H_2S对干旱胁迫下白三叶幼苗抗氧化防御能力的影响

以‘拉丁诺’白三叶(Trifolium repens cv.‘Ladino’)为试验材料,研究外源H2S处理对PEG6 000(聚乙二醇)模拟干旱胁迫下白三叶叶片相对含水量(RWC)、膜脂过氧化、活性氧成分、抗氧化酶、抗坏血酸-谷胱甘肽循环代谢和非酶抗氧化物质的影响,以揭示H_2S调控白三叶抗旱性的生理机制。结果显示:(1)0.2 mmol/L的外源NaHS(H_2S供体)能显著提高干旱胁迫下白三叶的叶片相对含水量,维持显著较低的电解质渗透率(EL)和丙二醛(MDA)含量。(2)与直接干旱胁迫相比,干旱胁迫下外源添加NaHS处理的白三叶叶片内超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性显著增强,抗坏血酸-谷胱甘肽循环代谢中关键酶抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、单脱水抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性及其抗氧化中间产物抗坏血酸(AsA)、谷胱甘肽(GSH)含量也显著提高。(3)叶片类黄酮、总酚和原花青素的含量在一定的胁迫时间范围内亦显著增加,并伴随着活性氧成分O_2~(-·)产生速率和H_2O_2水平降低。研究认为,外源H2S能通过促进干旱胁迫下白三叶体内的多重抗氧化防御能力来提高其幼苗的抗旱性。     

Comparative Proteomic Analysis of Differentially Expressed Proteins Induced by Hydrogen Sulfide in Spinacia oleracea Leaves

Hydrogen sulfide (H₂S), as a potential gaseous messenger molecule, has been suggested to play important roles in a wide range of physiological processes in plants. The aim of present study was to investigate which set of proteins is involved in H₂S-regulated metabolism or signaling pathways. Spinacia oleracea seedlings were treated with 100 µM NaHS, a donor of H₂S. Changes in protein expression profiles were analyzed by 2-D gel electrophoresis coupled with MALDI-TOF MS. Over 1000 protein spots were reproducibly resolved, of which the abundance of 92 spots was changed by at least 2-fold (sixty-five were up-regulated, whereas 27 were down-regulated). These proteins were functionally divided into 9 groups, including energy production and photosynthesis, cell rescue, development and cell defense, substance metabolism, protein synthesis and folding, cellular signal transduction. Further, we found that these proteins were mainly localized in cell wall, plasma membrane, chloroplast, mitochondria, nucleus, peroxisome and cytosol. Our results demonstrate that H₂S is involved in various cellular and physiological activities and has a distinct influence on photosynthesis, cell defense and cellular signal transduction in S. oleracea leaves. These findings provide new insights into proteomic responses in plants under physiological levels of H₂S.     

iTRAQ‐based quantitative proteomic analysis reveals new metabolic pathways of wheat seedling growth under hydrogen peroxide stress

As an abundant ROS, hydrogen peroxide (H₂O₂) plays pivotal roles in plant growth and development. In this work, we conducted for the first time an iTRAQ‐based quantitative proteomic analysis of wheat seedling growth under different exogenous H₂O₂ treatments. The growth of seedlings and roots was significantly restrained by increased H₂O₂ concentration stress. Malondialdehyde, soluble sugar, and proline contents as well as peroxidase activity increased with increasing H₂O₂ levels. A total of 3 425 proteins were identified by iTRAQ, of which 157 showed differential expression and 44 were newly identified H₂O₂‐responsive proteins. H₂O₂‐responsive proteins were mainly involved in stress/defense/detoxification, signal transduction, and carbohydrate metabolism. It is clear that up‐regulated expression of signal transduction and stress/defence/detoxification‐related proteins under H₂O₂ stress, such as plasma membrane intrinsic protein 1, fasciclin‐like arabinogalactan protein, and superoxide dismutase, could contribute to H₂O₂ tolerance of wheat seedlings. Increased gluconeogenesis (phosphoenol‐pyruvate carboxykinase) and decreased pyruvate kinase proteins are potentially related to the higher H₂O₂ tolerance of wheat seedlings. A metabolic pathway of wheat seedling growth under H₂O₂ stress is presented.     

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), endogenous H₂S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.     

