Salicylic Acid Application Mitigates Oxidative Damage and Improves the Growth Performance of Barley under Drought Stress

Drought is a severe environmental constraint, causing a significant reduction in crop productivity across the world. Salicylic acid (SA) is an important plant growth regulator that helps plants cope with the adverse effects induced by various abiotic stresses. The current study investigated the potential effects of SA on drought tolerance efficacy in two barley (Hordeum vulgare) genotypes, namely BARI barley 5 and BARI barley 7. Ten-day-old barley seedlings were exposed to drought stress by maintaining 7.5% soil moisture content in the absence or presence of 0.5, 1.0 and 1.5 mM SA. Drought exposure led to severe damage to both genotypes, as indicated by phenotypic aberrations and reduction of dry biomass. On the other hand, the application of SA to drought-stressed plants protected both barley genotypes from the adverse effects of drought, which was reflected in the improvement of phenotypes and biomass production. SA supplementation improved relative water content and proline levels in drought-stressed barley genotypes, indicating the osmotic adjustment functions of SA under water-deficit conditions. Drought stress induced the accumulation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide (O₂ ^•− ), and the lipid peroxidation product malondialdehyde (MDA) in the leaves of barley plants. Exogenous supply of SA reduced oxidative damage by restricting the accumulation of ROS through the stimulation of the activities of key antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GPX). Among the three-applied concentrations of SA, 0.5 mM SA exhibited better mitigating effects against drought stress considering the phenotypic performance and biochemical data. Furthermore, BARI barley 5 showed better performance under drought stress than BARI barley 7 in the presence of SA application. Collectively, our results suggest that SA played a crucial role in improving water status and antioxidant defense strategy to protect barley plants from the deleterious effects of water deficiency.     

外源硫化氢和水杨酸对盐胁迫下加工番茄幼苗生长与生理特性的影响

以加工番茄KT-7为材料,在水培条件下,研究外源水杨酸(SA,0.15 mmol/L)、硫化氢(H2S)供体硫氢化钠(NaHS,50 mmol/L)对150 mmol/L NaCl胁迫下加工番茄幼苗的渗透调节、活性氧代谢和快速叶绿素荧光的影响,以探讨H2S和SA这2种信号分子协同作用、以及实际生产中缓解加工番茄幼苗盐胁...     

The alternative pathway in cucumber seedlings under low temperature stress was enhanced by salicylic acid

The alternative pathway is a cyanide-resistant and non-phosphorylatory electron transport pathway in mitochondria of higher plants. Alternative oxidase (AOX) is the terminal oxidase of this pathway. Our present study investigated the effect of exogenous salicylic acid (SA) on alternative pathway in cucumber (Cucumis sativus L.) seedlings under low temperature stress. Results showed that during the process of low temperature stress, the alternative pathway capacity was enhanced as AOX expression increased in SA pretreated seedlings. Compared with seedlings without SA pretreatment, slower decrease of relative water content and lower levels of electrolyte leakage, H₂O₂ and malonyldialdehyde content were detected in SA pretreated seedlings. These results indicated that SA could alleviate the injury caused by low temperature on cucumber seedlings. Since the special protective functions of alternative pathway and AOX in plants, we suggested that the alternative pathway was related to SA-mediated plant resistance to environmental stresses such as low temperature.     

Evidence for the involvement of nitric oxide and reactive oxygen species in osmotic stress tolerance of wheat seedlings: Inverse correlation between leaf abscisic acid accumulation and leaf water loss

