The role of salicylic acid in response of two rice cultivars to chilling stress

Two rice (Oryza sativa L.) cultivars differing in chilling sensitivity, Changbaijiu (chilling-tolerant) and Zhongjian (chilling-sensitive) were pre-treated with 0.5, 1.0 and 2.0 mM salicylic acid (SA) for 24 h before chilling at 5°C for 1 d. Chilling induced SA accumulation, particularly conjugated SA in both leaves and roots of the two rice cultivars. After SA administration, SA accumulated in the roots of both cultivars at a concentration-dependent manner, whereas only a slight increase was observed in their leaves. Conjugated SA accounted for most of the increase. The beneficial effect of SA treatment on protecting rice seedlings from chilling injury was not observed at any concentration in either cultivar. Pre-treatment with SA even decreased their chilling tolerance confirmed by increased electrolyte leakage and lipid peroxidation. Further, most of the activities of antioxidant enzymes decreased or remained unchanged in leaves and roots of SA pre-treated seedlings after chilling. These results implied that down-regulation of antioxidant defence might be involved in the reduction of chilling tolerance in SA-pre-treated plants.     

The role of calcium,silicon and salicylic acid treatment in protection of canola plants against boron toxicity stress

Boron (B) toxicity often limits crop yield and the quality of production in agricultural areas. Here, we investigated the effects of calcium (Ca), silicon (Si) and salicylic acid (SA) on development of B toxicity, B allocation in canola (Brassica napus cultivar Sarw 4) and its role in non-enzymatic antioxidants in relation to yield of this cultivar under B toxicity. Canola seedlings were subjected to four B levels induced by boric acid in the absence or presence of Ca, Si and SA. The results showed that Ca, Si and SA addition ameliorated the inhibition in canola growth, water content (WC), and improved siliqua number, siliqua weight and seed index. The B content in shoots and roots and total B accumulation in the whole plant were increased in control plants under B-toxicity-stress, and these parameters were significantly decreased by addition of Ca, Si and SA. The shoot ascorbate pool (ascorbate, AsA, and dehydroascorbate, DHA), α-tocopherol and phenolics (free and bound) were increased under B toxicity, and were significantly decreased in most cases by addition of Ca, Si and SA, except α-tocopherol, which increased at low B levels (0, 25 and 50 mg kg soil^?1). The glutathione content did not obviously change by B stress, while added Ca, Si and SA inhibited its accumulation under B stress. In addition, B toxicity reduced the shoot flavonoids content; however, this reduction was not alleviated by the use of Ca, Si and SA treatments. It could be concluded that growth and yield of canola plants grown under high B concentration improved after external application of Ca, Si or SA.     

Constitutively elevated salicylic acid signals glutathione-mediated nickel tolerance in Thlaspi nickel hyperaccumulators

Progress is being made in understanding the biochemical and molecular basis of nickel (Ni)/zinc (Zn) hyperaccumulation in Thlaspi; however, the molecular signaling pathways that control these mechanisms are not understood. We observed that elevated concentrations of salicylic acid (SA), a molecule known to be involved in signaling induced pathogen defense responses in plants, is a strong predictor of Ni hyperaccumulation in the six diverse Thlaspi species investigated, including the hyperaccumulators Thlaspi goesingense, Thlaspi rosulare, Thlaspi oxyceras, and Thlaspi caerulescens and the nonaccumulators Thlaspi arvense and Thlaspi perfoliatum. Furthermore, the SA metabolites phenylalanine, cinnamic acid, salicyloyl-glucose, and catechol are also elevated in the hyperaccumulator T. goesingense when compared to the nonaccumulators Arabidopsis (Arabidopsis thaliana) and T. arvense. Elevation of free SA levels in Arabidopsis, both genetically and by exogenous feeding, enhances the specific activity of serine acetyltransferase, leading to elevated glutathione and increased Ni resistance. Such SA-mediated Ni resistance in Arabidopsis phenocopies the glutathione-based Ni tolerance previously observed in Thlaspi, suggesting a biochemical linkage between SA and Ni tolerance in this genus. Intriguingly, the hyperaccumulator T. goesingense also shows enhanced sensitivity to the pathogen powdery mildew (Erysiphe cruciferarum) and fails to induce SA biosynthesis after infection. Nickel hyperaccumulation reverses this pathogen hypersensitivity, suggesting that the interaction between pathogen resistance and Ni tolerance and hyperaccumulation may have played a critical role in the evolution of metal hyperaccumulation in the Thlaspi genus.     

