Auxin autotrophic tobacco callus tissues resist oxidative stress: the importance of glutathione S-transferase and glutathione peroxidase activities in auxin heterotrophic and autotrophic calli

Assessment of the Molecular Responses of an Ancient Angiosperm against Atypical Insect Oviposition: The Case of Hass Avocados and the Tephritid Fly Anastrepha ludens

Anastrepha spp. (Diptera: Tephritidae) infestations cause significant economic losses in commercial fruit production worldwide. However, some plants quickly counteract the insertion of eggs by females by generating neoplasia and hindering eclosion, as is the case for Persea americana Mill., cv. Hass (Hass avocados). We followed a combined transcriptomics/metabolomics approach to identify the molecular mechanisms triggered by Hass avocados to detect and react to the oviposition of the pestiferous Anastrepha ludens (Loew). We evaluated two conditions: fruit damaged using a sterile pin (pin) and fruit oviposited by A. ludens females (ovi). We evaluated both of the conditions in a time course experiment covering five sampling points: without treatment (day 0), 20 min after the treatment (day 1), and days 3, 6, and 9 after the treatment. We identified 288 differentially expressed genes related to the treatments. Oviposition (and possibly bacteria on the eggs' surface) induces a plant hypersensitive response (HR), triggering a chitin receptor, producing an oxidative burst, and synthesizing phytoalexins. We also observed a process of cell wall modification and polyphenols biosynthesis, which could lead to polymerization in the neoplastic tissue surrounding the eggs.

Role of Jasmonates, Calcium, and Glutathione in Plants to Combat Abiotic Stresses Through Precise Signaling Cascade

Plant growth regulators have an important role in various developmental processes during the life cycle of plants. They are involved in abiotic stress responses and tolerance. They have very well-developed capabilities to sense the changes in their external milieu and initiate an appropriate signaling cascade that leads to the activation of plant defense mechanisms. The plant defense system activation causes build-up of plant defense hormones like jasmonic acid (JA) and antioxidant systems like glutathione (GSH). Moreover, calcium (Ca2+) transients are also seen during abiotic stress conditions depicting the role of Ca2+ in alleviating abiotic stress as well. Therefore, these growth regulators tend to control plant growth under varying abiotic stresses by regulating its oxidative defense and detoxification system. This review highlights the role of Jasmonates, Calcium, and glutathione in abiotic stress tolerance and activation of possible novel interlinked signaling cascade between them. Further, phyto-hormone crosstalk with jasmonates, calcium and glutathione under abiotic stress conditions followed by brief insights on omics approaches is also elucidated.

Genome-wide identification of the glutathione transferase superfamily in the model organism Brachypodium distachyon

The detoxification of harmful metabolites can determine the effectiveness of plant stress responses. Scavenging some of these toxic stress by-products through the reduced form of glutathione is catalysed by members of the glutathione transferase (GST) enzyme superfamily. The involvement of these enzymes was studied in the model organism Brachypodium distachyon (L.)P.Beauv. Bd21 and in its derivative Bd21-3, a more drought tolerant line. Osmotic stress treatment resulted in a decrease in the water potential of both Brachypodium genotypes, the difference between the control and treated plant's ψw decreased by the last sampling day in Bd21-3, suggesting some degree of adaptation to the applied osmotic stress. Increased GST activity revealed a severe defence reaction against the harmful imbalance of the redox environment. Screening for the gene sequences led to the identification of 91 full-length or partial GST sequences. Although purple false brome has a relatively small genome, the number of identified GST genes was almost as high as the number predicted in wheat. The estimation of GST expression showed stress-induced differences: higher expression levels or the fast induction of BdGSTF8, BdGSTU35 and BdGSTU42 gene products presumably indicate a strong detoxification under osmotic stress.

Biochemical response of hybrid black poplar tissue culture (Populus × canadensis) on water stress