Nitric oxide (NO) and reactive oxygen species (ROS) play important roles in both abscisic acid (ABA) signaling and stress-induced ABA accumulation. However, little is known about their physiological roles in the whole plant. In this study, the effects of NO and ROS on leaf water control and the roles of ABA were determined using wheat (Triticum aestivum L.) seedlings. As compared with the control, osmotic stress reduced leaf water loss (LWL) while it increased leaf ABA content. The effects of osmotic stress on LWL and ABA contents were partially reversed by NO scavengers or NO synthase (NOS) inhibitors. Furthermore, sodium nitroprusside (SNP) at concentrations between 0.01 and 10 mM all reduced LWL efficiently and induced ABA accumulation in a dose-dependent manner. When ABA synthesis was inhibited by fluridone or actidione, the effects of SNP on LWL were partially reversed. These results suggest that NO is involved in leaf water maintenance of wheat seedlings under osmotic stress, and one of the possible mechanisms is by stimulating ABA synthesis. The ROS scavengers used in our experiments had no effects on either LWL or ABA accumulation induced by osmotic stress. However, all ROS induced LWL reduction and ABA accumulation significantly. Hydrogen peroxide had the same effects as SNP on LWL and induced ABA accumulation in a dose-dependent manner but had a maximal effect at 1 mM. Fluridone reversed the effects of H₂O₂ on both LWL reduction and ABA accumulation, while actidione had no effect. These results suggest that ROS are also involved in leaf water maintenance of wheat seedlings by stimulating ABA biosynthesis, but with a different mechanism to that of NO. The ABA-independent mechanism in NO/ROS regulation of leaf water balance is discussed, in relation to our results.     

WGA reduces the level of oxidative stress in wheat seedlings under salinity

Protective effect of exogenous wheat germ agglutinin (WGA) on wheat seedling (Triticum aestivum L.) during salinity stress was studied. In particular, we examined the state of pro- and antioxidant systems as well as the level of peroxide oxidation of lipids and electrolyte leakage under control conditions and when stressed with NaCl. Generation of superoxide anions and activity of both superoxide dismutase (SOD) and peroxidase increased during saline stress. Accumulation of O₂ ^·− resulted in peroxide oxidation of lipids and electrolyte leakage in response to stress. The injurious effect of salinity on root growth of seedlings was manifested by a decreased mitotic index (MI) in apical root meristem. This study show that WGA pretreatment decreased salt-induced superoxide anion generation, SOD and peroxidase activities, levels of lipid peroxidation and electrolytes leakage as well as correlating with a reduction in the inhibition of root apical meristem mitotic activity in salt-treated plants. This suggests that exogenous WGA reduced the detrimental effects of salinity-induced oxidative stress in wheat seedlings. Thus WGA effects on a balance of reactive oxygen species (ROS) and activities of antioxidant enzymes may provide an important contribution to a range of the defense reactions induced by this lectin in wheat plants.     

The effect of reactive oxygen species on ethylene production induced by osmotic stress in etiolated mungbean seedling

After 10 h osmotic stress in 25% polyethylene glycol (PEG6000) solution (–1.8 MPa) at 25 °C in darkness, the etiolated mungbean seedlings were transferred to pure water for recovery. The ethylene release rate and the level of reactive oxygen species (ROS), including superoxide radical (O₂^–) and hydrogen peroxide (H₂O₂), were investigated during the recovery process. The results showed that ethylene production rate and amount of ROS increased dramatically after osmotic stress, and a close correlation was observed between ethylene release rate and concentrations of ROS. Inhibitors of ethylene biosynthesis, aminoethoxyvinylglycine (AVG) or aminooxyacetic acid (AOA), could reduce the ethylene release rate, but had no significant influence to the content of O₂^– and H₂O₂. As well as, silver thiosulfate (STS), an inhibitor of ethylene action, exhibited no obvious effect to the concentration of ROS, showing stress-inducible ethylene was not the cause for the increase of stress-inducible ROS. On the other hand, exogenous generator of superoxide radical (methylviologen, MV, or sodium dithionite, Na₂S₂O₄) could enhance the ethylene production evidently, which could be inhibited by exogenous scavenger of superoxide radical (superoxide dismutase, SOD, or 1, 4-diazabicyclo (2,2,2) octane, DABCO). However, either exogenous H₂O₂ or catalase (CAT) had no significant influence on ethylene production. The results suggested that it was superoxide radical but not H₂O₂which was involved directly in osmotic stress-inducible ethylene biosynthesis. The dual-role of superoxide radical on stress ethylene biosynthesis was also discussed.     

