transport and metabolism (10 %), and stress response (8 %). Thirty-one of these proteins were up-regulated, five were down-regulated during three phase, and thirty-eight were expressed specifically under different conditions. Pathway analysis suggests that there are still the presence of various physiological activities and a particular influence on photosynthesis and energy metabolism during poplar bud dormancy. Differential expression patterns were identified for key enzymes involved in major metabolic pathways such as glycolysis and the pentose phosphate pathway, thus manifesting the interplay of intricate molecular events in energy generation for new protein synthesis in the dormant buds. Furthermore, there are significant changes present in redox regulation and defense response proteins, for instance in peroxidase and ascorbate peroxidase. Overall, this study provides a better understanding of the possible regulation mechanisms during poplar bud dormancy.

Proteomic changes associated with freeze-thaw injury and post-thaw recovery in onion (Allium cepa L.) scales

The ability of plants to recover from freeze-thaw injury is a critical component of freeze-thaw stress tolerance. To investigate the molecular basis of freeze-thaw recovery, here we compared the proteomes of onion scales from unfrozen control (UFC), freeze-thaw injured (INJ), and post-thaw recovered (REC) treatments. Injury-related proteins (IRPs) and recovery-related proteins (RRPs) were differentiated according to their accumulation patterns. Many IRPs decreased right after thaw without any significant re-accumulation during post-thaw recovery, while others were exclusively induced in INJ tissues. Most IRPs are antioxidants, stress proteins, molecular chaperones, those induced by physical injury or proteins involved in energy metabolism. Taken together, these observations suggest that while freeze-thaw compromises the constitutive stress protection and energy supply in onion scales, it might also recruit 'first-responders' (IRPs that were induced) to mitigate such injury. RRPs, on the other hand, are involved in the injury-repair program during post-thaw environment conducive for recovery. Some RRPs were restored in REC tissues after their first reduction right after thaw, while others exhibit higher abundance than their 'constitutive' levels. RRPs might facilitate new cellular homeostasis, potentially by re-establishing ion homeostasis and proteostasis, cell-wall remodelling, reactive oxygen species (ROS) scavenging, defence against possible post-thaw infection, and regulating the energy budget to sustain these processes.

Efficiency of yeast in enhancement of the oxidative defense system in salt-stressed flax seedlings

The combined effects of yeast (1 ppm) and salinity on germination, seedling growth, metabolite accumulation and antioxidant defense system of flax (Linum usitatissimum) seeds grown at 100, 200 and 300 mM NaCl were studied. In this investigation, the germination was completely inhibited at 300 mM NaCl. Moreover, salinity induced marked increases in lipid peroxidation product (MDA), soluble carbohydrates as well as the reduced glutathione which were concomitant with sharp decrease in total phenols and ascorbic acid contents in 12-day-old flax seedlings. Furthermore, NaCl treatments increased the activities of some antioxidant enzymes (superoxide dismutase; SOD, peroxidase; POX and polyphenol oxidase; PPO). On the other hand, yeast treatments under salinity stress restored the membrane integrity and improved seedling growth. The results suggested that yeast treatments mitigated salinity stress via accumulation of some osmoprotectants such as free amino acids particularly proline which associated with elevating the defense system in terms of ascorbic acid, glutathione and total phenol contents. Yeast treatments also stimulated the activities of some antioxidant enzymes, preventing membrane peroxidation resulting in high capacity for germination and improved seedling growth under sever salt stress.

Hydrogen peroxide is involved in the cold acclimation-induced chilling tolerance of tomato plants

Cold acclimation increases plant tolerance to a more-severe chilling and in this process an accumulation of H(2)O(2) in plants is often observed. To examine the role of H(2)O(2) in cold acclimation in plants, the accumulation of H(2)O(2), antioxidant metabolism, the glutathione redox state, gas exchange and chlorophyll fluorescence were analyzed after cold acclimation at 12/10 °C and during the subsequent chilling at 7/4 °C in tomato (Solanum lycopersicum) plants. Cold acclimation modestly elevated the levels of H(2)O(2), the gene expression of respiratory burst oxidase homolog 1 (Rboh1) and NADPH oxidase activity, leading to the up-regulation of the expression and activity of antioxidant enzymes. In non-acclimated plants chilling caused a continuous rise in the H(2)O(2) content, an increase in the malondialdehyde (MDA) content and in the oxidized redox state of glutathione, followed by reductions in the CO(2) assimilation rate and the maximum quantum yield of photosystem II (F(v)/F(m)). However, in cold-acclimated plants chilling-induced photoinhibition, membrane peroxidation and reductions in the CO(2) assimilation rate were significantly alleviated. Furthermore, a treatment with an NADPH oxidase inhibitor or H(2)O(2) scavenger before the plants subjected to the cold acclimation abolished the cold acclimation-induced beneficial effects on photosynthesis and antioxidant metabolism, leading to a loss of the cold acclimation-induced tolerance against chilling. These results strongly suggest that the H(2)O(2) generated by NADPH oxidase in the apoplast of plant cells plays a crucial role in cold acclimation-induced chilling tolerance.

Glutathione improves the cold resistance of Lactobacillus sanfranciscensis by physiological regulation

The microenvironmental manipulation of glutathione (GSH) on improving cold resistance of Lactobacillus sanfranciscensis DSM 20451(T) was investigated in this study. It was proved that GSH relieves the metabolic disorder of cells under cold stress, and prevents the decreased activities of related key enzymes such as pyruvate kinase (PK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase (LDH) upon cold challenges. Higher intracellular ATP level was also found in cells with GSH under cold stress. Moreover, cells with imported GSH had significantly higher intracellular than the control during cold treatment. In addition, proteomics analysis showed more exciting findings that the protective function of GSH under cold stress was related to metabolic regulation and the multi-control against induced cross-stresses. These results broaden the knowledge about the physiological function of GSH, and suggest a practicable approach to improve the cold resistance of L. sanfranciscensis, a starter culture for sourdough, by the addition of GSH.