In this study, poplar tissue culture (hybrid black poplar, M1 genotype) was subjected to water stress influenced by polyethyleneglycol 6000 (100 and 200 mOsm PEG 6000). The aim of the research was to investigate the biochemical response of poplar tissue culture on water deficit regime. Antioxidant status was analyzed including antioxidant enzymes, superoxide-dismutase (SOD), catalase (CAT), guiacol-peroxidase (GPx), glutathione-peroxidase (GSH-Px), glutathione-reductase, reduced glutathione, total phenol content, Ferric reducing antioxidant power and DPPH radical antioxidant power. Polyphenol oxidase and phenylalanine-ammonium-lyase were determined as enzymatic markers of polyphenol metabolism. Among oxidative stress parameters lipid peroxidation, carbonyl-proteins, hydrogen-peroxide, reactive oxygen species, nitric-oxide and peroxynitrite were determined. Proline, proline-dehydrogenase and glycinebetaine were measured also as parameters of water stress. Cell viability is finally determined as a biological indicator of osmotic stress. It was found that water stress induced reactive oxygen and nitrogen species and lipid peroxidation in leaves of hybrid black poplar and reduced cell viability. Antioxidant enzymes including SOD, GPx, CAT and GSH-Px were induced but total phenol content and antioxidant capacity were reduced by PEG 6000 mediated osmotic stress. The highest biochemical response and adaptive reaction was the increase of proline and GB especially by 200 mOsm PEG. While long term molecular analysis will be necessary to fully address the poplar potentials for water stress adaptation, our results on hybrid black poplar suggest that glycine-betaine, proline and PDH enzyme might be the most important markers of poplar on water stress and that future efforts should be focused on these markers and strategies to enhance their concentration in poplar.

Glutathione in plants: biosynthesis and physiological role in environmental stress tolerance

Glutathione (GSH; γ-glutamyl-cysteinyl-glycine) is a small intracellular thiol molecule which is considered as a strong non-enzymatic antioxidant. Glutathione regulates multiple metabolic functions; for example, it protects membranes by maintaining the reduced state of both α-tocopherol and zeaxanthin, it prevents the oxidative denaturation of proteins under stress conditions by protecting their thiol groups, and it serves as a substrate for both glutathione peroxidase and glutathione S-transferase. By acting as a precursor of phytochelatins, GSH helps in the chelating of toxic metals/metalloids which are then transported and sequestered in the vacuole. The glyoxalase pathway (consisting of glyoxalase I and glyoxalase II enzymes) for detoxification of methylglyoxal, a cytotoxic molecule, also requires GSH in the first reaction step. For these reasons, much attention has recently been directed to elucidation of the role of this molecule in conferring tolerance to abiotic stress. Recently, this molecule has drawn much attention because of its interaction with other signaling molecules and phytohormones. In this review, we have discussed the recent progress in GSH biosynthesis, metabolism and its role in abiotic stress tolerance.

Physiological and molecular responses to heavy metal stresses suggest different detoxification mechanism of Populus deltoides and P. x canadensis

Plants have divergent defense mechanisms against the harmful effects of heavy metals present in excess in soils and groundwaters. Poplars (Populus spp.) are widely cultivated because of their rapid growth and high biomass production, and members of the genus are increasingly used as experimental model organisms of trees and for phytoremediation purposes. Our aim was to investigate the copper and zinc stress responses of three outstanding biomass producer bred poplar lines to identify such transcripts of genes involved in the detoxification mechanisms, which can play an important role in the protection against heavy metals. Poplar cuttings were grown hydroponically and subjected to short-term (one week) mild and sublethal copper and zinc stresses. We evaluated the effects of the applied heavy metals and the responses of plants by detecting the changes of multiple physiological and biochemical parameters. The most severe cellular oxidative damage was caused by 30μM copper treatment, while zinc was less harmful. Analysis of stress-related transcripts revealed genotype-specific differences that are likely related to alterations in heavy metal tolerance. P. deltoides clones B-229 and PE 19/66 clones were clearly more effective at inducing the expression of various genes implicated in the detoxification process, such as the glutathione transferases, metallothioneins, ABC transporters, (namely PtGSTU51, PxMT1, PdABCC2,3), while the P. canadensis line M-1 accumulated more metal, resulting in greater cellular oxidative damage. Our results show that all three poplar clones are efficient in stress acclimatization, but with different molecular bases.

Bio indices for 2,4-D sensitivity between two plant species: Azolla pinnata R.Br. and Vernonia cinerea L. with their cellular responses

In the present experiment a pteridophytic species Azolla and an angiospermic species Vernonia were evaluated on the basis of cellular reactivity for herbicidal action through ongoing concentrations. Initially, both the species recorded a significant activity of IAA-oxidase as mark of IAA metabolism with herbicidal sensitivity. Still, Vernonia species were more affected on 2,4-D mediated auxin catabolism. The loss of auxin concentrations on the tissues by 2,4-D reaction was also reflected on growth parameters including relative growth rate and chlorophyll biosynthesis. In a dose dependent manner Vernonia plants were more affected with loss of chlorophyll content and decline in relative growth rate. On the other hand, both those parameters were adjusted significantly with 2,4-D accumulation in Azolla. The stability of cellular metabolism was documented by significant down regulation of protein and lipid peroxidation with concomitant moderation to superoxide and hydrogen peroxide accumulation. The later two were more vulnerable to damage in the Vernonia plant with profuse accumulation of protein and lipid peroxidation products. Similarly, tissue specific reaction to superoxide and hydrogen peroxide accumulation were distinctly demarcated in two species significantly. As a whole, the cellular responses and metabolite distribution to 2,4-D sensitization are the features to describe bio-indices for aquatic fern species Azolla with comparison to angiospermic species Vernonia.