24-表油菜素内酯预处理对干旱胁迫下葡萄幼苗抗氧化系统和渗透调节物质的影响

以酿酒葡萄‘雷司令’(Riesling)一年生营养袋扦插苗为材料,采用人工气候室水培试验,考察在聚乙二醇6000(PEG)模拟干旱条件下,不同浓度(0.05、0.10和0.20mg/L)24-表油菜素内酯(EBR)预处理对‘雷司令’幼苗活性氧、抗氧化物质、渗透调节物质含量和抗氧化酶活性的影响,以揭示EBR预处理对干旱胁迫下葡萄幼苗的抗旱机理。结果显示:(1)与正常生长(对照)相比,干旱胁迫显著提高葡萄幼苗叶片中超氧阴离子自由基(■)、过氧化氢(H_2O_2)和丙二醛(MDA)含量;与干旱胁迫处理(PEG)相比,不同浓度EBR预处理均可降低叶片中■、H_2O_2和MDA的含量。(2)与对照相比,PEG处理显著降低葡萄幼苗叶片的抗坏血酸(AsA)和还原型谷胱甘肽(GSH)含量;与PEG处理相比,各浓度EBR预处理均可显著提高葡萄叶片AsA与GSH的含量,且以0.10mg/LEBR处理效果最好。(3)随着干旱胁迫时间的延长,葡萄幼苗叶片中的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)与抗坏血酸过氧化物酶(APX)活性均呈先上升后下降的变化趋势,而在正常生长条件下酶活性基本保持不变;EBR预处理的葡萄叶片SOD、CAT、POD和APX活性均始终高于同期PEG处理。(4)PEG处理条件下,渗透调节物质脯氨酸和可溶性蛋白的含量整体高于对照;与PEG处理相比,不同浓度EBR预处理在干旱胁迫中后期均能显著提高葡萄叶片中脯氨酸和可溶性蛋白含量。研究表明,在干旱胁迫下,外源EBR预处理能够提高葡萄叶片抗氧化系统酶活性和渗透调节物质含量,有效降低干旱胁迫诱导的活性氧过度积累及膜脂过氧化程度,提高葡萄幼苗的抗旱能力,且以0.10mg/L EBR处理效果最佳。     

Potential of salicylic acid activity derived from stress-induced (water) Tomato against Meloidogyne incognita

Plants have evolved several types of sophisticated defence mechanisms to protect themselves from enemies in which the signalling molecules such as salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) often play crucial roles. An experiment was conducted to investigate the water induced stress in young tomato plants (Lycopersicon esculentum var. Pusa Ruby) during water deprivation and after relief from stress in association with salicylic acid. Application of SA or certain analogues such as aspirin induces expression of pathogenesis-related proteins (PR) in plants which serve as molecular markers for the systemic acquired response (SAR). In plants, the production of reactive oxygen species (ROS), such as superoxide radical (O₂), hydroxyl radical (OH) and hydrogen peroxide (H₂O₂), is also common in metabolic and physiological processes. Similar to the defence-regulating compounds such as SA and JA, plant-derived ET is also known to be involved in disease resistance. The role of ROS or ET could be investigated which was carried out in the present study to know the osmotic stress mediated resistance by SA against Meloidogyne incognita in tomato plants.     