Metabolic dynamics during autumn cold acclimation within and among populations of Sitka spruce (Picea sitchensis)

• Autumnal cold acclimation in conifers is a complex process, the timing and extent of which vary widely along latitudinal gradients for many tree species and reflect local adaptation to climate. Although previous studies have detailed some aspects of the metabolic remodelling that accompanies cold acclimation in conifers, little is known about global metabolic dynamics, or how these changes vary among phenotypically divergent populations. • Using untargeted GC-MS metabolite profiling, we monitored metabolic dynamics during autumnal cold acclimation in three populations of Sitka spruce from the southern, central, and northern portions of the species range, which differ in both the timing and extent of cold acclimation. • Latitudinal variation was evident in the nature, intensity, and timing of metabolic events. Early development of strong freezing tolerance in the northern population was associated with a transient accumulation of amino acids. By late autumn, metabolic profiles were highly similar between the northern and central populations, whereas profiles for the southern population were relatively distinct. • Our results provide insight into the metabolic architecture of latitudinal adaptive variation in autumn acclimation and show that different mechanisms are the basis of early October cold hardiness and autumn-acclimated cold hardiness.

Metabolism of reactive oxygen species and reactive nitrogen species in pepper (Capsicum annuum L.) plants under low temperature stress

Low temperature is an environmental stress that affects crop production and quality and regulates the expression of many genes, and the level of a number of proteins and metabolites. Using leaves from pepper (Capsicum annum L.) plants exposed to low temperature (8 °C) for different time periods (1 to 3 d), several key components of the metabolism of reactive nitrogen and oxygen species (RNS and ROS, respectively) were analysed. After 24 h of exposure at 8 °C, pepper plants exhibited visible symptoms characterized by flaccidity of stems and leaves. This was accompanied by significant changes in the metabolism of RNS and ROS with an increase of both protein tyrosine nitration (NO(2) -Tyr) and lipid peroxidation, indicating that low temperature induces nitrosative and oxidative stress. During the second and third days at low temperature, pepper plants underwent cold acclimation by adjusting their antioxidant metabolism and reverting the observed nitrosative and oxidative stress. In this process, the levels of the soluble non-enzymatic antioxidants ascorbate and glutathione, and the activity of the main NADPH-generating dehydrogenases were significantly induced. This suggests that ascorbate, glutathione and the NADPH-generating dehydrogenases have a role in the process of cold acclimation through their effect on the redox state of the cell.

The significance of glutathione for photoprotection at contrasting temperatures in the alpine plant species Soldanella alpina and Ranunculus glacialis

The significance of total glutathione content was investigated in two alpine plant species with highly differing antioxidative scavenging capacity. Leaves of Soldanella alpina and Ranunculus glacialis incubated for 48 h in the presence of buthionine-sulfoximine had 50% lower glutathione contents when compared with leaves incubated in water. The low leaf glutathione content was not compensated for by activation of other components involved in antioxidative protection or electron consumption. However, leaves with normal but not with low glutathione content increased their ascorbate content during high light (HL) treatment (S. alpina) or catalase activity at low temperature (LT) (R. glacialis), suggesting that the mere decline of the leaf glutathione content does not act as a signal to ameliorate antioxidative protection by alternative mechanisms. CO(2)-saturated oxygen evolution was not affected in glutathione-depleted leaves at various temperatures, except at 35°C, thereby increasing the high temperature (HT) sensitivity of both alpine species. Leaves with low and normal glutathione content were similarly resistant to photoinhibition and photodamage during HL treatment at ambient temperature in the presence and absence of paraquat or at LT. However, HL- and HT-induced photoinhibition increased in leaves with low compared to leaves with normal glutathione content, mainly because the recovery after heat inactivation was retarded in glutathione-depleted leaves. Differences in the response of photosystem II (PSII) activity and CO(2)-saturated photosynthesis suggest that PSII is not the primary target during HL inactivation at HT. The results are discussed with respect to the role of antioxidative protection as a safety valve for temperature extremes to which plants are not acclimated.

Transgenic potato overproducing L-ascorbic acid resisted an increase in methylglyoxal under salinity stress via maintaining higher reduced glutathione level and glyoxalase enzyme activity

Salt-tolerance was studied in transgenic potato. It was conferred by overexpression of ascorbate pathway enzyme (D-galacturonic acid reductase, GalUR). As genetic engineering of the GalUR gene in potato enhances its ascorbic acid content (L-AsA), and subsequently plants suffered minimal oxidative stress-induced damage, we now report on the comprehensive aptness of this engineering approach for enhanced salt tolerance in transgenic potato (Solanum tuberosum L. cv. Taedong Valley). Potatoes overexpressing GalUR grew and tuberized in continuous presence of 200 mM of NaCl. The transgenic plants maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio together with enhanced activity of glutathione dependent antioxidative and glyoxalase enzymes under salinity stress. The transgenics resisted an increase in methylglyoxal that increased radically in untransformed control plants under salinity stress. This is the first report of genetic engineering of ascorbate pathway gene in maintaining higher level of GSH homeostasis along with higher glyoxalase activity inhibiting the accumulation in methylglyoxal (a potent cytotoxic compound) under salt stress. These results suggested the engineering of ascorbate pathway enzymes as a major step towards developing salinity tolerant crop plants.

Low temperature and oxidative stress in cereals

Low temperature stress results in significant yield losses in cereals. Cereals of subtropical origin like maize and rice are severely damaged at temperatures below 10°C and are killed at subzero temperatures. This stress effect is called chilling. In contrast, cereals originating from the temperate zone (wheat, barley, rye and oat) may survive short periods even between −10 and −20°C, depending on the species and varieties, so they are freezing-tolerant to various extents. For the winter type of these cereals a gradual decrease in temperature up to −4°C results in cold acclimation, which increases their freezing tolerance. In addition, it fulfils their vernalization requirement, which is necessary for the correct timing of the vegetative to generative transition. During both chilling and freezing, oxidative stress is induced. Although the accumulation of high concentrations of reactive oxygen species may be lethal, a moderate increase in their level may activate various defence mechanisms. In this review the role of reactive oxygen species, antioxidants, carbohydrates, free amino acids, polyamines and hormones in the response to low temperature stress in cereals will be described. The effect of light and the use of the model plant Brachypodium distachyon L. to reveal the biochemical and molecular biological background of this response will also be discussed.