Herbivore-induced rice resistance against rice blast mediated by salicylic acid

In agro-ecosystems,plants are important mediators of interactions between their associated herbivorous insects and microbes,and any change in plants induced by one species may lead to cascading effects on interactions with other species.Often,such effects are regulated by phytohormones such as jasmonic acid(JA)and salicylic acid(SA).Here,we investigated the tripartite interactions among rice plants,three insect herbivores(Chilo suppressalis,Cnaphalocrocis medinalis or Nilapai-vata lugens),and the causal agent of rice blast disease,the fungus Magnaporthe oryzae.We found that pre-infestation of rice by C.suppressalis or N.lugens but not by C.medinalis conferred resistance to M.oryzae.For C.suppressalis and N.lugens,insect infestation without fungal inoculation induced the accumulation of both JA and SA in rice leaves.In contrast,infestation by C.medinalis increased JA levels but reduced SA levels.The exogenous application of SA but not of JA conferred resistance against M.oryzae.These results suggest that preinfestation by C suppressalis or N.lugens conferred resistance against M.oryzae by increasing SA accumulation.These findings enhance our understanding of the interactions among rice plant,insects and pathogens,and provide valuable information for developing an ecologically sound strategy for controlling rice blast.     

The Arabidopsis aba4-1 mutant reveals a specific function for neoxanthin in protection against photooxidative stress

The aba4-1 mutant completely lacks neoxanthin but retains all other xanthophyll species. The missing neoxanthin in light-harvesting complex (Lhc) proteins is compensated for by higher levels of violaxanthin, albeit with lower capacity for photoprotection compared with proteins with wild-type levels of neoxanthin. Detached leaves of aba4-1 were more sensitive to oxidative stress than the wild type when exposed to high light and incubated in a solution of photosensitizer agents. Both treatments caused more rapid pigment bleaching and lipid oxidation in aba4-1 than wild-type plants, suggesting that neoxanthin acts as an antioxidant within the photosystem II (PSII) supercomplex in thylakoids. While neoxanthin-depleted Lhc proteins and leaves had similar sensitivity as the wild type to hydrogen peroxide and singlet oxygen, they were more sensitive to superoxide anions. aba4-1 intact plants were not more sensitive than the wild type to high-light stress, indicating the existence of compensatory mechanisms of photoprotection involving the accumulation of zeaxanthin. However, the aba4-1 npq1 double mutant, lacking zeaxanthin and neoxanthin, underwent stronger PSII photoinhibition and more extensive oxidation of pigments than the npq1 mutant, which still contains neoxanthin. We conclude that neoxanthin preserves PSII from photoinactivation and protects membrane lipids from photooxidation by reactive oxygen species. Neoxanthin appears particularly active against superoxide anions produced by the Mehler's reaction, whose rate is known to be enhanced in abiotic stress conditions.     

The role of glycinebetaine in the protection of spinach thylakoids against freezing stress

The quaternary ammonium compound glycinebetaine has been tested for cryoprotective properties, using isolated spinach thylakoids as a model membrane system. The effect of a 3-h,-20°C freezing regime on different photosynthetic parameters was measured. These parameters were the light-stimulated pH formation and dark pH decay, light-stimulated proton uptake, electron flow through photosystem II, photosystem I and total linear electron flow, and pyocyanine-mediated cyclic photophosphorylation. It was shown that below 100 mM glycinebetaine was superior as a cryoprotectant to sucrose on a molar, a molal and an activity basis. At higher concentrations, glycinebetaine was less efficient in preventing inactivation of thylakoids during freezing than sucrose. These observations are discussed in relation to the permeability of biomembranes to glycinebetaine and the colligative theory of cryoprotection. It is concluded that colligative protection is modified by direct interaction between cryoprotectant and membranes.Abbreviations Asc ascorbate - cyt f cytochrome f - DAD 2,3,5,6-tetramethyl--phenylenediamine - DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea - DCPIP 2,6-dichlorophenolidophenol - DBMIB 2,5-dibromo-3-methyl-6-isopropyl--benzoquinone - DNP-INT 1,3-dinitrophenylether of iodonitrothymol - FeCy ferricyanide - MV methylviologen (1,1-dimethyl-4-4-bipyridinium-dichloride) - PQ plastoquinone - PS I photosystem I - PS II photosystem II     