Salicylic acid and nitric oxide alleviate osmotic stress in wheat (Triticum aestivum L.) seedlings

Salicylic acid (SA) and nitric oxide (NO) are reported to alleviate the damaging effects of stress in plants rather similarly when applied at appropriate low concentrations. An experiment was therefore conducted to study the impact of SA, sodium nitroprusside (SNP; as NO donor), and methylene blue (MB; as a guanylate cyclase inhibitor) on wheat seedling performance under osmotic stress. Osmotic stress significantly reduced shoot fresh weight (SFW), chlorophyll contents (Chla, Chlb, total Chl), and membrane stability index (MSI) and also increased malondialdehyde (MDA) level, lipoxygenase (LOX) activity, and hydrogen peroxide production. Moreover, enzymatic antioxidant activities including superoxide dismutase, guaiacol peroxidase, and glutathione reductase activity were enhanced under osmotic stress. On the contrary, SA or SNP pretreatment reduced the damaging effects of osmotic stress by further enhancing the antioxidant activities that led to increased SFW, Chl, and MSI and reduced MDA level and LOX activity. However, pretreatment of plants with MB reversed or reduced the protective effects of SA and SNP suggesting that the protective effects were likely attributed to NO signaling. Therefore, NO may act as downstream of SA signaling in reduction of induced oxidative damage in wheat seedlings.     

Effect of osmotic stress and sodium nitroprusside pretreatment on proline metabolism of wheat seedlings

Effect of osmotic stress and sodium nitroprusside (SNP, NO donor) pretreatment on growth and proline metabolism of wheat seedlings was investigated. Polyethylene glycol 6000 treatment for 2, 4 and 6 d could be termed as mild, moderate and severe stress, respectively, according to decrease in the relative water content. Severe osmotic stress significantly decreased the growth and photochemical efficiency, and increased proline content due to activation of its synthesis. 0.2 mM SNP pretreatment enhanced growth of wheat seedlings, increased variable to maximum fluorescence ratio (F_v/F_m) and fluorescence yield, while decreased proline content. However, 2 mM SNP retarded the seedlings growth and chlorophyll a fluorescence, and increased proline accumulation. Our results showed that NO might be involved in the regulation of osmotic stress in a concentration-dependent manner.     

The dual effects of salicylic acid on dehydrin accumulation in water-stressed barley seedlings

Dehydrins are a group of plant proteins that usually accumulate in response to environmental stresses. They are proposed to play specific protective roles in plant cells. Present study showed that the accumulation of dehydrins in water-stressed barley (Hordeum vulgare L.) seedlings was influenced by their treatment with salicylic acid (SA). The level of dehydrin proteins was increased by 0.20 mM SA, but decreased by 0.50 mM SA treatment. Both mRNA expression and protein accumulation of a typical barley dehydrin, DHN5, were enhanced by SA treatment when SA concentrations were lower than 0.25 mM. However, the higher SA concentrations significantly decreased the protein level of DHN5 despite of a stable mRNA level. Our results also showed that low SA concentrations (less than 0.25 mM) decreased the electrolyte leakage and malondialdehyde (MDA) and H₂O₂ contents in water-stressed barley seedlings. But high SA concentrations (more than 0.25 mM) enhanced H₂O₂ accumulation, tended to cause more electrolyte leakage, and increase MDA content. These data indicated that SA could up-regulate the dehydrin gene expression and protein accumulation. Since the protective role of dehydrins in plant cells, such effect could be an important reason for the SA-mediated alleviation on water stress injury. But excessive SA could suppress the accumulation of dehydrin proteins and aggravate the oxidative damage. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 3, pp. 388–394. This text was submitted by the authors in English.     

Cross-talk between salicylic acid and NaCl-generated reactive oxygen species and nitric oxide in tomato during acclimation to high salinity