The Arabidopsis LSD1 gene plays an important role in the regulation of low temperature-dependent cell death

In higher plants, the crosstalk between cold stress responses and reactive oxygen species (ROS) signaling is not well understood. *Two chilling-sensitive mutants, chs4-1 and chs4-3, were characterized genetically and molecularly. *The CHS4 gene, identified by map-based cloning, was found to be identical to lesion simulating disease resistance 1 (LSD1). We therefore renamed these two alleles lsd1-3 and lsd1-4, respectively. These two mutants exhibited an extensive cell death phenotype under cold stress conditions. Consistently, lsd1-3 plants exposed to cold showed up-regulation of the PR1 and PR2 genes, and increased accumulation of salicylic acid. These results indicate that low temperature is another trigger of cell death in lsd1 mutants. Furthermore, lsd1-3 plants accumulated higher concentrations of H(2)O(2) and total glutathione under cold conditions than wild-type plants. Genetic analysis revealed that PAD4 and EDS1, two key signaling regulators mediating resistance responses, are required for the chilling-sensitive phenotype of lsd1-3. *These findings reveal a role of LSD1 in regulating cell death trigged by cold stress and a link between cold stress responses and ROS-associated signaling.

Responses of antioxidant systems after exposition to rare earths and their role in chilling stress in common duckweed (Lemna minor L.): a defensive weapon or a boomerang?

Extensive agriculture application of rare earth elements (REEs) in Far East countries might cause spreading of these metals in aquatic and terrestrial ecosystems, thus inducing a growing concern about their environmental impact. In this work the effects of a mix of different REE nitrate (RE) and of lanthanum nitrate (LA) on catalase and antioxidant systems involved in the ascorbate-glutathione cycle were investigated in common duckweed Lemna minor L. The results indicated that L. minor shows an overall good tolerance to the presence of REEs in the media. Treatments at concentrations up to 5 mM RE and 5 mM LA did not cause either visible symptoms on plants or significant effects on reactive oxygen species (ROS) production, chlorophyll content, and lipid peroxidation. Toxic effects were observed after 5 days of exposition to 10 mM RE and 10 mM LA. A remarkable increase in glutathione content as well as in enzymatic antioxidants was observed before the appearance of the stress symptoms in treated plants. Duckweed plants pretreated with RE and LA were also exposed to chilling stress to verify whether antioxidants variations induced by RE and LA improve plant resistance to the chilling stress. In pretreated plants, a decrease in ascorbate and glutathione redox state and in chlorophyll content and an increase in lipid peroxidation and ROS production levels were observed. The use of antioxidant levels as a stress marker for monitoring REE toxicity in aquatic ecosystems by means of common duckweed is discussed.

Chilling stress and mitochondrial genome rearrangement in the MSC16 cucumber mutant affect the alternative oxidase and antioxidant defense system to a similar extent

The mosaic MSC16 cucumber (Cucumis sativus L.) mutant, which houses a rearranged mitochondrial genome, has altered respiratory chain activity, with a dysfunctional Complex I, increased external NADH dehydrogenases (ND(ex)) activity, and a higher alternative oxidase (AOX) capacity and AOX protein level. In the present study, changes in oxidative defense metabolism resulting from the respiratory chain dysfunction in the MSC16 mutant were compared with those induced by chilling. Chilling increased the enzymatic and non-enzymatic antioxidant defense systems in the wild-type (WT) but not in MSC16, which displays elevated antioxidant defenses as a result of the mitochondrial mutation. The high AOX capacity and protein level in MSC16 were unchanged as a result of chilling, whereas chilling increased these parameters in WT leaves. In mitochondria isolated from WT plants, superoxide was produced to a similar extent in the matrix and the intermembrane space, but in MSC16 mitochondria superoxide was produced largely within the intermembrane space. Mitochondria isolated from both genotypes after chilling showed increased superoxide production within the intermembrane space. Cytochemical detection revealed an increased abundance of H2O2 in the mitochondrial membrane in mesophyll cells of MSC16 leaves. The mitochondrial mutation also resulted in changes in the antioxidative defense system, including AOX, which were similar to those observed following chilling. The results presented here support the hypothesis that AOX is an effective marker of the cellular reprogramming resulting from stress. Moreover, we propose a role for reactive oxygen species (ROS) generated within the mitochondria in signal transduction.

Exogenous spermidine affects polyamine metabolism in salinity-stressed Cucumis sativus roots and enhances short-term salinity tolerance

We investigated the effects of short-term salinity stress and spermidine application to salinized nutrient solution on polyamine metabolism and various stress defense reactions in the roots of two cucumber (Cucumis sativus L.) cultivars, Changchun mici and Jinchun No. 2. Seedlings grown in nutrient solution salinized with 50mM NaCl for 8d displayed reduced relative water content, net photosynthetic rates and plant growth, together with increased lipid peroxidation and electrolyte leakage in the roots. These changes were more marked in cv. Jinchun No. 2 than in cv. Changchun mici, confirming that the latter cultivar is more salinity-tolerant than the former. Salinity stress caused an increase in superoxide and hydrogen peroxide production, particularly in cv. Jinchun No. 2 roots, while the salinity-induced increase in antioxidant enzyme activities and proline contents in the roots was much larger in cv. Changchun mici than in cv. Jinchun No. 2. In comparison to cv. Jinchun No. 2, cv. Changchun mici showed a marked increase in arginine decarboxylase, ornithine decarboxylase, S-adenosylmethionine decarboxylase and diamine oxidase activities, as well as free spermidine and spermine, soluble conjugated and insoluble bound putrescine, spermidine and spermine contents in the roots during exposure to salinity. On the other hand, spermidine application to salinized nutrient solution resulted in alleviation of the salinity-induced membrane damage in the roots and plant growth and photosynthesis inhibition, together with an increase in polyamine and proline contents and antioxidant enzyme activities in the roots of cv. Jinchun No. 2 but not of cv. Changchun mici. These results suggest that spermidine confers short-term salinity tolerance on cucumber probably through inducing antioxidant enzymes and osmoticants.

