An inhibitor of catalase induced by cold in chilling-sensitive plants

Rippling life on a dormant planet: hibernation of ribosomes, RNA polymerases, and other essential enzymes

Throughout the tree of life, cells and organisms enter states of dormancy or hibernation as a key feature of their biology: from a bacterium arresting its growth in response to starvation, to a plant seed anticipating placement in fertile ground, to a human oocyte poised for fertilization to create a new life. Recent research shows that when cells hibernate, many of their essential enzymes hibernate too: they disengage from their substrates and associate with a specialized group of proteins known as hibernation factors. Here, we summarize how hibernation factors protect essential cellular enzymes from undesired activity or irreparable damage in hibernating cells. We show how molecular hibernation, once viewed as rare and exclusive to certain molecules like ribosomes, is in fact a widespread property of biological molecules that is required for the sustained persistence of life on Earth.

Regulating Effect of Exogenous α-Ketoglutarate on Ammonium Assimilation in Poplar

Extensive industrial activities and anthropogenic agricultural practices have led to substantial ammonia release to the environment. Although croplands can act as ammonia sinks, reduced crop production under high concentrations of ammonium has been documented. Alpha-ketoglutarate (AKG) is a critical carbon source, displaying pleiotropic physiological functions. The objective of the present study is to disclose the potential of AKG to enhance ammonium assimilation in poplars. It showed that AKG application substantially boosted the height, biomass, and photosynthesis activity of poplars exposed to excessive ammonium. AKG also enhanced the activities of key enzymes involved in nitrogen assimilation: glutamine synthetase (GS) and glutamate synthase (GOGAT), elevating the content of amino acids, sucrose, and the tricarboxylic acid cycle (TCA) metabolites. Furthermore, AKG positively modulated key genes tied to glucose metabolism and ATP synthesis, while suppressing ATP-depleting genes. Correspondingly, both H+-ATPase activity and ATP content increased. These findings demonstrate that exogenously applying AKG improves poplar growth under a high level of ammonium treatment. AKG might function through sufficient carbon investment, which enhances the carbon-nitrogen balance and energy stability in poplars, promoting ammonium assimilation at high doses of ammonium. Our study provides novel insight into AKG's role in improving poplar growth in response to excess ammonia exposure.

A new family of bacterial ribosome hibernation factors

To conserve energy during starvation and stress, many organisms use hibernation factor proteins to inhibit protein synthesis and protect their ribosomes from damage1,2. In bacteria, two families of hibernation factors have been described, but the low conservation of these proteins and the huge diversity of species, habitats and environmental stressors have confounded their discovery3-6. Here, by combining cryogenic electron microscopy, genetics and biochemistry, we identify Balon, a new hibernation factor in the cold-adapted bacterium Psychrobacter urativorans. We show that Balon is a distant homologue of the archaeo-eukaryotic translation factor aeRF1 and is found in 20% of representative bacteria. During cold shock or stationary phase, Balon occupies the ribosomal A site in both vacant and actively translating ribosomes in complex with EF-Tu, highlighting an unexpected role for EF-Tu in the cellular stress response. Unlike typical A-site substrates, Balon binds to ribosomes in an mRNA-independent manner, initiating a new mode of ribosome hibernation that can commence while ribosomes are still engaged in protein synthesis. Our work suggests that Balon-EF-Tu-regulated ribosome hibernation is a ubiquitous bacterial stress-response mechanism, and we demonstrate that putative Balon homologues in Mycobacteria bind to ribosomes in a similar fashion. This finding calls for a revision of the current model of ribosome hibernation inferred from common model organisms and holds numerous implications for how we understand and study ribosome hibernation.

Moderate modulation by S-nitrosoglutathione of photorespiratory enzymes in pea (Pisum sativum) leaves, compared to the strong effects of high light

When plants are exposed to water stress, photosynthesis is downregulated due to enhanced reactive oxygen species (ROS) and nitric oxide (NO). In contrast, photorespiratory metabolism protected photosynthesis and sustained yield. Modulation of photorespiration by ROS was established, but the effect of NO on photorespiratory metabolism was unclear. We, therefore, examined the impact of externally added NO by using S-nitrosoglutathione (GSNO), a natural NO donor, in leaf discs of pea (Pisum sativum) under dark or light: moderate or high light (HL). Maximum NO accumulation with GSNO was under high light. The presence of 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO scavenger, prevented the increase in NO, confirming the release of NO in leaves. The increase in S-nitrosothiols and tyrosine-nitrated proteins on exposure to GSNO confirmed the nitrosative stress in leaves. However, the changes by GSNO in the activities and transcripts of five photorespiratory enzymes: glycolate oxidase, hydroxypyruvate reductase, catalase, glycerate kinase, and phosphoglycolate phosphatase activities were marginal. The changes in photorespiratory enzymes caused by GSNO were much less than those with HL. Since GSNO caused only mild oxidative stress, we felt that the key modulator of photorespiration might be ROS, but not NO.

Measurement of Photorespiratory Cycle Enzyme Activities in Leaves Exposed to Abiotic Stress

Photorespiration, an essential metabolic component, is a classic example of interactions between the intracellular compartments of a plant cell: the chloroplast, peroxisome, mitochondria, and cytoplasm. The photorespiratory pathway is often modulated by abiotic stress and is considered an adaptive response. Monitoring the patterns of key enzymes located in different subcellular components would be an ideal approach to assessing the modulation of the photorespiratory metabolism under abiotic stress. This chapter describes the procedures for assaying several individual enzyme activities of key photorespiratory enzymes and evaluating their response to oxidative/photooxidative stress. It is essential to ascertain the presence of stress in the experimental material. Therefore, procedures for typical abiotic stress induction in leaves by highlighting without or with menadione (an oxidant that targets mitochondria) are also included.

Suppression of photorespiratory metabolism by low O2 and presence of aminooxyacetic acid induces oxidative stress in Arabidopsis thaliana leaves

Photorespiration, an essential component of plant metabolism, was upregulated under abiotic stress conditions, such as high light or drought. One of the signals for such upregulation was the rise in reactive oxygen species (ROS). Photorespiration was expected to mitigate oxidative stress by reducing ROS levels. However, it was unclear if ROS levels would increase when photorespiration was lowered. Our goal was to examine the redox status in leaves when photorespiratory metabolism was restricted under low O2 (medium flushed with N2 gas) or by adding aminooxyacetic acid (AOA), a photorespiratory inhibitor. We examined the impact of low O2 and AOA in leaves of Arabidopsis thaliana under dark, moderate, or high light. Downregulation of typical photorespiratory enzymes, including catalase (CAT), glycolate oxidase (GO), and phosphoglycolate phosphatase (PGLP) under low O2 or with AOA confirmed the lowering of photorespiratory metabolism. A marked increase in ROS levels (superoxide and H2O2) indicated the induction of oxidative stress. Thus, our results demonstrated for the first time that restricted photorespiratory conditions increased the extent of oxidative stress. We propose that photorespiration is essential to sustain normal ROS levels and optimize metabolism in cellular compartments of Arabidopsis leaves.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01388-4.