Treatment with acetyl salicylic acid protects muskmelon seedlings against drought stress

Salicylic acid (SA) is a common plant-produced signal molecule that is responsible for inducing tolerance to a number of biotic and abiotic stresses. An experiment was, therefore, conducted to test whether acetyl salicylic acid (ASA) application at various concentrations through seed soaking or foliar spray would protect muskmelon [Cucumis melo L. (reticulatus group)] seedlings, subjected to drought stress. Twenty-three-day-old plants pre-treated with ASA (0, 0.1, 0.25, 0.50 or 1.0 mM) were subjected to drought stress for 1 week in a greenhouse. ASA applied either through seed soaking or through foliar spray was effective within the range of 0.1–1 mM in providing drought stress protection in muskmelon seedlings; however, there was no difference between application methods indicating that both methods provided similar levels of protection. ASA significantly affected all seedling growth and stress indicator variables measured except leaf number and root dry weight. The best protection appeared to be obtained from seedlings pre-treated with lower concentrations of ASA. Even though both methods provided similar means of protection, due to its simplicity and practicality, soaking muskmelon seeds prior to sowing in up to 0.5 mM ASA would be a more desirable method.     

The role of salicylic acid and jasmonic acid in pathogen defence

Phytohormones are not only instrumental in regulating developmental processes in plants but also play important roles for the plant's responses to biotic and abiotic stresses. In particular, abscisic acid, ethylene, jasmonic acid, and salicylic acid have been shown to possess crucial functions in mediating or orchestrating stress responses in plants. Here, we review the role of salicylic acid and jasmonic acid in pathogen defence responses with special emphasis on their function in the solanaceous plant potato.     

Vitamin E protects against photoinhibition and photooxidative stress in Arabidopsis thaliana

Vitamin E is considered a major antioxidant in biomembranes, but little evidence exists for this function in plants under photooxidative stress. Leaf discs of two vitamin E mutants, a tocopherol cyclase mutant (vte1) and a homogentisate phytyl transferase mutant (vte2), were exposed to high light stress at low temperature, which resulted in bleaching and lipid photodestruction. However, this was not observed in whole plants exposed to long-term high light stress, unless the stress conditions were extreme (very low temperature and very high light), suggesting compensatory mechanisms for vitamin E deficiency under physiological conditions. We identified two such mechanisms: nonphotochemical energy dissipation (NPQ) in photosystem II (PSII) and synthesis of zeaxanthin. Inhibition of NPQ in the double mutant vte1 npq4 led to a marked photoinhibition of PSII, suggesting protection of PSII by tocopherols. vte1 plants accumulated more zeaxanthin in high light than the wild type, and inhibiting zeaxanthin synthesis in the vte1 npq1 double mutant resulted in PSII photoinhibition accompanied by extensive oxidation of lipids and pigments. The single mutants npq1, npq4, vte2, and vte1 showed little sensitivity to the stress treatments. We conclude that, in cooperation with the xanthophyll cycle, vitamin E fulfills at least two different functions in chloroplasts at the two major sites of singlet oxygen production: preserving PSII from photoinactivation and protecting membrane lipids from photooxidation.     