Stress hormones and abiotic stresses have different effects on antioxidants in maize lines with different sensitivity

The effect of stress hormones and abiotic stress treatments on reactive oxygen species and on antioxidants was compared in two maize (Zea mays L.) lines (Penjalinan and Z7) having different stress tolerance. Following treatment with abscisic acid, salicylic acid or hydrogen peroxide, the amount of hydrogen peroxide and lipid peroxides increased, while after osmotic stress or cultivation in continuous darkness, the levels were unchanged or decreased. The higher amount of lipid peroxides in Penjalinan indicated its greater sensitivity compared to Z7. The level of the examined antioxidants was increased by nearly all treatments. Glutathione and cysteine contents were higher after salicylic acid, hydrogen peroxide and polyethylene glycol treatments and lower after application of abscisic acid, NaCl and growth in darkness in Z7 than in Penjalinan. The activity of glutathione reductase, ascorbate peroxidase, catalase and glutathione S-transferase was higher after almost all treatments in Z7. The expression of the glutathione synthetase (EC 6.3.2.3) gene was not affected by the treatments, while the level of gamma-glutamylcysteine synthetase (EC 6.3.2.2) and glutathione reductase (EC 1.6.4.2) transcripts increased after most treatments. The two stress hormones and the stress treatments resulted in different changes in antioxidant levels in the two maize lines, which indicates the specific, stress tolerance-dependent response of plants to the various growth regulators and adverse environmental effects that were examined.

Cross tolerance to heavy-metal and cold-induced photoinhibiton in leaves of Pisum sativum acclimated to low temperature

Under high light intensity, low temperatures as well as heavy metals induce photoinhibition of PSII and oxidative stress in leaves. Since cold acclimation of leaves ameliorates their capacity of antioxidative defence, cross tolerance between cold-induced and heavy metal-induced photoinhibition was investigated in pea leaves grown at either 22 °C or 6 °C. The experimental conditions were chosen to induce a uniform level of short-term photoinhibition at low temperature or in the presence of CuSO4 or CdCl2 in leaves grown at 22 °C. Under all conditions photoinhibition of PSII was lower in cold-acclimated (6°C-grown) than in non-acclimated (22°C-grown) pea leaves. In darkness PSII was not affected by all treatments. Other parameters like catalase activity, chlorophyll content and metabolite contents were most sensitive to CuSO4, but less affected by CdCl2 and low temperature treatments. Strong oxidation of ascorbate and concomitant loss of catalase activity showed the enhanced oxidative stress in CuSO4-treated leaves. Generally, all measured parameters were less affected in cold-acclimated leaves than in non-acclimated leaves under all experimental conditions. Cold-acclimated pea leaves contained higher levels of ascorbate and particularly of glutathione and a higher capacity to keep the primary electron acceptor of PSII more oxidised. Incubation with heavy metals caused a nearly complete loss of reduced glutathione. It is suggested that reduced glutathione served as a source for phytochelatin synthesis. The extraordinarily high glutathione content in cold-acclimated pea leaves might therefore increase their ability to chelate heavy metals and thus to protect leaves from heavy-metal induced damage.

Multilevel genomic analysis of the response of transcripts, enzyme activities and metabolites in Arabidopsis rosettes to a progressive decrease of temperature in the non-freezing range

This paper characterizes the transcriptional and metabolic response of a chilling-tolerant species to an increasingly large decrease of the temperature. Arabidopsis Col-0 was grown at 20 degrees C and transferred to 17, 14, 12, 10 or 8 degrees C for 6 and 78 h, before harvesting the rosette and profiling >22 000 transcripts, >20 enzyme activities and >80 metabolites. Most parameters showed a qualitatively similar response across the entire temperature range, with the amplitude increasing as the temperature decreased. Transcripts typically showed large changes after 6 h, which were often damped by 78 h. Genes were induced for sucrose, proline, raffinose, tocopherol and polyamine synthesis, phenylpropanoid and flavonoid metabolism, fermentation, non-phosphorylating mitochondrial electron transport, RNA processing, and protein synthesis, targeting and folding. Genes were repressed for carbonic anhydrases, vacuolar invertase, and ethylene and jasmonic acid signalling. While some enzyme activities and metabolites changed rapidly, most changed slowly. After 6 h, there was an accumulation of phosphorylated intermediates, a shift of partitioning towards sucrose, and a perturbation of glycine decarboxylation and nitrogen metabolism. By 78 h, there was an increase of the overall protein content and many enzyme activities, a general increase of carbohydrates, organic and amino acids, and an increase of many stress-responsive metabolites including raffinose, proline, tocopherol and polyamines. When the responses of transcripts and metabolism were compared, there was little agreement after 6 h, but considerable agreement after 78 h. Comparison with the published studies indicated that much, but not all, of the response was orchestrated by the CBF programme. Overall, our results showed that transcription and metabolism responded in a continuous manner across a wide range of temperatures. The general increase of enzyme activities and metabolites emphasized the positive and compensatory nature of this response.

Factors contributing to enhanced freezing tolerance in wheat during frost hardening in the light

The interaction between light and temperature during the development of freezing tolerance was studied in winter wheat (Triticum aestivum L. var. Mv Emese). Ten-day-old plants were cold hardened at 5 degrees C for 12 days under normal (250 micromol m(-2)s(-1)) or low light (20 micromol m(-2)s(-1)) conditions. Some of the plants were kept at 20/18 degrees C for 12 days at high light intensity (500 micromol m(-2)s(-1)), which also increased the freezing tolerance of winter wheat. The freezing survival rate, the lipid composition, the antioxidant activity, and the salicylic acid content were investigated during frost hardening. The saturation level of hexadecanoic acid decreased not only in plants hardened at low temperature, but also, to a lesser extent, in plants kept under high light irradiation at normal growth temperature. The greatest induction of the enzymes glutathione reductase (EC 1.6.4.2.) and ascorbate peroxidase (EC 1.11.1.11.) occurred when the cold treatment was carried out in normal light, but high light intensity at normal, non-hardening temperature also increased the activity of these enzymes. The catalase (EC 1.11.1.6.) activity was also higher in plants grown at high light intensity than in the controls. The greatest level of induction in the activity of the guaiacol peroxidase (EC 1.11.1.7.) enzyme occurred under cold conditions with low light. The bound ortho-hydroxy-cinnamic acid increased by up to two orders of magnitude in plants that were cold hardened in normal light. Both high light intensity and low temperature hardening caused an increase in the free and bound salicylic acid content of the leaves. This increase was most pronounced in plants that were cold treated in normal light.