Metabolic pathways modulated by coumarin to inhibit seed germination and early seedling growth in Eleusine indica

Coumarin is an allelochemical that is widely present in the plant kingdom and has great potential for weed control. However, its mechanisms of action remain largely unknown. This study employed metabolomic and transcriptomic analyses along with evaluations of amino acid profiles and related physiological indicators to investigate how coumarin inhibits the germination and seedling growth of Eleusine indica by modifying metabolic pathways. At 72 h of germination at 50 and 100 mg L-1 coumarin, E. indica had lower levels of soluble sugar and activities of amylases and higher levels of starch, O2-, H2O2, auxin (IAA) and abscisic acid (ABA) compared to the control. Metabolomic analysis demonstrated that coumarin treatments had a significant impact on the pathways associated with amino acid metabolism and transport and aminoacyl-tRNA biosynthesis. Exposure to coumarin induced significant alterations in the levels of 19 amino acids, with a decrease in 15 of them, including Met, Leu and γ-aminobutyric acid (GABA). Additionally, transcriptomic analysis showed that coumarin significantly disrupted several essential biological processes, including protein translation, secondary metabolite synthesis, and hormone signal transduction. The decrease in TCA cycle metabolite (cis-aconitate, 2-oxoglutarate, and malate) contents was associated with the suppression of transcription for related enzymes. Our findings indicate that the inhibition of germination and growth in E. indica by coumarin involves the suppression of starch conversion to sugars, modification of the amino acid profile, interference of hormone signalling and the induction of oxidative stress. The TCA cycle appears to be one of the most essential pathways affected by coumarin.

Redox basis of photosynthesis inhibition at supra-optimal bicarbonate in mesophyll protoplasts of Arabidopsis thaliana

We examined the patterns of photosynthetic O2 evolution at 1 mM (optimal) and 10 mM (supra-optimal) bicarbonate in mesophyll protoplasts of Arabidopsis thaliana. The photosynthetic rate of protoplasts reached the maximum at an optimal concentration of 1 mM bicarbonate and got suppressed at supra-optimal levels of bicarbonate. We examined the basis of such photosynthesis inhibition by mesophyll protoplasts at supra-optimal bicarbonate. The wild-type protoplasts exposed to supra-optimal bicarbonate showed up signs of oxidative stress. Besides the wild-type, two mutants were used: nadp-mdh (deficient in chloroplastic NADP-MDH) and vtc1 (deficient in mitochondrial ascorbate biosynthesis). The protoplasts of the nadp-mdh mutant exhibited a higher photosynthetic rate and greater sensitivity to supra-optimal bicarbonate than the wild-type. The ascorbate-deficient vtc1 mutant had a low photosynthetic rate and no significant inhibition at high bicarbonate. The nadp-mdh mutants had elevated activities, protein, and transcript levels of key antioxidant enzymes. On the other hand, the antioxidant enzyme systems in vtc1 mutants were not much affected at supra-optimal bicarbonate. We propose that the inhibition of photosynthesis at supra-optimal bicarbonate depends on the redox state of mesophyll protoplasts. The robust antioxidant enzyme systems in protoplasts of nadp-mdh mutant might be priming the plants to sustain high photosynthesis at supra-optimal bicarbonate.

Reversible changes in structure and function of photosynthetic apparatus of pea (Pisum sativum) leaves under drought stress

The effects of drought on photosynthesis have been extensively studied, whereas those on thylakoid organization are limited. We observed a significant decline in gas exchange parameters of pea (Pisum sativum) leaves under progressive drought stress. Chl a fluorescence kinetics revealed the reduction of photochemical efficiency of photosystem (PS)II and PSI. The non-photochemical quenching (NPQ) and the levels of PSII subunit PSBS increased. Furthermore, the light-harvesting complexes (LHCs) and some of the PSI and PSII core proteins were disassembled in drought conditions, whereas these complexes were reassociated during recovery. By contrast, the abundance of supercomplexes of PSII-LHCII and PSII dimer were reduced, whereas LHCII monomers increased following the change in the macro-organization of thylakoids. The stacks of thylakoids were loosely arranged in drought-affected plants, which could be attributed to changes in the supercomplexes of thylakoids. Severe drought stress caused a reduction of both LHCI and LHCII and a few reaction center proteins of PSI and PSII, indicating significant disorganization of the photosynthetic machinery. After 7 days of rewatering, plants recovered well, with restored chloroplast thylakoid structure and photosynthetic efficiency. The correlation of structural changes with leaf reactive oxygen species levels indicated that these changes were associated with the production of reactive oxygen species.

Influence of Schumann Range Electromagnetic Fields on Components of Plant Redox Metabolism in Wheat and Peas

The Schumann Resonances (ScR) are Extremely Low Frequency (ELF) electromagnetic resonances in the Earth-ionosphere cavity excited by global lightning discharges. ScR are the part of electromagnetic field (EMF) of Earth. The influence of ScR on biological systems is still insufficiently understood. The purpose of the study is to characterize the possible role of the plant cell redox metabolism regulating system in the Schumann Resonances EMF perception. Activity of catalase and superoxide dismutase, their isoenzyme structure, content of malondialdehyde, composition of polar lipids in leaf extracts of wheat and pea plants treated with short-time (30 min) and long-time (18 days) ELF EMF with a frequency of 7.8 Hz, 14.3 Hz, 20.8 Hz have been investigated. Short-time exposure ELF EMF caused more pronounced bio effects than long-time exposure. Wheat catalase turned out to be the most sensitive parameter to magnetic fields. It is assumed that the change in the activity of wheat catalase after a short-term ELF EMF may be associated with the ability of this enzyme to perceive the action of a weak EMF through calcium calmodulin and/or cryptochromic signaling systems.

Comparative transcriptome analysis of heat stress responses of Clematis lanuginosa and Clematis crassifolia

BACKGROUND

Clematis species are attractive ornamental plants with a variety of flower colors and patterns. Heat stress is one of the main factors restricting the growth, development, and ornamental value of Clematis. Clematis lanuginosa and Clematis crassifolia are large-flowered and evergreen Clematis species, respectively, that show different tolerance to heat stress. We compared and analyzed the transcriptome of C. lanuginose and C. crassifolia under heat stress to determine the regulatory mechanism(s) of resistance.