Hardening with salicylic acid induces concentration-dependent changes in abscisic acid biosynthesis of tomato under salt stress

The role of salicylic acid (SA) in the control of abscisic acid (ABA) biosynthesis is controversial although both plant growth regulators may accumulate in tissues under abiotic and biotic stress conditions. Hardening of tomato plants to salinity stress with 10(-4)M SA ("high SA") resulted in an up-regulation of ABA biosynthesis genes, zeaxanthin epoxidase (SlZEP1), 9-cis-epoxycarotenoid dioxygenase (SlNCED1) and aldehyde oxidases (SlAO1 and SlAO2) in the roots and led to ABA accumulation both in root and leaf tissues. In plants pre-treated with lower concentration of SA (10(-7)M, "low SA"), the up-regulation of SlNCED1 in the roots promoted ABA accumulation in the root tissues but the hormone concentration remained at control level in the leaves. Salt stress induced by 100mM NaCl reduced the transcript abundance of ABA biosynthetic genes and inhibited SlAO activity in plants hardened with "high SA", but the tissues maintained root ABA level over the untreated control. The combined effect of "high SA" and ABA under salt stress led to partially recovered photosynthetic activity, reduced ethylene production in root apices, and restored root growth, which is one of the main features of salt tolerance. Unlike "high SA", hardening with "low SA" had no influence on ethylene production, and led to reduced elongation of roots in plants exposed to 100mM NaCl. The up-regulation of carotenoid cleavage dioxygenases SlCCD1A and SlCCD1B by SA, which produce apocarotenoids, may open new pathways in SA sensing and signalling processes.

Plant glutathione peroxidases: emerging role of the antioxidant enzymes in plant development and stress responses

The plant glutathione peroxidase (GPX) family consists of multiple isoenzymes with distinct subcellular locations which exhibit different tissue-specific expression patterns and environmental stress responses. Contrary to most of their counterparts in animal cells, plant GPXs contain cysteine instead of selenocysteine in their active site and while some of them have both glutathione peroxidase and thioredoxin peroxidase functions, the thioredoxin regenerating system is much more efficient in vitro than the glutathione system. At present, the function of these enzymes in plants is not completely understood. The occurrence of thiol-dependent activities of plant GPX isoenzymes suggests that - besides detoxification of H2O2 and organic hydroperoxides - they may be involved in regulation of the cellular redox homeostasis by maintaining the thiol/disulfide or NADPH/NADP(+) balance. GPXs may represent a link existing between the glutathione- and the thioredoxin-based system. The various thiol buffers, including Trx, can affect a number of redox reactions in the cells most probably via modulation of thiol status. It is still required to identify the in vivo reductant for particular GPX isoenzymes and partners that GPXs interact with specifically. Recent evidence suggests that plant GPXs does not only protect cells from stress induced oxidative damage but they can be implicated in plant growth and development. Following a more general introduction, this study summarizes present knowledge on plant GPXs, highlighting the results on gene expression analysis, regulation and signaling of Arabidopsis thaliana GPXs and also suggests some perspectives for future research.

Opposite extremes in ethylene/nitric oxide ratio induce cell death in suspension culture and root apices of tomato exposed to salt stress

The plant hormone ethylene or the gaseous signalling molecule nitric oxide (NO) may enhance salt stress tolerance by maintaining ion homeostasis, first of all K+/Na+ ratio of tissues. Ethylene and NO accumulation increased in the root apices and suspension culture cells of tomato at sublethal salt stress caused by 100 mM NaCl, however, the induction phase of programmed cell death (PCD) was different at lethal salt concentration. The production of ethylene by root apices and the accumulation of NO in the cells of suspension culture did not increase during the initiation of PCD after 250 mM NaCl treatment. Moreover, cells in suspension culture accumulated higher amount of reactive oxygen species which, along with NO deficiency contributed to cell death induction. The absence of ethylene in the apical root segments and the absence of NO accumulation in the cell suspension resulted in similar ion disequilibrium, namely K+/Na+ ratio of 1.41 ± 0.1 and 1.68 ± 0.3 in intact plant tissues and suspension culture cells, respectively that was not tolerated by tomato.