Hydrogen peroxide (H₂O₂) and nitric oxide (NO) generated by salicylic acid (SA) are considered to be functional links of cross‐tolerance to various stressors. SA‐stimulated pre‐adaptation state was beneficial in the acclimation to subsequent salt stress in tomato (Solanum lycopersicum cv. Rio Fuego). At the whole‐plant level, SA‐induced massive H₂O₂ accumulation only at high concentrations (10^?3–10^?2M), which later caused the death of plants. The excess accumulation of H₂O₂ as compared with plants exposed to 100 mM NaCl was not associated with salt stress response after SA pre‐treatments. In the root tips, 10^?3–10^?2M SA triggered the production of reactive oxygen species (ROS) and NO with a concomitant decline in the cell viability. Sublethal concentrations of SA, however, decreased the effect of salt stress on ROS and NO production in the root apex. The attenuation of oxidative stress because of high salinity occurred not only in pre‐adapted plants but also at cell level. When protoplasts prepared from control leaves were exposed to SA in the presence of 100 mM NaCl, the production of NO and ROS was much lower and the viability of the cells was higher than in salt‐treated samples. This suggests that, the cross‐talk of signalling pathways induced by SA and high salinity may occur at the level of ROS and NO production. Abscisic acid (ABA), polyamines and 1‐aminocyclopropane‐1‐carboxylic acid, the compounds accumulating in pre‐treated plants, enhanced the diphenylene iodonium‐sensitive ROS and NO levels, but, in contrast to others, ABA and putrescine preserved the viability of protoplasts.     

高温胁迫下外源褪黑素对黄瓜幼苗活性氧代谢的影响

以黄瓜品种‘津春4号’为试材,用叶面喷施的方法,研究了高温胁迫条件下外源褪黑素(melatonin,MT)对黄瓜幼苗活性氧（ROS）代谢的影响.结果表明：外源MT能显著降低高温胁迫下黄瓜叶片超氧阴离子自由基（O₂^-.）产生速率、过氧化氢（H₂O₂）含量、电解质漏渗率（relative electric conductivity, REC）及丙二醛(MDA)含量,增强黄瓜幼苗叶片中超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性,提高抗坏血酸（AsA）、谷胱甘肽（GSH）及可溶性蛋白质含量.说明MT预处理能抑制高温胁迫条件下黄瓜幼苗体内ROS的产生,提高抗氧化酶系的活性及抗氧化物质的含量,降低膜质过氧化水平,保护脂膜的完整性,减少电解质的外渗,减轻高温胁迫对幼苗造成的伤害,提高幼苗抗高温胁迫的能力.     

硝基苯酚胁迫下外源褪黑素对水稻幼苗生长及生理特性的影响

采用液体培养实验方法,研究硝基苯酚胁迫对水稻(Oryza sativa L.)幼苗生长、抗氧化特性、光系统Ⅱ(PSⅡ)光合特性的影响,以及添加外源褪黑素对缓解硝基苯酚胁迫的作用。结果显示,随着硝基苯酚胁迫浓度的升高,水稻幼苗株高、根长、地下部干重、地上部干重、全株干重和叶片PSⅡ实际光化学效率[Y(Ⅱ)]、光化学淬灭系数(q P)、PSⅡ电子传递速率(ETR)、叶绿素含量均有所下降,而叶片非光化学淬灭系数(qN、NPQ)上升;同时,根系活性氧[过氧化氢(H_2O_2)和超氧阴离子(O·-2)]积累量、抗氧化酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)]活性,以及渗透调节物质(可溶性蛋白和可溶性糖)含量呈先升高后降低的趋势。在非硝基苯酚胁迫下,与对照组相比,添加外源褪黑素显著提高了幼苗地下部干重、根系可溶性糖含量和SOD活性、叶片PSⅡ光化学效率和叶绿素含量。与单独添加硝基苯酚处理相比,硝基苯酚+褪黑素复合处理显著缓解了硝基苯酚胁迫对幼苗生长、叶片PSⅡ光化学效率和叶绿素合成的抑制作用;降低了根系活性氧水平、抗氧化酶活性和渗透调节物质含量。研究结果表明添加外源褪黑素能够显著缓解硝基苯酚胁迫对水稻幼苗生长、根系活性氧水平、抗氧化酶活性、叶片PSⅡ光化学效率及叶绿素合成的不良影响,提高水稻幼苗对硝基苯酚胁迫的适应性。     