RESULTS

A total of 1720 and 6178 differentially expressed genes were identified from C. lanuginose and C. crassifolia, respectively. The photosynthesis and oxidation-reduction processes of C. crassifolia were more sensitive than C. lanuginose under heat stress. Glycine/serine/threonine metabolism, glyoxylic metabolism, and thiamine metabolism were important pathways in response to heat stress in C. lanuginose, and flavonoid biosynthesis, phenylalanine metabolism, and arginine/proline metabolism were the key pathways in C. crassifolia. Six sHSPs (c176964_g1, c200771_g1, c204924_g1, c199407_g2, c201522_g2, c192936_g1), POD1 (c200317_g1), POD3 (c210145_g2), DREB2 (c182557_g1), and HSFA2 (c206233_g2) may be key genes in the response to heat stress in C. lanuginose and C. crassifolia.

CONCLUSIONS

We compared important metabolic pathways and differentially expressed genes in response to heat stress between C. lanuginose and C. crassifolia. The results increase our understanding of the response mechanism and candidate genes of Clematis under heat stress. These data may contribute to the development of new Clematis varieties with greater heat tolerance.

Modulation of Photorespiratory Enzymes by Oxidative and Photo-Oxidative Stress Induced by Menadione in Leaves of Pea (Pisum sativum)

Photorespiration, an essential component of plant metabolism, is concerted across four subcellular compartments, namely, chloroplast, peroxisome, mitochondrion, and the cytoplasm. It is unclear how the pathway located in different subcellular compartments respond to stress occurring exclusively in one of those. We attempted to assess the inter-organelle interaction during the photorespiratory pathway. For that purpose, we induced oxidative stress by menadione (MD) in mitochondria and photo-oxidative stress (high light) in chloroplasts. Subsequently, we examined the changes in selected photorespiratory enzymes, known to be located in other subcellular compartments. The presence of MD upregulated the transcript and protein levels of five chosen photorespiratory enzymes in both normal and high light. Peroxisomal glycolate oxidase and catalase activities increased by 50% and 25%, respectively, while chloroplastic glycerate kinase and phosphoglycolate phosphatase increased by ~30%. The effect of MD was maximum in high light, indicating photo-oxidative stress was an influential factor to regulate photorespiration. Oxidative stress created in mitochondria caused a coordinative upregulation of photorespiration in other organelles. We provided evidence that reactive oxygen species are important signals for inter-organelle communication during photorespiration. Thus, MD can be a valuable tool to modulate the redox state in plant cells to study the metabolic consequences across membranes.

Chromium stress induced oxidative burst in Vigna mungo (L.) Hepper: physio-molecular and antioxidative enzymes regulation in cellular homeostasis

Vigna mungo (L.) Hepper commonly known as blackgram is an important legume crop with good quality dietary proteins and vitamins. Low production of blackgram in the chromium rich soil of Odisha is a serious concern against its demand. Chromium (VI) was tested on V. mungo var. B3-8-8 at 100, 150, 200, 250 and 300 µM concentration on growth, anti-oxidative enzymes and chromium content at 15, 30 and 45 d of treatments. Seed germination and growth decreased with increase dose and duration. Cr uptake induced oxidative burst with significant increase of osmolytes was observed in cell at lower doses but failed to adjust homeostasis at higher dose. Increase of GPX and SOD and decrease of CAT was observed as dose dependent. Increased protein content was detected in < 200 µM Cr concentration whereas, significant decrease of protein was noted thereafter. Down regulation of proteins (29.2 kDa and 32.6 kDa) was observed at > 250 µM of Cr. Total Cr uptake was greater in root than in shoot which might be due to poor translocation of heavy metal or detoxification. Thus, blackgram was able to maintain homeostasis at lower concentrations of Cr by activating the cascade of enzymes following cellular detoxification mechanism.

SUPPLEMENTARY INFORMATION

The online version of this article contains supplementary material available at (10.1007/s12298-021-00941-3).

Improved of growth and phytostabilization potential of lead (Pb) in Glebionis coronaria L. under the effect of IAA and GA3 alone and in combination with EDTA by altering biochemical attributes of stressed plants

This study evaluated the effect of EDTA, IAA and GA₃ alone and in combination in improving plant growth, Pb accumulation, and management of effective mechanisms associated with alleviation of Pb-induced adverse effect in Glebionis coronaria L. grown on industrial area in Alexandria. In this regards, 10-week-old plants were subjected to IAA and GA₃ as a foliar spray and EDTA was supplied in two doses 50 and 200mgkg^-1 soil. EDTA significantly reduced the plant growth and dry biomass, whereas GA₃ and IAA foliar spray increased growth significantly when compared with control (uncontaminated soil). In combined treatments of EDTA + GA₃ +IAA, the biomass was restored, which shows that GA₃ and IAA did compensate the negative effect of EDTA on plant growth and increased the Pb uptake significantly into roots. There were high GSH contents parallel with the increase of glutathione-S-transferase activity and induction of the antioxidant enzymes (SOD, CAT, APX, GR) as well as oxidized glutathione and ascorbic acid contents in leaves and roots when compared to control plants. This study suggests that G. coronaria is promising species for decontamination of Pb -contaminated soil and the application of EDTA together with IAA and GA₃ could be a useful strategy for enhancing the phytostabilization capability of Glebionis coronaria L. to eliminate Pb from contaminated soils. Novelty statement: The objective of this paper is to investigate the physiological performance of Glebionis coronaria as a new native for phytoremediation by phytostabilization mechanism of Pb after treatment with EDTA and phytohormones. Chemical additives of EDTA and GA₃ as well as IAA are promising alternatives to provide added benefits due to their individual credentials in improving the overall phytostabilization effectiveness and better immobilization efficiency in treating Pb contaminated soils by altering biochemical attributes of stressed plants. Currently these additives are not employed widely in large-scale field implementations, so field applications of these additives using Glebionis coronaria are essential for Phytoremediation of Pb-contaminated soils.

Foliar spray of Auxin/IAA modulates photosynthesis, elemental composition, ROS localization and antioxidant machinery to promote growth of Brassica juncea

Auxins (Aux) are primary growth regulators that regulate almost every aspect of growth and development in plants. It plays a vital role in various plant processes besides controlling the key aspects of cell division, cell expansion, and cell differentiation. Considering the significance of Aux, and its potential applications, a study was conducted to observe the impact of indole acetic acid (IAA), a most active and abundant form of Aux on Brassica juncea plants growing under natural environmental conditions. Different concentrations (0, 10^-10, 10^-8, 10^-6 M) of IAA were applied once in a day at 25-day stage of growth for 5 days, consecutively. Various parameters (growth, photosynthetic, biochemical, oxidative biomarkers and nutrient composition) were assessed at different days after sowing (DAS). Scanning electron microscopy (SEM) of leaf stomata, reactive oxygen species (ROS) localization in leaf and roots, and confocal microscopy were also conducted. The results revealed that all the IAA concentrations were effective in growth promotion and ROS reduction, however, the 10^-8 M of IAA exhibited the maximum improvement in all the above mentioned parameters as compared to the control.