Synthesis and role of glutathione in protection against oxidative stress in yeast

Summary

Glutathione (GSH) is an abundant and ubiquitous low-molecular-mass thiol with proposed roles in many cellular processes including amino acid transport, synthesis of proteins and nucleic acids, modulation of enzyme activity and metabolism of xenobiotics, carcinogens and reactive oxygen species. This review describes recent findings in the lower eukaryote Saccharomyces cerevisiae that are leading to a better understanding of the role of this peptide in eukaryotic cell metabolism. In particular, two gene products involved in maintaining the levels of reduced GSH have been studied; namely, GSH1 encoding γ-glutamylcysteine synthetase, the first step in the biosynthesis of GSH, and glutathione reductase, which recycles glutathione to its reduced form. These studies indicate that GSH is an essential metabolite in yeast, and that it is required for protection against oxidative stress produced by mitochondrial metabolism and exogenous reactive oxygen species. These findings are discussed in the light of analogous observations made in higher eukaryotes.     

Role of salicylic acid in plant abiotic stress

Salicylic acid (SA) plays many roles in plant physiology. Besides pathogenesis-related resistance, SA is involved in the response to abiotic stress. However, the effects of SA on plant resistance to abiotic stress were found contradictionary, and the actual role of SA in abiotic stress remains unresolved. Generally, deficiency of SA or a very high level of SA increase the plant susceptibility to abiotic stress. The optimal levels for the highest stress tolerance range from 0.1 mM to 0.5 mM for most plants. But the role of SA at a certain level in moderate and severe abiotic stress may be different. This can be attributed to redox regulations in plant cells. In this paper, we discuss the relationship between reactive oxygen species (ROS) and SA, and propose a subsequent intracellular signal transduction network of SA and ROS under abiotic stress. Anti-stress substances besides antioxidant enzymes induced by SA are also summarized.     

The Arabidopsis thaliana sulfiredoxin is a plastidic cysteine-sulfinic acid reductase involved in the photooxidative stress response

The 2-cysteine peroxiredoxins (2-Cys-Prxs) are antioxidants that reduce peroxides through a thiol-based mechanism. During catalysis, these ubiquitous enzymes are occasionally inactivated by the substrate-dependent oxidation of the catalytic cysteine to the sulfinic acid (-SO2H) form, and are reactivated by reduction by sulfiredoxin (Srx), an enzyme recently identified in yeast and in mammal cells. In plants, 2-Cys-Prxs constitute the most abundant Prxs and are located in chloroplasts. Here we have characterized the unique Srx gene in Arabidopsis thaliana (AtSrx) from a functional point of view, and analyzed the phenotype of two AtSrx knockout (AtSrx-) mutant lines. AtSrx is a chloroplastic enzyme displaying sulfinic acid reductase activity, as shown by the ability of the recombinant AtSrx to reduce the overoxidized 2-Cys-Prx form in vitro, and by the accumulation of the overoxidized Prx in mutant lines lacking Srx in vivo. Furthermore, AtSrx mutants exhibit an increased tolerance to photooxidative stress generated by high light combined with low temperature. These data establish that, as in yeast and in mammals, plant 2-Cys-Prxs are subject to substrate-mediated inactivation reversed by Srx, and suggest that the 2-Cys-Prx redox status and sulfiredoxin are parts of a signaling mechanism participating in plant responses to oxidative stress.     

Enzymatic defences against photooxidative stress induced by ultraviolet radiation in Arctic marine macroalgae

The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT), as well as the content of the antioxidant compound ascorbic acid, were determined in five green, seven red and ten brown macroalgal species from the Kongsfjord (Spitsbergen, Svalbard, Norway). In general, higher antioxidant enzyme activities and a higher content of ascorbic acid were measured in green algae in comparison to red and brown algae. Species from the eulittoral and upper sublittoral (Acrosiphonia penicilliformis, Monostroma arcticum, Chaetomorpha linum, Chaetomorpha melagonium, Devaleraea ramentacea, Palmaria palmata) showed higher antioxidant enzyme activities compared to species from the lower sublittoral, indicating a more efficient biochemical protection in algae exposed to higher stress conditions in the field. The activity of GR was stimulated by artificial ultraviolet radiation in the green alga M. arcticum, and in the red algae Coccotylus truncatus and Phycodrys rubens after 84 h under continuous exposure. GR activity was even higher when the UV exposure was followed by incubation in darkness for 24 h, indicating a higher elimination rate of toxic oxygen radicals under these conditions. D. ramentacea, P. palmata and A. penicilliformis did not show any significant effect of UV radiation on CAT, APX and SOD activities after 8 days of culture under laboratory conditions. However, a significant reduction in activities of GR and SOD was observed in A. penicilliformis when solar UV radiation was cut off by selective filter foils in the field, indicating a lower oxidative stress in the absence of UV radiation. Overall, the ecological success of macroalgae in the eulittoral and upper sublittoral is supported by an enhanced oxygen-reactive scavenging system, allowing fast acclimation to the changes in environmental radiation conditions.     