外源SA和NO对NaCl胁迫下番茄幼苗生长、光合及离子分布的影响

以番茄(Lycopersicon esculentum Mill.)品种‘秦丰保冠’为试材,采用营养液培养法,研究单独和复配施用外源水杨酸(SA)、一氧化氮(NO)供体硝普钠(SNP)对100mmol/L NaCl胁迫下番茄幼苗生长、光合及离子分布的影响。结果表明:(1)单独和复配外施SA、SNP均能有效抑制NaCl胁迫下番茄幼苗叶片光合色素(Chla、Chlb、Chla+b和Car)含量、Chla/b值、净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、瞬时水分利用效率(WUEt)、表观光能利用效率(LUEapp)和表观CO2利用效率(CUEapp)的下降及Car/Chla+b值和胞间CO2浓度(Ci)的升高,并以SA和SNP复配处理效果最明显。(2)NaCl胁迫下,外源SA、SNP单独和复配处理的番茄幼苗各器官(叶、茎和根)中Cl-、Na+含量和Na+/K+、Na+/Ca2+、Na+/Mg2+值显著降低,而K+、Ca2+和Mg2+的含量却不同程度提高,其中以SA和SNP复配处理效果最好。(3)单独和复配外施SA、SNP均能有效减轻NaCl胁迫对番茄幼苗生长的抑制作用,并促进各器官生物量的积累和壮苗的形成,且以SA和SNP复配处理效果更佳。研究表明,复配外施SA和SNP在诱导番茄幼苗提高抗(耐)盐能力方面具有协同增效作用。     

Protein carbonylation in barley seedling roots caused by aluminum and proton toxicity is suppressed by salicylic acid

Proton (H⁺) and aluminum (Al³⁺) toxicities are major factors limiting crop production on acid soils. To study whether salicylic acid (SA) is functional in alleviating protein damage caused by H⁺ and Al³⁺ toxicities, an investigation of the antioxidant defense response regulated by SA was carried out on barley (Hordeum vulgare L.) seedlings under H⁺, Al³⁺, and combined stresses. It was found that the relative root elongation of seedlings, which grew in the solutions supplemented with SA, was significantly higher than that of seedlings without SA treatment after 24-h treatments with H⁺, Al³⁺, and combined stresses. The lesser amount of carbonylated proteins with molecular weights ranging from 14.4 to 97 kD, was accumulated in seedlings treated with SA than that in the seedlings without SA treatment. The higher activities of antioxidant enzymes and lesser content of MDA were observed in seedlings treated with SA compared with the seedlings without SA treatment. Moreover, the nitroblue tetrazolium staining of roots showed that ROS accumulation was decreased by SA treatments. This study suggested that SA could alleviate cell damage caused by H⁺ and Al³⁺ toxicities on acid soils by both activating antioxidant defense responses and reducing the contents of carbonylated proteins caused by ROS in barley seedlings.     

Endogenous salicylic acid accumulation is required for chilling tolerance in cucumber (Cucumis sativus L.) seedlings

Salicylic acid (SA) is an important plant hormone, and its exogenous application can induce tolerance to multiple environmental stresses in plants. In this study, we examine the potential involvement of endogenous SA in response to chilling in cucumber (Cucumis sativus L.) seedlings. A low temperature of 8 °C induces a moderate increase in endogenous SA levels. Chilling stimulates the enzymatic activities and the expression of genes for phenylalanine ammonia-lyase (PAL) and benzoic acid-2-hydroxylase rather than isochorismate synthase. This indicates that the PAL enzymatic pathway contributes to chilling-induced SA production. Cucumber seedlings pretreated with SA biosynthesis inhibitors accumulate less endogenous SA and suffer more from chilling damage. The expression of cold-responsive genes is also repressed by SA inhibitors. The reduction in stress tolerance and in gene expression can be restored by the exogenous application of SA, confirming the critical roles of SA in chilling responses in cucumber seedlings. Furthermore, the inhibition of SA biosynthesis under chilling stress results in a prolonged and enhanced hydrogen peroxide (H₂O₂) accumulation. The application of exogenous SA and the chemical scavenger of H₂O₂ reduces the excess H₂O₂ and alleviates chilling injury. In contrast, the protective effects of SA are negated by foliar spraying with high concentrations of H₂O₂ and an inhibitor of the antioxidant enzyme. These results suggest that endogenous SA is required in response to chilling stress in cucumber seedlings, by modulating the expression of cold-responsive genes and the precise induction of cellular H₂O₂ levels.     