Melatonin modulates photosynthesis, redox status, and elemental composition to promote growth of Brassica juncea-a dose-dependent effect

Melatonin (MEL) is an antioxidant molecule, present throughout plant kingdom, animals, and microbes. It is a well-known free radical scavenger and modulates growth and development in plants against various abiotic and biotic stresses. The present study was done to investigate the role of MEL as a foliar spray on the morphological, physiological, and biochemical parameters in Brassica juncea cv. Varuna. Five different doses (10, 20, 30, 40, or 50 μM) of MEL were applied as foliar spray to the leaf of plant at 25 days after sowing (DAS) and continued up to 30 DAS once in a day. The plants were sampled at 30, 45, and 60 DAS to assess various parameters. The present results indicate that most of the parameters, i.e., growth, photosynthetic, nutrients, and enzyme activities increased in a concentration dependent manner. MEL application reduced the accumulation of reactive oxygen species (ROS) by enhancing the antioxidant enzyme activities. Microscopic examinations further revealed a significant increase in the size of the stomatal aperture in the presence of MEL. Out of the various concentrations tested, 40 μM of MEL proved best and can be used for further studies.

The Pyruvate-Phosphate Dikinase (C4-SmPPDK) Gene From Suaeda monoica Enhances Photosynthesis, Carbon Assimilation, and Abiotic Stress Tolerance in a C3 Plant Under Elevated CO2 Conditions

A pyruvate-phosphate dikinase (C4-PPDK) gene was cloned from Suaeda monoica, which had a single-cell C4 photosynthesis pathway without Kranz anatomy and was functionally validated in a C3 model plant under different abiotic stress conditions in an ambient and elevated CO2 environment. Overexpression of SmPPDK promoted growth of C3 transgenic plants, enhancing their photosynthesis (CO2 assimilation) by lowering photorespiration under stress conditions. Transgenic plants also showed an improved physiological status, with higher relative water content (RWC), membrane integrity, concentration of glycine betaine, total soluble sugars, free amino acids, polyphenols and antioxidant activity, and lower electrolyte leakage, lipid peroxidation, free radical accumulation, and generation of reactive oxygen species (ROS), compared to control plants. Moreover, SmPPDK transgenic plants exhibited earlier flowering and higher dry biomass compared to controls. These results suggested that the C4-PPDK gene was appropriate for improvement of carbon assimilation, and it also played an important role in adaption to salinity and severe drought-induced stress. More intriguingly, an elevated CO2 environment alleviated the adverse effects of abiotic stress, particularly caused by drought through coordination of osmoprotectants and antioxidant defense systems. The molecular, physiological, metabolic, and biochemical indicators ameliorated the overall performance of model C3 plants overexpressing the C4-PPDK gene in an elevated CO2 environment, by lowering photorespiration metabolic processes, however, further studies are needed to confirm its precise role in C3 plants as protection against future climate change.

A CBL-interacting protein kinase AdCIPK5 confers salt and osmotic stress tolerance in transgenic tobacco

CBL interacting protein kinases play important roles in adaptation to stress conditions. In the present study, we isolated a CBL-interacting protein kinase homolog (AdCIPK5) from a wild peanut (Arachis diogoi) with similarity to AtCIPK5 of Arabidopsis. Expression analyses in leaves of the wild peanut showed AdCIPK5 induction by exogenous signaling molecules including salicylic acid, abscisic acid and ethylene or abiotic stress factors like salt, PEG and sorbitol. The recombinant AdCIPK5-GFP protein was found to be localized to the nucleus, plasma membrane and cytoplasm. We overexpressed AdCIPK5 in tobacco plants and checked their level of tolerance to biotic and abiotic stresses. While wild type and transgenic plants displayed no significant differences to the treatment with the phytopathogen, Phytophthora parasitica pv nicotianae, the expression of AdCIPK5 increased salt and osmotic tolerance in transgenic plants. Analysis of different physiological parameters revealed that the transgenic plants maintained higher chlorophyll content and catalase activity with lower levels of H2O2 and MDA content during the abiotic stress conditions. AdCIPK5 overexpression also contributed to the maintenance of a higher the K+/Na+ ratio under salt stress. The enhanced tolerance of transgenic plants was associated with elevated expression of stress-related marker genes; NtERD10C, NtERD10D, NtNCED1, NtSus1, NtCAT and NtSOS1. Taken together, these results indicate that AdCIPK5 is a positive regulator of salt and osmotic stress tolerance.

Proteomic and physiological responses in mangrove Kandelia candel roots under short-term high-salinity stress

Kandelia candel is one of the mangrove species that are most resistant to environmental stress. As a typical nonsalt-secreting mangrove plant, K. candel is an ideal biological material to analyze the molecular mechanism of salt tolerance in woody plants. In this study, changes in protein abundance and expression profile in K. candel roots under high-salinity stress of 600 mmol L^-1 NaCl were analyzed using isobaric tags for relative and absolute quantification (iTRAQ) assay. Moreover, the physiological parameters associated with metabolic pathways in which the differentially abundant proteins (DAPs) are involved were determined. A total of 5577 proteins were identified by iTRAQ analysis of the K. candel root proteins, of which 227 were DAPs with a fold change ratio >1.2 or a fold change ratio <0.83 and a P-value <0.05. A total of 227 DAPs consisting of 110 up-regulated and 117 down-regulated proteins were identified. Our Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the DAPs were primarily involved in biological processes including carbohydrate and energy metabolisms, stress response and defense, cell wall structure, and secondary metabolism. The results of the physiological parameters showed that their profile changes were consistent with those of the proteome analysis. The results of the proteome and physiological parameters showed that K. candel roots could resist high-salinity stress by maintaining a normal Embden-Meyerhof-Parnas and tricarboxylic acid (EMP-TCA) pathway, increasing the activities of various antioxidant enzymes and antioxidant contents, stabilizing the cell wall structure, and accumulating secondary metabolites such as triterpenoids.