Environmental and hormonal regulation of the activity-dormancy cycle in the cambial meristem involves stage-specific modulation of transcriptional and metabolic networks

We have performed transcript and metabolite profiling of isolated cambial meristem cells of the model tree aspen during the course of their activity-dormancy cycle to better understand the environmental and hormonal regulation of this process in perennial plants. Considerable modulation of cambial transcriptome and metabolome occurs throughout the activity-dormancy cycle. However, in addition to transcription, post-transcriptional control is also an important regulatory mechanism as exemplified by the regulation of cell-cycle genes during the reactivation of cambial cell division in the spring. Genes related to cold hardiness display temporally distinct induction patterns in the autumn which could explain the step-wise development of cold hardiness. Factors other than low temperature regulate the induction of early cold hardiness-related genes whereas abscisic acid (ABA) could potentially regulate the induction of late cold hardiness-related genes in the autumn. Starch breakdown in the autumn appears to be regulated by the 'short day' signal and plays a key role in providing substrates for the production of energy, fatty acids and cryoprotectants. Catabolism of sucrose and fats provides energy during the early stages of reactivation in the spring, whereas the reducing equivalents are generated through activation of the pentose phosphate shunt. Modulation of gibberellin (GA) signaling and biosynthesis could play a key role in the regulation of cambial activity during the activity-dormancy cycle as suggested by the induction of PttRGA which encodes a negative regulator of growth in the autumn and that of a GA-20 oxidase, a key gibberellin biosynthesis gene during reactivation in spring. In summary, our data reveal the dynamics of transcriptional and metabolic networks and identify potential targets of environmental and hormonal signals in the regulation of the activity-dormancy cycle in cambial meristem.

Enhancing salt tolerance in a crop plant by overexpression of glyoxalase II

Earlier we have shown the role of glyoxalase overexpression in conferring salinity tolerance in transgenic tobacco. We now demonstrate the feasibility of same in a crop like rice through overproduction of glyoxalase II. The rice glyoxalase II was cloned in pCAMBIA1304 and transformed into rice (Oryza sativa cv PB1) via Agrobacterium. The transgenic plants showed higher constitutive activity of glyoxalase II that increased further upon salt stress, reflecting the upregulation of endogenous glyoxalase II. The transgenic rice showed higher tolerance to toxic concentrations of methylglyoxal (MG) and NaCl. Compared with non-transgenics, transgenic plants at the T1 generation exhibited sustained growth and more favorable ion balance under salt stress conditions.

Mitochondrial retrograde regulation in plants

Plant cells must react to a variety of adverse environmental conditions that they may experience on a regular basis. Part of this response centers around (1) ROS as damaging molecules and signaling molecules; (2) redox status, which can be influenced by ROS production; and (3) availability of metabolites. All of these are also likely to interface with changes in hormone levels [Desikan, R., Hancock, J., Neill, S., 2005. Reactive oxygen species as signalling molecules. In: Smirnoff, N. (ed.), Antioxidants and reactive oxygen species in plants. Blackwell Pub. Ltd., Oxford, pp. 169-196; Kwak, J.M., Nguyen, V., Schroeder, J.I., 2006. The role of reactive oxygen species in hormonal responses. Plant Physiol. 141, 323-329]. Each of these areas can be strongly influenced by changes in mitochondrial function. Such changes trigger altered nuclear gene expression by a poorly understood process of mitochondrial retrograde regulation (MRR), which is likely composed of several distinct signaling pathways. Much of what is known about plant MRR centers around the response to a dysfunctional mtETC and subsequent induction of genes encoding proteins involved in recovery of mitochondrial functions, such as AOX and alternative NAD(P)H dehydrogenases, and genes encoding enzymes aimed at regaining ROS level/redox homeostasis, such as glutathione transferases, catalases, ascorbate peroxidases and superoxide dismutases. However, as evidence of new and interesting targets of MRR emerge, this picture is likely to change and the complexity and importance of MRR in plant responses to stresses and the decision for cells to either recover or switch into programmed cell death mode is likely to become more apparent.

Co-ordinated gene expression during phases of dormancy release in raspberry (Rubus idaeus L.) buds

Bud break in raspberry (Rubus idaeus L.) is often poor and uneven, with many of the subapical buds remaining in a dormant state. In order to determine the dormancy status of raspberry buds, an empirical measure of bud burst in a growth-permissive environment following exposure to chilling (4 degrees C cold storage) was developed. For cv. Glen Ample, percentage bud burst in intact canes and isolated nodes was recorded after 14 d. Isolated nodes (a measure of endodormancy) achieved 100% bud burst after approximately 1500 h chilling whereas buds on intact plants (combined endo- and paradormancy) required an additional 1000 h chilling. A microarray approach was used to follow changes in gene expression that occurred during dormancy transition. The probes for the microarrays were obtained from endodormant and paradormant raspberry bud cDNA libraries. The expression profiles of 5300 clones from these libraries were subjected to principal component analysis to determine the most significant expression patterns. Sequence analysis of these clones, in many cases, enabled their functional categorization and the development of hypotheses concerning the mechanisms of bud dormancy release. Thus a set of novel candidates for key dormancy-related genes from raspberry buds have been identified. Bud dormancy is fundamental to the study of plant developmental processes and, in addition, its regulation is of significant economic importance to fruit and horticultural industries.