Physiological and Biochemical Mechanisms of Exogenous Calcium Chloride on Alleviating Salt Stress in Two Tartary Buckwheat (<i>Fagopyrum tataricum</i>) Varieties Differing in Salinity Tolerance

Salt stress is one of the most serious abiotic stresses limiting plant growth and development. Calcium as an essential nutrient element and important signaling molecule plays an important role in ameliorating the adverse effect of salinity on plants. This study aimed to investigate the impact of exogenous calcium on improving salt tolerance in Tartary buckwheat cultivars, cv. Xinong9920 (salt-tolerant) and cv. Xinong9909 (salt-sensitive). Four-week-old Tartary buckwheat seedlings under 100 mM NaCl stress were treated with and without exogenous calcium chloride (CaCl₂), Ca²⁺ chelator ethylene glycol tetraacetic acid (EGTA) and Ca²⁺-channel blocker lanthanum chloride (LaCl₃) for 10 days. Then, some important physiological and biochemical indexes were determined. The results showed that salt stress significantly reduced seedling growth, decreased photosynthetic pigments, inhibited antioxidants and antioxidant enzyme activities. However, it increased the reactive oxygen species (ROS) levels in the two Tartary buckwheat cultivars. Exogenous 10 mM CaCl₂ application on salt-stressed Tartary buckwheat seedlings obviously mitigated the negative effects of NaCl stress and partially restored seedlings growth. Ca²⁺-treated salt-stressed seedlings diplayed a suppressed accumulation of ROS, increased the contents of total chlorophyll, soluble protein, proline and antioxidants, and elevated the activities of antioxidant enzymes compared with salt stress alone. On the contrary, the addition of 0.5 mM LaCl₃ and 5 mM EGTA on salt-stressed Tartary buckwheat seedlings exhibited the opposite effects to those with CaCl₂ treatment. These results indicate that exogenous Ca²⁺ can enhance salt stress tolerance and Ca²⁺ supplementation may be an effective practice to cultivate Tartary buckwheat in saline soils.     

Implication of ABA and proline on cell membrane injury of water deficit stressed barley seedlings

The aim of this work was to examine the ability of ABA and proline to counteract the deleterious effect of water deficit stress on cell membrane injuries. Six-day-old seedlings of two barley genotypes (cv. Aramir, line R567) were treated with ABA (2·10⁻⁴ M) or proline (0.1 M) for 24 h, and then subjected to osmotic stress for 24h, by immersing their roots in polyethylene glycol (PEG 6000) solution of osmotic potential of −1.0 MPa and −1.5 MPa or by submerging the leaf pieces in PEG solution of osmotic potential of −1.6 MPa. Pretreatment of plants with ABA and proline caused an increase of free proline level in the leaves. Plants treated with ABA exhibited a lower membrane injury index under water stress conditions than those untreated even when no effect of this hormone on RWC in the leaves of stressed plants was observed. Pretreatment of plants with proline prevented to some extent membrane damage in leaves of the stressed seedlings, but only in the case when stress was imposed to roots. Improvement in water status of leaves was also observed in seedlings pretreatment with proline. The protective effect of both ABA and proline was more pronounced in line R567 that exhibited higher membrane injury under water deficit stress conditions.