Lead accumulation and distribution in maize seedlings: Relevance to biomass production and metal phytoextraction

Among trace metals, lead is a highly toxic contaminant, being hazardous to humans and animals. Application of maize plants for phytoremediation of polluted soils and waters has recently been of particular interest. The aim of this work is to investigate the Pb-phytoextraction potential of the maize cv. Tzariza used widely in Eastern European agriculture. Maize seedlings were exposed in a nutrient solution to 1-10000 µM of Pb²⁺ for 21 days. Lead accumulated mostly in conductive tissues and shoots at 0.1 mM and higher concentrations of Pb in growth medium. Pb at concentrations of 1 and 10 mM caused an increase in the superoxide anion level and the catalase activity in maize leaves. Lead ions were tolerable to maize seedlings within a concentration range up to 1000 µM of Pb^2+. The levels of lead in the nutrient solution above 1 mM resulted in inhibition of the growth of axial organs, decrease in leaf area, inhibition of water absorption, and reduction in accumulation of biomass. Theoretical considerations indicate that in the temperate climates of the phytoremediation with maize may allow annual removal up to 90 kg of Pb per km², depending on the initial level of soil contamination.

Overexpression of SbSI-1, A Nuclear Protein from Salicornia brachiata Confers Drought and Salt Stress Tolerance and Maintains Photosynthetic Efficiency in Transgenic Tobacco

A novel Salicornia brachiata Salt Inducible (SbSI-1) gene was isolated and overexpressed in tobacco for in planta functional validation subjected to drought and salt stress. SbSI-1 is a nuclear protein. The transgenic tobacco overexpressing SbSI-1 gene exhibited better seed germination, growth performances, pigment contents, cell viability, starch accumulation, and tolerance index under drought and salt stress. Overexpression of SbSI-1 gene alleviated the build-up of reactive oxygen species (ROS) and curtailed the ROS-induced oxidative damages thus improved the physiological health of transgenic tobacco under stressed conditions. The higher activities of antioxidant enzymes, lower accumulation of ROS, higher membrane stability, relative water content, and polyphenol contents indicated the better survival of the transgenic tobacco than wild-type (WT) tobacco under stressed conditions. Transgenic tobacco had a higher net photosynthetic rate, PSII operating efficiency, and performance index under drought and salt stress. Higher accumulation of compatible solutes and K⁺/Na⁺ ratio in transgenic tobacco than WT showed the better osmotic and redox homeostasis under stressed conditions. The up-regulation of genes encoding antioxidant enzymes (NtSOD, NtAPX, and NtCAT) and transcription factors (NtDREB2 and NtAP2) in transgenic tobacco under stressed conditions showed the role of SbSI-1 in ROS alleviation and involvement of this gene in abiotic stress tolerance. Multivariate data analysis exhibited statistical distinction among growth responses, physiological health, osmotic adjustment, and photosynthetic responses of WT and transgenic tobacco under stressed conditions. The overexpression of SbSI-1 gene curtailed the ROS-induced oxidative damages and maintained the osmotic homeostasis under stress conditions thus improved physiological health and photosynthetic efficiencies of the transgenic tobacco overexpressing SbSI-1 gene.

Stomatal behaviors reflect enantioselective phytotoxicity of chiral herbicide dichlorprop in Arabidopsis thaliana

Stomata in plants play vital roles in water transpiration and gas exchange necessary for photosynthesis, which are critical for the plants growth. Until now, however, the effect of chiral herbicides on the response of stomata was poorly understood. To unveil this puzzle, the enantioselective effect of chiral herbicide dichloroprop (DCPP) on stomata in Arabidopsis thaliana was investigated. It was found that (R)-DCPP preferentially promoted the extent of stomatal opening in Arabidopsis leaves, resulting in 59.84% enhancement at 0.3μmol·L(-1) comparing to the control, where (S)- and (Rac)-DCPP exhibited no significant differences. Enantioselectivity was also observed in the response of stomata to DCPP. To better understand the mechanism involved, the reactive oxygen species (ROS) production and antioxidant system defense were measured. Interestingly, the ROS production in Arabidopsis leaves was also enantioselective. The (R)-DCPP treatments resulted in 6.08-fold enhancement compared with the control, whereas 1.35- and 2.51-fold increases occurred in (S)-DCPP and (Rac)-DCPP treatments, respectively. The promoting of stomatal opening was positively correlated with ROS production. In addition, the antioxidant system response provided evidence of oxidative stress and damage caused by DCPP. This study confirmed that the ROS produced by DCPP promoted stomatal opening and suggested a potential sight to elucidate the phytotoxicity of chiral herbicides.

Alternative Oxidase Pathway Optimizes Photosynthesis During Osmotic and Temperature Stress by Regulating Cellular ROS, Malate Valve and Antioxidative Systems

The present study reveals the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under osmotic and temperature stress conditions in the mesophyll protoplasts of Pisum sativum. The responses of photosynthesis and respiration were monitored at saturating light intensity of 1000 μmoles m(-2) s(-1) at 25°C under a range of sorbitol concentrations from 0.4 to 1.0 M to induce hyper-osmotic stress and by varying the temperature of the thermo-jacketed pre-incubation chamber from 25 to 10°C to impose sub-optimal temperature stress. Compared to controls (0.4 M sorbitol and 25°C), the mesophyll protoplasts showed remarkable decrease in NaHCO3-dependent O2 evolution (indicator of photosynthetic carbon assimilation), under both hyper-osmotic (1.0 M sorbitol) and sub-optimal temperature stress conditions (10°C), while the decrease in rates of respiratory O2 uptake were marginal. The capacity of AOX pathway increased significantly in parallel to increase in intracellular pyruvate and reactive oxygen species (ROS) levels under both hyper-osmotic stress and sub-optimal temperature stress under the background of saturating light. The ratio of redox couple (Malate/OAA) related to malate valve increased in contrast to the ratio of redox couple (GSH/GSSG) related to antioxidative system during hyper-osmotic stress. Further, the ratio of GSH/GSSG decreased in the presence of sub-optimal temperature, while the ratio of Malate/OAA showed no visible changes. Also, the redox ratios of pyridine nucleotides increased under hyper-osmotic (NADH/NAD) and sub-optimal temperature (NADPH/NADP) stresses, respectively. However, upon restriction of AOX pathway by using salicylhydroxamic acid (SHAM), the observed changes in NaHCO3-dependent O2 evolution, cellular ROS, redox ratios of Malate/OAA, NAD(P)H/NAD(P) and GSH/GSSG were further aggravated under stress conditions with concomitant modulations in NADP-MDH and antioxidant enzymes. Taken together, the results indicated the importance of AOX pathway in optimizing photosynthesis under both hyper-osmotic stress and sub-optimal temperatures. Regulation of ROS through redox couples related to malate valve and antioxidant system by AOX pathway to optimize photosynthesis under these stresses are discussed.