Methyl jasmonate and salicylic acid elicitation induces ginsenosides accumulation, enzymatic and non-enzymatic antioxidant in suspension culture Panax ginseng roots in bioreactors

The effects of methyl jasmonate (MJ) and salicylic acid (SA) on changes of the activities of major antioxidant enzymes, superoxide anion accumulation (O2-), ascorbate, total glutathione (TG), malondialdehyde (MDA) content and ginsenoside accumulation were investigated in ginseng roots (Panax ginseng L.) in 4 l (working volume) air lift bioreactors. Single treatment of 200 microM MJ and SA to P. ginseng roots enhanced ginsenoside accumulation compared to the control and harvested 3, 5, 7 and 9 days after treatment. MJ and SA treatment induced an oxidative stress in P. ginseng roots, as shown by an increase in lipid peroxidation due to rise in O2- accumulation. Activity of superoxide dismutase (SOD) was inhibited in MJ-treated roots, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), SOD, guaiacol peroxidase (G-POD), glutathione peroxidase (GPx) and glutathione reductase (GR) were induced in SA-treated roots. A strong decrease in the activity of catalase (CAT) was obtained in both MJ- and SA-treated roots. Activities of ascorbate peroxidase (APX) and glutathione S transferase (GST) were higher in MJ than SA while the contents of reduced ascorbate (ASC), redox state (ASC/(ASC+DHA)) and TG were higher in SA- than MJ-treated roots while oxidized ascorbate (DHA) decreased in both cases. The result of these analyses suggests that roots are better protected against the O2- stress, thus mitigating MJ and SA stress. The information obtained in this work is useful for efficient large-scale production of ginsenoside by plant-root cultures.

Regulation of sulfate assimilation in Arabidopsis and beyond

BACKGROUND AND AIMS

Sulfate assimilation is a pathway used by prokaryotes, fungi and photosynthetic organisms to convert inorganic sulfate to sulfide, which is further incorporated into carbon skeletons of amino acids to form cysteine or homocysteine. The pathway is highly regulated in a demand-driven manner; however, this regulation is not necessarily identical in various plant species. Therefore, our knowledge of the regulation of sulfate assimilation is reviewed here in detail with emphasis on different plant species.

SCOPE

Although demand-driven control plays an essential role in regulation of sulfate assimilation in all plants, the molecular mechanisms of the regulation and the effects of various treatments on the individual enzymes and metabolites are often different. This review summarizes (1) the molecular regulation of sulfate assimilation in Arabidopsis thaliana, especially recent data derived from platform technologies and functional genomics, (2) the co-ordination of sulfate, nitrate and carbon assimilations in Lemna minor, (3) the role of sulfate assimilation and glutathione in plant-Rhizobia symbiosis, (4) the cell-specific distribution of sulfate reduction and glutathione synthesis in C(4) plants, (5) the regulation of glutathione biosynthesis in poplar, (6) the knock-out of the adenosine 5'phosphosulfate reductase gene in Physcomitrella patens and identification of 3'-phosphoadenosyl 5'-phosphosulfate reductase in plants, and (7) the sulfur sensing mechanism in green algae.

CONCLUSIONS

As the molecular mechanisms of regulation of the sulfate assimilation pathway are not known, the role of Arabidopsis as a model plant will be further strengthened. However, this review demonstrates that investigations of other plant species will still be necessary to address specific questions of regulation of sulfur nutrition.

Heat-induced oxidative activity protects suspension-cultured plant cells from low temperature damage

A short heat pre-treatment (1 h at 38°C) was found to protect both suspension-cultured apple fruit cells and tobacco cells from cold-induced cell death. Tobacco cells were more sensitive to low temperatures than apple cells, with significant cell death after 48 h at 0 or -2°C. Real-time measurements of H₂O₂ levels during the heat pre-treatment revealed a substantial burst of this reactive oxygen species in both cell types. Real-time and longer-term measurements also showed a large burst of H₂O₂ production from tobacco cells, but not apple cells, when exposed to low temperatures. Lower temperatures reduced levels of peroxidase activity (both total and intracellular), with the heat pre-treatment preventing some of the cold-induced reduction of this activity in both apple and tobacco cells. The greater sensitivity to low temperature of the tobacco cells may be related to higher H₂O₂ production, with the heat treatment maintaining higher peroxidase activity. The lesser sensitivity of the apple cells may be due to the lack of a H₂O₂ burst and maintenance of peroxidase activity by the heat treatment. These results support a role for oxidative metabolism in the beneficial effects of heat in inducing low temperature tolerance.

Sulfate assimilation and glutathione synthesis in C4 plants

Sulfate assimilation and glutathione synthesis were traditionally believed to be differentially compartmentalised in C4 plants with the synthesis of cysteine and glutathione restricted to bundle sheath and mesophyll cells, respectively. Recent studies, however, showed that although ATP sulfurylase and adenosine 5' phosphosulfate reductase, the key enzymes of sulfate assimilation, are localised exclusively in bundle sheath in maize and other C4 monocot species, this is not true for the dicot C4 species of Flaveria. On the other hand, enzymes of glutathione biosynthesis were demonstrated to be active in both types of maize cells. Therefore, in this review the recent findings on compartmentation of sulfate assimilation and glutathione metabolism in C4 plants will be summarised and the consequences for our understanding of sulfate metabolism and C4 photosynthesis will be discussed.

Transgenic tobacco plants overexpressing glyoxalase enzymes resist an increase in methylglyoxal and maintain higher reduced glutathione levels under salinity stress

The mechanism behind enhanced salt tolerance conferred by the overexpression of glyoxalase pathway enzymes was studied in transgenic vis-à-vis wild-type (WT) plants. We have recently documented that salinity stress induces higher level accumulation of methylglyoxal (MG), a potent cytotoxin and primary substrate for glyoxalase pathway, in various plant species [Yadav, S.K., Singla-Pareek, S.L., Ray, M., Reddy, M.K. and Sopory, S.K. (2005) MG levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 337, 61-67]. The transgenic tobacco plants overexpressing glyoxalase pathway enzymes, resist an increase in the level of MG that increased to over 70% in WT plants under salinity stress. These plants showed enhanced basal activity of various glutathione related antioxidative enzymes that increased further upon salinity stress. These plants suffered minimal salinity stress induced oxidative damage measured in terms of the lipid peroxidation. The reduced glutathione (GSH) content was high in these transgenic plants and also maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio under salinity. Manipulation of glutathione ratio by exogenous application of GSSG retarded the growth of non-transgenic plants whereas transgenic plants sustained their growth. These results suggest that resisting an increase in MG together with maintaining higher reduced glutathione levels can be efficiently achieved by the overexpression of glyoxalase pathway enzymes towards developing salinity stress tolerant plants.

Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis

This paper reviews the potential of trace/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the following reasons: (1) Heavy metals change membrane properties through impaired resource acquisition and subsequent diminution of the cryoprotectant pool. (2) Heavy metals change membrane properties directly through oxidative stress, i.e. an increase of active oxygen species. (3) The involved co-stress may further increase oxidative stress. (4) The risk of frost injury increases due to membrane alterations. An opposite perspective was also discussed: could metal stress result in enhanced plant frost hardiness? This phenomenon could be based on the metabolism (i.e. glutathione, polyamines, proline, heat shock proteins) underlying a possible general adaptation syndrome of stress (GAS). As a result of the review it was suggested that metal-induced stress seems to reduce rather than increase plant frost hardiness.

Tea (Camellia sinensis (L.) O. Kuntze) clone with lower period of winter dormancy exhibits lesser cellular damage in response to low temperature

There is no literature available on the response of tea plant to low temperature. We studied the effect of low temperature on two clones of tea with contrasting periods of winter dormancy, a phenomenon in which the growth of apical shoots of tea is diminished during winter months. Clone 'Teenali 17/154' (TNL) showed shorter periods of winter dormancy than clone 'Kangra Jat' (KNJ). Low temperature (5 degrees C) resulted in increase of metabolic superoxide (O2*-) content and cellular damage (as measured by tetrazolium chloride reduction test) in both the clones, however, the increase was lesser in the case of TNL compared to KNJ. Activities of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) increased in both the clones in response to low temperature however, GR activity exhibited significant differences (P < 0.05) between the two clones. Low temperature caused increase in the intensity of various isozymes of SOD, APX and GR. A new isozyme of SOD (Cu/Zn type) was induced in both the clones at low temperature. Significantly higher GR activity in both the clones suggested a role of this enzyme in imparting better protection to tea at low temperature. Also, clonal variation for GR isozyme was observed between the clones. Based on these results it appears that TNL, a clone with relatively lesser period of winter dormancy experiences lesser oxidative stress in response to low temperature compared to KNJ, a clone with relatively higher period of winter dormancy.

Field trial of transgenic Indian mustard plants shows enhanced phytoremediation of selenium-contaminated sediment

Three transgenic Indian mustard [Brassica juncea (L.) Czern.] lines were tested under field conditions for their ability to remove selenium (Se) from Se- and boron-contaminated saline sediment. The transgenic lines overexpressed genes encoding the enzymes adenosine triphosphate sulfurylase (APS), gamma-glutamyl-cysteine synthetase (ECS), and glutathione synthetase (GS), respectively. The APS, ECS, and GS transgenic plants accumulated 4.3, 2.8, and 2.3-fold more Se in their leaves than wild type, respectively (P < 0.05). GS plants significantly tolerated the contaminated soil better than wild type, attaining an aboveground biomass/area almost 80% of that of GS plants grown on clean soil, compared to 50% for wild type plants. This is the first report showing that plants genetically engineered for phytoremediation can perform successfully under field conditions.

Cambial meristem dormancy in trees involves extensive remodelling of the transcriptome

The establishment of the dormant state in meristems involves considerable physiological and metabolic alterations necessary for surviving unfavourable growth conditions. However, a global molecular analysis of dormancy in meristems has been hampered by the difficulty in isolating meristem cells. We used cryosectioning to isolate purified cambial meristem cells from the woody plant Populus tremula during active growth and dormancy. These samples were used to generate meristem-specific cDNA libraries and for cDNA microarray experiments to define the global transcriptional changes underlying cambial dormancy. The results indicate a significant reduction in the complexity of the cambial transcriptome in the dormant state. Although cell division is terminated in the dormant cambium, the cell cycle machinery appears to be maintained in a skeletal state as suggested by the continued presence of transcripts for several cell cycle regulators. The downregulation of PttPIN1 and PttPIN2 transcripts explains the reduced basipetal polar auxin transport during dormancy. The induction of a member of the SINA family of ubiquitin ligases implicated in auxin signalling indicates a potential mechanism for modulation of auxin sensitivity during cambial dormancy. The metabolic alterations during dormancy are mirrored in the induction of genes involved in starch breakdown and the glyoxysomal cycle. Interestingly, the induction of RGA1 like gene suggests modification of gibberellin signalling in cambial dormancy. The induction of genes such as poplar orthologues of FIE and HAP2 indicates a potential role for these global regulators of transcription in orchestrating extensive changes in gene expression during dormancy.

Antioxidative responses of Calendula officinalis under salinity conditions

To gain a better insight into long-term salt-induced oxidative stress, some physiological parameters in marigold (Calendula officinalis L.) under 0, 50 and 100 mM NaCl were investigated. Salinity affected most of the considered parameters. High salinity caused reduction in growth parameters, lipid peroxidation and hydrogen peroxide accumulation. Under high salinity stress, a decrease in total glutathione and an increase in total ascorbate (AsA + DHA), accompanied with enhanced glutathione reductase (GR, EC 1.6.4.2) and ascorbate peroxidase (APX, EC 1.11.1.11) activities, were observed in leaves. In addition, salinity induced a decrease in superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POX, EC 1.11.1.7) activities. The decrease in dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities suggests that other mechanisms play a major role in the regeneration of reduced ascorbate. The changes in catalase (CAT, EC 1.11.1.6) activities, both in roots and in leaves, may be important in H2O2 homeostasis.

Effect of osmotic stress on glutathione and hydroxymethylglutathione accumulation in wheat

The effect of osmotic stress on glutathione and hydroxymethylglutathione levels was compared in three wheat genotypes and two 5A chromosome substitution lines. Freezing-tolerant genotypes seemed also to be tolerant to osmotic stress induced by polyethylene glycol (PEG), since their fresh weight was not affected by the treatment. However, the growth of freezing-sensitive genotypes was reduced by 7-day PEG treatment and they had greater injuries after osmotic stress. The reduced forms of the two glutathione precursors, cysteine and gamma-glutamylcysteine, and of hydroxymethylglutathione (hmGSH) and glutathione (GSH) were present in greater quantities after PEG treatment in the two tolerant genotypes than in the sensitive ones. Similarly, osmotic stress resulted in a higher ratio of the reduced to the oxidised form of these thiols and in greater activity of gamma-glutamylcysteine synthetase and glutathione reductase in the tolerant genotypes compared to the sensitive ones. Following in vivo glutathione synthesis, a greater incorporation of radioactivity from [35S]sulphate into the four thiols was found in the tolerant genotypes than in the sensitive ones during osmotic stress. The present results indicate that hmGSH and GSH may contribute to the improvement of tolerance against osmotic stress in wheat and that the 5A chromosome influences the stress-induced changes in GSH and hmGSH levels.