Jasmonic acid and salicylic acid activate a common defense system in rice

Jasmonic acid (JA) and salicylic acid (SA) play important roles in plant defense systems. JA and SA signaling pathways interact antagonistically in dicotyledonous plants, but, the status of crosstalk between JA and SA signaling is unknown in monocots. Our rice microarray analysis showed that more than half of the genes upregulated by the SA analog BTH are also upregulated by JA, suggesting that a major portion of the SA-upregulated genes are regulated by JA-dependent signaling in rice. A common defense system that is activated by both JA and SA is thus proposed which plays an important role in pathogen defense responses in rice.     

Alleviation of salt stress in lemongrass by salicylic acid

Soil salinity is one of the key factors adversely affecting the growth, yield, and quality of crops. A pot study was conducted to find out whether exogenous application of salicylic acid could ameliorate the adverse effect of salinity in lemongrass (Cymbopogon flexuosus Steud. Wats.). Two Cymbopogon varieties, Krishna and Neema, were used in the study. Three salinity levels, viz, 50, 100, and 150 mM of NaCl, were applied to 30-day-old plants. Salicylic acid (SA) was applied as foliar spray at 10^?5 M concentration. Totally, six SA-sprays were carried out at 10-day intervals, following the first spray at 30 days after sowing. The growth parameters were progressively reduced with the increase in salinity level; however, growth inhibition was significantly reduced by the foliar application of SA. With the increase in salt stress, a gradual decrease in the activities of carbonic anhydrase and nitrate reductase was observed in both the varieties. SA-treatment not only ameliorated the adverse effects of NaCl but also showed a significant improvement in the activities of these enzymes compared with the untreated stressed-plants. The plants supplemented with NaCl exhibited a significant increase in electrolyte leakage, proline content, and phosphoenol pyruvate carboxylase activity. Content and yield of essential oil was also significantly decreased in plants that received salinity levels; however, SA overcame the unfavorable effects of salinity stress to a considerable extent. Lemongrass variety Krishna was found to be more adapted to salt stress than Neema, as indicated by the overall performance of the two varieties under salt conditions.     

Central role of salicylic acid in resistance of safflower (Carthamus tinctorius L.) against salinity

The effects of salicylic acid (SA) on growth parameters and enzyme activities were investigated in salt-stressed safflower (Carthamus tinctorius L.). Twenty-five days after sowing, seedlings were treated with NaCl (0, 100, and 200?mM) and SA (1?mM), and were harvested at 21 days after treatments. Results showed that some growth parameters decreased under salinity, while malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content, phenolic compounds, and some enzyme activities increased. SA application increased some growth parameters, MDA and H₂O₂ content, and enzyme activities except catalase (CAT), which was different from the other enzymes and SA significantly reduced CAT activity in plants. These results suggest that SA-induced tolerance to salinity may be related to regulation of antioxidative responses and H₂O₂ level. Our study suggested that the resistant safflower can direct reactive oxygen species from a threat to an opportunity by using SA. Therefore, exogenous application of SA played this role through regulation of the antioxidant system.     

Protective role of S-adenosyl-L-methionine against hydrochloric acid stress in Saccharomyces cerevisiae

S-adenosyl-L-methionine (AdoMet, 1mM) protects the stationary phase cells of Saccharomyces cerevisiae against the killing effect of acid (10mM HCl, pH approximately 2). Both the acid and the acid plus AdoMet treatment for 2h increased the plasma membrane H(+)-ATPase activity; thereafter it decreased to the basal level. AdoMet partially recovered the intracellular pH (pH(in)) that dropped in presence of acid. AdoMet treatment facilitated acid induced phospholipid biosynthesis as well as membrane proliferation, which was reflected in the cellular lipid composition.