Molecular and Physiological Mechanisms of Heavy Metal Tolerance in Atriplex halimus

A study was carried out to identify the mechanisms underlying stress caused by Cd and Pb accumulation in leaves of Atriplex halimus L. collected from habitats representing different kinds of pollution. Mean concentrations of Cd and Pb in aerial parts exceeded the critical levels in polluted plants as compared to reference plants. There were significant reduction in guiacol peroxidase, ascorbate peroxidase and glutathione content in most of polluted plants. The results showed increase in superoxide dismutase enzyme in all polluted plants. The significant increment in catalase enzyme, glutathione S-transeferase and ascorbic acid content were observed in most of polluted plants. Results of the nine differential expressed bands showed down regulation of NADH dehydrogenase and Sedoheptulose-bisphosphatase in polluted plants. In contrast, there were six regulated genes in highly polluted plants, representing transcription factors, membrane transporters and ROS detoxification. The transcription level of phytochelatin synthase showed a significant increase in all polluted plants, while heavy metal ATPase transporter expression significantly increased in some polluted plants. In conclusion, A. halimus may use two different strategies against Cd and Pb stress, in which the molecular and physiological features affords similar levels of Cd and Pb tolerance through binding, sequestration and the reduction of harmful effect of heavy metals.

High light acclimation of Oryza sativa L. leaves involves specific photosynthetic-sourced changes of NADPH/NADP⁺ in the midvein

Previous studies have shown that exposure of Arabidopsis leaves to high light (HL) causes a systemic acquired acclimation (SAA) response in the vasculature. It has been postulated that C₄-like photosynthesis in the leaf veins triggers this response via the Mehler reaction. To investigate this proposed connection and extend SAA to other plants, we examined the redox state of NADPH, ascorbate (ASA), and glutathione (GSH) pools; levels and histochemical localization of O₂- and H₂O₂ signals; and activities of antioxidant enzymes in the midvein and leaf lamina of rice, when they were subjected to HL and low light. The results showed that (1) high NADPH/NADP(+) was generated by C₄-like photosynthesis under HL in the midvein and (2) SAA was colocally induced by HL, as indicated by the combined signaling network, including the decrease in redox status of ASA and GSH pools, accumulation of H₂O₂ and O₂- signals, and high superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. The high correlations between these occurrences suggest that the enhanced NADPH/NADP(+) in HL-treated midveins might alter redox status of ASA and GSH pools and trigger H₂O₂ and O₂- signals during SAA via the Mehler reaction. These changes in turn upregulate SOD and APX activities in the midvein. In conclusion, SAA may be a common regulatory mechanism for the adaptation of angiosperms to HL. Manipulation of NADPH/NADP(+) levels by C₄-like photosynthesis promotes SAA under HL stress in the midvein.

Exogenous trehalose largely alleviates ionic unbalance, ROS burst, and PCD occurrence induced by high salinity in Arabidopsis seedlings

Trehalose (Tre) has been reported to play a critical role in plant response to salinity and the involved mechanisms remain to be investigated in detail. Here, the putative roles of Tre in regulation of ionic balance, cellular redox state, cell death were studied in Arabidopsis under high salt condition. Our results found that the salt-induced restrictions on both vegetative and reproductive growth in salt-stressed plants were largely alleviated by exogenous supply with Tre. The microprobe analysis of ionic dynamics in the leaf and stem of florescence highlighted the Tre ability to retain K and K/Na ratio in plant tissues to improve salt tolerance. The flow cytometry assay of cellular levels of reactive oxygen species and programmed cell death displayed that Tre was able to antagonized salt-induced damages in redox state and cell death and sucrose did not play the same role with Tre. By comparing ionic distribution in leaf and inflorescence stem (IS), we found that Tre was able to restrict Na transportation to IS from leaves since that the ratio of Na accumulation in leaves relative to IS was largely improved due to Tre. The marked decrease of Na ion and improved sucrose level in IS might account for the promoted floral growth when Tre was included in the saline solution. At the same time, endogenous soluble sugars and antioxidant enzyme activities in the salt-stressed plants were also elevated by Tre to counteract high salt stress. We concluded that Tre could improve Arabidopsis salt resistance with respect to biomass accumulation and floral transition in the means of regulating plant redox state, cell death, and ionic distribution.

Effect of nitric oxide signaling in bacterial-treated soybean plant under salt stress

To understand protective roles of nitric oxide against salt stress, the effects of exogenous sodium nitroprusside on activities of lipoxygenase, peroxidase, phenylalanine ammonialyase, catalase, superoxide dismutase enzymes, proline accumulation, and distribution of sodium in soybean plants under salt were determined. Application of sodium nitroprusside + bacterium enhanced plant growth-promotion characteristics, activities of different enzymes, and proline accumulation in the presence of sodium nitroprusside under salt stress. Treatment with NaCl at 200 mM and sodium nitroprusside (0.1 mM) reduced Na⁺ levels but increased K⁺ levels in leaves in comparison with the NaCl-treated plants. Correspondingly, the plants treated with exogenous sodium nitroprusside and NaCl maintained a lower ratio of [Na⁺]/[K⁺] in NaCl-stressed plants.

Salt and genotype impact on antioxidative enzymes and lipid peroxidation in two rice cultivars during de-etiolation

Crop yield is severely affected by soil salinity, as salt levels that are harmful to plant growth occur in large terrestrial areas of the world. The present investigation describes the studies of enzymatic activities, in-gel assays, gene expression of some of the major antioxidative enzymes, tocopherol accumulation, lipid peroxidation, ascorbate and dehydroascorbate contents in a salt-sensitive rice genotype PB1, and a relatively salt-tolerant cultivar CSR10 in response to 200 mM NaCl. Salt solution was added to the roots of hydroponically grown 5-day-old etiolated rice seedlings, 12 h prior to transfer to cool white fluorescent + incandescent light (100 μmol photons m(-2) s(-1)). Total tocopherol and ascorbate contents declined in salt-stressed rice seedlings. Among antioxidative enzymes, an increase in the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11), glutathione reductase (EC 1.6.4.2), and their gene expression was observed in both cultivars in response to salt stress. The salt-tolerant cultivar CSR10 resisted stress due to its early preparedness to combat oxidative stress via upregulation of gene expression and enzymatic activities of antioxidative enzymes and a higher redox status of the antioxidant ascorbate even in a non-stressed environment.