Intercellular distribution of glutathione synthesis in maize leaves and its response to short-term chilling

To investigate the intercellular control of glutathione synthesis and its influence on leaf redox state in response to short-term chilling, genes encoding gamma-glutamylcysteine synthetase (gamma-ECS) and glutathione synthetase (GSH-S) were cloned from maize (Zea mays) and specific antibodies produced. These tools were used to provide the first information on the intercellular distribution of gamma-ECS and GSH-S transcript and protein in maize leaves, in both optimal conditions and chilling stress. A 2-d exposure to low growth temperatures (chill) had no effect on leaf phenotype, whereas return to optimal temperatures (recovery) caused extensive leaf bleaching. The chill did not affect total leaf GSH-S transcripts but strongly induced gamma-ECS mRNA, an effect reversed during recovery. The chilling-induced increase in gamma-ECS transcripts was not accompanied by enhanced total leaf gamma-ECS protein or extractable activity. In situ hybridization and immunolocalization of leaf sections showed that gamma-ECS and GSH-S transcripts and proteins were found in both the bundle sheath (BS) and the mesophyll cells under optimal conditions. Chilling increased gamma-ECS transcript and protein in the BS but not in the mesophyll cells. Increased BS gamma-ECS was correlated with a 2-fold increase in both leaf Cys and gamma-glutamylcysteine, but leaf total glutathione significantly increased only in the recovery period, when the reduced glutathione to glutathione disulfide ratio decreased 3-fold. Thus, while there was a specific increase in the potential contribution of the BS cells to glutathione synthesis during chilling, it did not result in enhanced leaf glutathione accumulation at low temperatures. Return to optimal temperatures allowed glutathione to increase, particularly glutathione disulfide, and this was associated with leaf chlorosis.

Nitric oxide acts as an antioxidant and delays methyl jasmonate-induced senescence of rice leaves

In the present study, we evaluate the protective effect of nitric oxide (NO) against senescence of rice leaves promoted by methyl jasmonate (MJ). Senescence of rice leaves was determined by the decrease of protein content. MJ treatment resulted in (1) induction of leaf senescence, (2) increase in H2O2 and malondialdehyde (MDA) contents, (3) decrease in reduced form glutathione (GSH) and ascorbic acid (AsA) contents, and (4) increase in antioxidative enzyme activities (ascorbate peroxidase, glutathione reductase, peroxidase and catalase). All these MJ effects were reduced by free radical scavengers such as sodium benzoate and GSH. NO donors [N-tert-butyl-alpha-phenylnitrone (PBN), sodium nitroprusside, 3-morpholinosydonimine, and AsA+NaNO2] were effective in reducing MJ-induced leaf senescence. PBN prevented MJ-induced increase in the contents of H2O2 and MDA, decrease in the contents of GSH and AsA, and increase in the activities of antioxidative enzymes. The protective effect of PBN on MJ-promoted senescence, MJ-increased H2O2 content and lipid peroxidation, MJ-decreased GSH and AsA, and MJ-increased antioxidative enzyme activities was reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO-specific scavenger, suggesting that the protective effect of PBN is attributable to NO released. Reduction of MJ-induced senescence by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H2O2.

Aluminium-responsive genes in sugarcane: identification and analysis of expression under oxidative stress

Suppression subtractive hybridization (SSH) technology was used to gain preliminary insights into gene expression induced by the phytotoxic aluminium species, Al(3+), in sugarcane roots. Roots of hydroponically-grown Saccharum spp. hybrid cv. N19 were exposed to 221 microM Al(3+) at pH 4.1 for 24 h, a regime shown to inhibit root elongation by 43%, relative to unchallenged roots. Database comparisons revealed that, of a subset of 50 cDNAs ostensibly up-regulated by the metal in the root tips, 14 possessed putative identities indicative of involvement in signalling events and the regulation of gene expression, while the majority (28) were of unknown function. All of the 50 cDNAs sequenced displayed significant similarity to uncharacterized plant expressed sequence tags (ESTs), approximately half (23) of which had been derived from other graminaceous crop species that had been subject to a variety of stresses. Analysis of the expression of 288 putative Al(3+)-inducible genic fragments indicated higher levels of expression under oxidative (1 mM diamide for 4 h) rather than Al(3+) stress. By deploying SSH, this study has provided an indication of the nature of genes expressed in sugarcane roots under Al(3+) stress. It is anticipated that the information obtained will guide further exploration of the potential for manipulation of the Al tolerance characteristics of the crop.

Mammalian cell injury induced by hypothermia- the emerging role for reactive oxygen species

Hypothermia is a well-known strategem to protect biological material against injurious or degradative processes and is widely used in experimental and especially in clinical applications. However, hypothermia has also proved to be strongly injurious to a variety of cell types. Hypothermic injury to mammalian cells has long been attributed predominantly to disturbances of cellular ion homeostasis, especially of sodium homeostasis. For many years, reactive oxygen species have hardly been considered in the pathogenesis of hypothermic injury to mammalian cells. In recent years, however, increasing evidence for a role of reactive oxygen species in hypothermic injury to these cells has accumulated. Today there seems to be little doubt that reactive oxygen species decisively contribute to hypothermic injury in diverse mammalian cells. In some cell types, such as liver and kidney cells, they even appear to play the central role in hypothermic injury, outruling by far a contribution of the cellular ion homeostasis. In these cells, the cellular chelatable, redox-active iron pool appears to be decisively involved in the pathogenesis of hypothermic injury and of cold-induced apoptosis that occurs upon rewarming of the cells after a (sublethal) period of cold incubation.