Glutathione transferase supergene family in tomato: Salt stress-regulated expression of representative genes from distinct GST classes in plants primed with salicylic acid

A family tree of the multifunctional proteins, glutathione transferases (GSTs, EC 2.5.1.18) was created in Solanum lycopersicum based on homology to known Arabidopsis GSTs. The involvement of selected SlGSTs was studied in salt stress response of tomato primed with salicylic acid (SA) or in un-primed plants by real-time qPCR. Selected tau GSTs (SlGSTU23, SlGSTU26) were up-regulated in the leaves, while GSTs from lambda, theta, dehydroascorbate reductase and zeta classes (SlGSTL3, SlGSTT2, SlDHAR5, SlGSTZ2) in the root tissues under salt stress. Priming with SA exhibited a concentration dependency; SA mitigated the salt stress injury and caused characteristic changes in the expression pattern of SlGSTs only at 10(-4) M concentration. SlGSTF4 displayed a significant up-regulation in the leaves, while the abundance of SlGSTL3, SlGSTT2 and SlGSTZ2 transcripts were enhanced in the roots of plants primed with high SA concentration. Unexpectedly, under high salinity the SlDHAR2 expression decreased in primed roots as compared to the salt-stressed plants, however, the up-regulation of SlDHAR5 isoenzyme contributed to the maintenance of DHAR activity in roots primed with high SA. The members of lambda, theta and zeta class GSTs have a specific role in salt stress acclimation of tomato, while SlGSTU26 and SlGSTF4, the enzymes with high glutathione conjugating activity, characterize a successful priming in both roots and leaves. In contrast to low concentration, high SA concentration induced those GSTs in primed roots, which were up-regulated under salt stress. Our data indicate that induction of GSTs provide a flexible tool in maintaining redox homeostasis during unfavourable conditions.

Depollution potential of three macrophytes: exudated, wall-bound and intracellular peroxidase activities plus intracellular phenol concentrations

The aim of this study was to investigate the potential role of three macrophyte species (Iris pseudacorus, Typha latifolia and Phragmites australis) for detoxication of xenobiotics, and to study their variations with seasons or concentrations of sewage sludge from the food industry. For this purpose, some aspects of the green liver concept were explored through peroxidase measurements in three compartments in roots: intracellular, cell wall and extracellular. In addition, phenol concentrations were also measured in order to assess heavy metal detoxication potential. Enzyme activities and phenol concentrations were overall lower in winter according to the phenological stages and some sludge effects occurred. Results show that P. australis roots exuded and contained more peroxidase in all seasons: 17 U/g (1373 U/g protein), 0.8 U/g (613 U/g protein) and 4.8 U/g (1329 U/g protein) in intracellular compartments, cell wall and exudates, respectively. In contrast, the highest phenol concentration was found in I. pseudacorus roots: 3.58 mg eq. [corrected] gallic acid/g. Hence, in constructed wetlands, P. australis is suitable for organic waste water treatment, while I. pseudacorus should be used in the case of waters highly charged with heavy metals.

Glutathione transferase activity and expression patterns during grain filling in flag leaves of wheat genotypes differing in drought tolerance: Response to water deficit

Total glutathione S-transferase (GST, EC 2.5.1.18) and glutathione peroxidase (GPOX) activity were measured spectrophotometrically in Triticum aestivum cv. MV Emese and cv. Plainsman (drought tolerant) and cv. GK Elet and Cappelle Desprez (drought-sensitive) flag leaves under control and drought stress conditions during the grain-filling period, in order to reveal possible roles of different GST classes in the senescence of flag leaves. Six wheat GSTs, members of 3 GST classes, were selected and their regulation by drought and senescence was investigated. High GPOX activity (EC 1.11.1.9) was observed in well-watered controls of the drought-tolerant Plainsman cultivar. At the same time, TaGSTU1B and TaGSTF6 sequences, investigated by real-time PCR, showed high-expression levels that increased with time, indicating that the gene products of these genes may play important roles in monocarpic senescence of wheat. Expression of these genes was also induced by drought stress in all of the four investigated cultivars, but extremely high transcript amounts were detected in cv. Plainsman. Our data indicate genotypic variations of wheat GSTs. Expression levels and early induction of two senescence-associated GSTs under drought during grain filling in flag leaves correlated with high yield stability.