Importance of ROS and antioxidant system during the beneficial interactions of mitochondrial metabolism with photosynthetic carbon assimilation

The present study suggests the importance of reactive oxygen species (ROS) and antioxidant metabolites as biochemical signals during the beneficial interactions of mitochondrial metabolism with photosynthetic carbon assimilation at saturating light and optimal CO2. Changes in steady-state photosynthesis of pea mesophyll protoplasts monitored in the presence of antimycin A [AA, inhibitor of cytochrome oxidase (COX) pathway] and salicylhydroxamic acid [SHAM, inhibitor of alternative oxidase (AOX) pathway] were correlated with total cellular ROS and its scavenging system. Along with superoxide dismutase (SOD) and catalase (CAT), responses of enzymatic components--ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), glutathione reductase (GR) and non-enzymatic redox components of ascorbate-glutathione (Asc-GSH) cycle, which play a significant role in scavenging cellular ROS, were examined in the presence of mitochondrial inhibitors. Both AA and SHAM caused marked reduction in photosynthetic carbon assimilation with concomitant rise in total cellular ROS. Restriction of electron transport through COX or AOX pathway had differential effect on ROS generating (SOD), ROS scavenging (CAT and APX) and antioxidant (Asc and GSH) regenerating (MDAR and GR) enzymes. Further, restriction of mitochondrial electron transport decreased redox ratios of both Asc and GSH. However, while decrease in redox ratio of Asc was more prominent in the presence of SHAM in light compared with dark, decrease in redox ratio of GSH was similar in both dark and light. These results suggest that the maintenance of cellular ROS at optimal levels is a prerequisite to sustain high photosynthetic rates which in turn is regulated by respiratory capacities of COX and AOX pathways.

Novel mechanism of modulating natural antioxidants in functional foods: involvement of plant growth promoting Rhizobacteria NRRL B-30488

The significance of plant growth-promoting rhizobacteria (PGPR) mediated increase in antioxidant potential in vegetables is yet unknown. The plant growth-promoting bacterium Bacillus lentimorbus NRRL B-30488 (B-30488) mediated induction of dietary antioxidant in vegetables ( Trigonella foenum-graecum, Lactuca sativa, Spinacia oleracea, and Daucus carota) and fruit ( Citrus sinensis) after minimal processing (fresh, boiled, and frozen) was tested by estimating the total phenol content, level of antioxidant enzymes, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide scavenging activities along with integral radical scavenging capacity by photochemiluminescence assay and inhibition of lipid peroxidation. Minimal processing of vegetables showed that T. foenum-graecum had the highest phenol content in B-30488-treated plants followed by L. sativa, D. carota, and S. oleracea. Thermally treated vegetables T. foenum-graecum (26-114.5 GAE microg mg (-1)) had an exceptionally high total phenolic content, followed by D. carota (25.27-101.32 GAE microg mg (-1)), L. sativa (23.22-101.10 GAE microg mg (-1)), and S. oleracea (21.87-87.57 GAE microg mg (-1)). Among the vegetables and fruit used in this study for enzymatic estimation, induction of antioxidant enzymes, namely, polyphenol oxidase (PPO), ascorbate peroxidase (APX), catalase (CAT), and superoxidase dismutase (SOD), was observed in edible parts of T. foenum-graecum, L. sativa, S. oleracea, and D. carota, after inoculation with B-30488. The scavenging capacity of the vegetables treated with B-30488 against DPPH and superoxide anion radical activity was found to be significantly high as compared to nontreated control. Mild food processing had no adverse effect on radical scavenging capacity. Photochemiluminescence also ascertains the above findings. The ability of the plant extracts to protect against lipid peroxidation and its ability to prevent oxidation of reduced glutathione (GSH) was measured in rat liver homogenate, and the results suggested that the inoculated plant exhibited better activity in all of the screened plants. Significant increases in shoot length, root length, and dry weight, averaging 164, 132, and 135% in T. foenum-graecum, 174, 141, and 156% in L. sativa, 129, 141, and 59%, in S. oleracea, and 125, 146, and 42% in D. carota, respectively, over untreated controls, were attained in greenhouse trials. To the best of the authors' knowledge, this is the first report of PGPR-mediated induction of antioxidant enzyme activity (PPO, APX, CAT, and SOD) along with the antioxidant activity of the extracts in both in vitro (DPPH radical scavenging and superoxide scavenging) and ex vivo conditions using the rat liver tissue (percent inhibition of lipid peroxidation and prevention of oxidation of GSH) and phenolic content. The results demonstrate the PGPR-mediated induction of antioxidant level in vegetables and fruit controls oxidative damage even after minimal processing and thus is indicative of its potential as a viable substitute of synthetic antioxidants.

Engineering of ubiquinone biosynthesis using the yeast coq2 gene confers oxidative stress tolerance in transgenic tobacco

Ubiquinone (UQ), an electron carrier in the respiratory chain ranging from bacteria to humans, shows antioxidative activity in vitro, but its physiological role in vivo is not yet clarified in plants. UQ biosynthesis was modified by overexpressing the yeast gene coq2, which encodes p-hydroxybenzoate:polyprenyltransferase, to increase the accumulation of UQ-6 in yeast and UQ-10 in tobacco. The yeast and tobacco transgenic lines showed about a three- and six-fold increase in UQ, respectively. COQ2 polypeptide, the localization of which was forcibly altered to the endoplasmic reticulum, had the same or a greater effect as mitochondria-localized COQ2 on the increase in UQ in both the yeast and tobacco transformants, indicating that the UQ intermediate is transported from the endoplasmic reticulum to the mitochondria. Plants with a high UQ level are more resistant to oxidative stresses caused by methyl viologen or high salinity. This is attributable to the greater radical scavenging ability of the transgenic lines when compared with the wild type.

Defense potentials to NaCl in a mangrove, Bruguiera parviflora: differential changes of isoforms of some antioxidative enzymes

In order to assess the role of the antioxidative defense system against salt treatment, the activities of some antioxidative enzymes and levels of antioxidants were monitored in a true mangrove, Bruguiera parviflora, subjected to varying levels of NaCl under hydroponic culture. In the leaves of B. parviflora, salt treatment preferentially enhanced the content of H2O2 as well as the activity of ascorbate peroxidase (APX), guaiacol peroxidase (GPX), glutathione reductase (GR), and superoxide dismutase (SOD), whereas it induced the decrease of total ascorbate and glutathione (GSH+GSSG) content as well as catalase (CAT) activity. Analysis of isoforms of antioxidative enzymes by native PAGE and activity staining revealed that leaves of B. parviflora had one isoform each of Mn-SOD and Cu/Zn-SOD and three isoforms of Fe-SOD. Expression of Mn-SOD and Fe-SOD-2 was preferentially elevated by NaCl. Similarly, out of the six isoforms of GPX, the GPX-1, 2, 3 and 6 were enhanced by salt treatment but the levels of GPX-4 and -5 changed minimally as compared to those of a control. Activity staining gel revealed only one prominent isoform of APX and two isoforms of GR (GR-1 and GR-2), all of these isoforms increased upon salt exposure. Four CAT-isoforms were identified, among which the prominent CAT-2 isoform level was maximally reduced, suggesting differential down regulation of CAT isoforms by NaCl. The concentrations of malondialdehyde (MDA), a product of lipid peroxidation, remained unchanged in leaves of the plant treated with different concentrations of NaCl. This suggests that plants are protected against activated oxygen species by the elevated levels of certain antioxidative enzymes, thus avoiding lipid peroxidation during salt exposure. The differential changes in the levels of the isoforms due to NaCl treatment may be useful as markers for recognizing salt tolerance in mangroves.

Molecular cloning, characterization and expression analysis of two catalase isozyme genes in barley

Clones representing two distinct barley catalase genes, Cat1 and Cat2, were found in a cDNA library prepared from seedling polysomal mRNA. Both clones were sequenced, and their deduced amino acid sequences were found to have high homology with maize and rice catalase genes. Cat1 had a 91% deduced amino acid sequence identity to CAT-1 of maize and 92% to CAT B of rice. Cat2 had 72 and 79% amino acid sequence identities to maize CAT-2 and -3 and 89% to CAT A of rice. Barley, maize or rice isozymes could be divided into two distinct groups by amino acid homologies, with one group homologous to the mitochondria-associated CAT-3 of maize and the other homologous to the maize peroxisomal/glyoxysomal CAT-1. Both barley CATs contained possible peroxisomal targeting signals, but neither had favorable mitochondrial targeting sequences. Cat1 mRNA occurred in whole endosperms (aleurones plus starchy endosperm), in isolated aleurones and in developing seeds, but Cat2 mRNA was virtually absent. Both mRNAs displayed different developmental expression patterns in scutella of germinating seeds. Cat2 mRNA predominated in etiolated seedling shoots and leaf blades. Barley genomic DNA contained two genes for Cat1 and one gene for Cat2. The Cat2 gene was mapped to the long arm of chromosome 4, 2.9 cM in telomeric orientation from the mlo locus conferring resistance to the powdery mildew fungus (Erysiphe graminis f.sp. hordei).

Chilling-enhanced photooxidation: The production, action and study of reactive oxygen species produced during chilling in the light

Chilling-enhanced photooxidation is the light- and oxygen-dependent bleaching of photosynthetic pigments that occurs upon the exposure of chilling-sensitive plants to temperatures below approximately 10 °C. The oxidants responsible for the bleaching are the reactive oxygen species (ROS) singlet oxygen ((1)O2), superoxide anion radical (O 2 (∸) ,hydrogen peroxide (H2O2), the hydroxyl radical (OH·), and the monodehydroascorbate radical (MDA) which are generated by a leakage of absorbed light energy from the photosynthetic electron transport chain. Cold temperatures slow the energy-consuming Calvin-Benson Cycle enzymes more than the energy-transducing light reactions, thus causing leakage of energy to oxygen. ROS and MDA are removed, in part, by the action of antioxidant enzymes of the Halliwell/Foyer/Asada Cycle. Chloroplasts also contain high levels of both lipid- and water-soluble antioxidants that act alone or in concert with the HFA Cycle enzymes to scavenge ROS. The ability of chilling-resistant plants to maintain active HFA Cycle enzymes and adequate levels of antioxidants in the cold and light contributes to their ability to resist chilling-enhanced photooxidation. The absence of this ability in chilling-sensitive species makes them susceptible to chilling-enhanced photooxidation. Chloroplasts may reduce the generation of ROS by dissipating the absorbed energy through a number of quenching mechanisms involving zeaxanthin formation, state changes and the increased usage of reducing equivalents by other anabolic pathways found in the stroma. During chilling in the light, ROS produced in chilling-sensitive plants lower the redox potential of the chloroplast stroma to such a degree that reductively-activated regulatory enzymes of the Calvin Cycle, sedohepulose 1,7 bisphosphatase (EC 3.1.3.37) and fructose 1,6 bisphosphatase (EC 3.1.3.11), are oxidatively inhibited. This inhibition is reversible in vitro with a DTT treatment indicating that the enzymes themselves are not permanently damaged. The inhibition of SBPase and FBPase may fully explain the inhibition in whole leaf gas exchange seen upon the rewarming of chilling-sensitive plants chilled in the light. Methods for the study of ROS in chilling-enhanced photooxidation and challenges for the future are discussed.

Catalatic capacities in heat-shocked Euglena cells

1. Various heat treatments were applied to the wild strain Z. Klebs. of Euglena gracilis. 2. Samples of cells were taken at day 1 of the culture at 26 degrees C in a 33 mM lactate medium, when the catalatic capacities of the catalase were highest. 3. They were either submitted to heat treatments (36 and 38 degrees C), or heat-shocks (40, 42 degrees C) or non-permissive heat stress (45 degrees C) for 15 min, 1 and 2 hr. 4. After a 2-hr 45 degrees C treatment the cells were unable to recover normal physiological functions. 5. Heat treatments between 36 and 38 degrees C decreased the catalatic capacities of cells, while heat-shocks at 40 and 42 degrees C strongly reinforced these capacities of hydrogen peroxide dismutation. 6. Having been heat-shocked at 42 degrees C for 2 hr, the cells became different from control cells: (a) after several months of culture, they displayed catalatic capacities increased by 65%; (b) they were able from now on to survive a 2 hr heat shock at 45 degrees C.

Changes in the Activity of Catalase (EC 1.11.1.6) in Relation to the Dormancy of Grapevine (Vitis vinifera L.) Buds

Catalase activity in grapevine (Vitis vinifera L.) buds cv. ;Perlette.' increased to a maximum in October and thereafter decreased within 3 months to less than half its maximal rate. The decrease in catalase activity coincided with the decline in temperature during winter. The rate of sprouting of buds forced at 23 degrees C was negatively related to the activity of catalase. Artificial chilling of grapevine canes at 5 degrees C resulted in a 25% decrease of catalase activity in the buds after 3 days and 31% after 17 days. The activity of catalase increased to the control level only 96 hours after removing canes from 5 degrees C to room temperature. Efficient buddormancy breaking agents, such as thiourea and cyanamide decreased catalase activity to 64 and 50% of the controls respectively, while the activity of peroxidase remained the same under those conditions. A less efficient dormancy breaking agent dinitro-ortho-cresol, did not decrease catalase activity.