Hydrogen sulfide promotes wheat seed germination under osmotic stress

Effects of NaHS, H₂S donor, on germination and antioxidant metabolism in wheat (Triticum aestivum L.) seeds under osmotic stress were investigated. With the enhancement of osmotic stress, which was mimicked by PEG-6000, the seed germination dropped gradually. NaHS treatment could promote wheat seed germination against osmotic stress in a dose-dependent manner; while Na⁺ and other sulfur-containing components, such as S²⁻, SO₄²⁻, SO₃²⁻, HSO₄⁻ and HSO₃⁻, were not able to improve seed germination as NaHS did, confirming H₂S or HS⁻ derived from NaHS contribute to the protective roles. Further experiments showed that NaHS treatment combined with PEG enhanced the activities of amylase and esterase in comparison to PEG treatment alone. Alternatively, NaHS treatment significantly reduced malondialdehyde and hydrogen peroxide accumulation in seeds. Significant enhancement of catalase and ascorbate peroxidase activities and decrease in lipoxygenase activity were observed in NaHS treated seeds, while peroxidase and superoxide dismutase activities were not affected as compared with the control. Furthermore, the H₂S donor treatment could retain higher levels of endogenous H₂S in wheat seeds under osmotic stress. These data indicated that H₂S played a protective role in wheat seed against osmotic stress.     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Hydrogen sulfide alleviates aluminum toxicity in barley seedlings

Aims

Aluminum (Al) toxicity is one of the major factors that limit plant growth. Low concentration of hydrogen sulfide (H₂S) has been proven to function in physiological responses to various stresses. The objective of this study is to investigate the possible role of H₂S in Al toxicity in barley (Hordeum vulgare L) seedlings.

Methods

Barley seedlings pre-treated with sodium hydrosulfide (NaHS), a H₂S donor, and subsequently exposed to Al treatment were studied for their effects on root elongation, Al accumulation in seedlings, Al-induced citrate secretion and oxidative stress, and plasma membrane (PM) H⁺-ATPase expression.

Results

Our results showed that H₂S had significant rescue effects on Al-induced inhibition of root elongation which was correlated well with the decrease of Al accumulation in seedlings. Meanwhile, Al-induced citrate secretion was also significantly enhanced by NaHS pretreatment. Al-induced oxidative stress as indicated by lipid peroxidation and reactive oxygen species burst was alleviated by H₂S through the activation of the antioxidant system. Moreover, Al-induced reduction in PM H⁺-ATPase expression was reversed by exogenous NaHS.

Conclusions

Altogether, our results suggest H₂S plays an ameliorative role in protecting plants against Al toxicity by inducing the activities of antioxidant enzymes, increasing citrate secretion and citrate transporter gene expression, and enhancing the expression of PM H⁺-ATPase.     

外源H_2S对NO_3~-胁迫下番茄幼苗生理生化特性的影响

采用营养液水培方法,通过外源施加H2S供体NaHS(100μmol/L),研究了信号分子H2S对100mmol/L NO3-胁迫下番茄幼苗生理生化特性的影响。结果表明:(1)NO3-胁迫下,随着处理时间的延长,番茄幼苗的株高、根长、鲜重和干重显著降低,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著降低,而胞间CO2浓度以及丙二醛(MDA)、H2O2含量增加,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)活性显著降低,抗坏血酸(AsA)和还原性谷胱甘肽(GSH)含量显著降低。(2)与NO3-胁迫处理相比,外源NaHS处理1、3、5d后,番茄幼苗的株高、根长、鲜重和干重显著增加,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著升高,而胞间CO2浓度显著降低;MDA和H2O2含量降低,SOD、POD、CAT和APX活性显著增强,AsA和GSH含量显著增加,而且幼苗的硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶的活性显著增强;L-半胱氨酸脱巯基酶活性和内源H2S含量增加。研究认为,外源H2S可能通过提高抗氧化物酶的活性和增加抗氧化物质含量来缓解NO3-对番茄幼苗造成的伤害,从而增强其对NO3-胁迫耐性。     

Hydrogen sulfide protects soybean seedlings against drought-induced oxidative stress

Increasing evidence indicates that hydrogen sulfide (H₂S) is the third “gas signal molecule” after NO and CO in animal. In the present study, we found that soybean (Glycine max L.) seedlings sprayed with exogenous H₂S donor NaHS prolonged the longer survival time of life, and enlarged higher biomass of both leaf and root than in non-sprayed controls under continuous drought stress. With the continuous drought stress, the content of chlorophyll in the leaves of both Xu-1 and Xu-6 cultivar of soybean decreased dramatically. The drought-induced decrease in chlorophyll could be alleviated by spraying H₂S donor. It was also shown that spraying with H₂S donor dramatically retained higher activities of superoxide dismutase (SOD, EC 1.1.5.1.1), catalase (CAT, EC1.11.1.6) and lower activity of lipoxygenases (LOX, EC 1.13.11.12), delayed excessive accumulation of malondialdehyde, hydrogen peroxide, and superoxide anion (O₂^·−) compared with the control. These results suggest that H₂S can increase drought tolerance in soybean seedlings by acting as an antioxidant signal molecule for the response.     

Photosynthetic CO<Subscript>2</Subscript>/H<Subscript>2</Subscript>O gas exchange and dynamics of carbohydrates content in maize leaves under drought

We studied the temporal sequence of changes in the photosynthetic CO₂/H₂O gas exchange intensity, as well as leaf water status, contents of soluble carbohydrates, starch, proline, pigments, and MDA, in maize seedlings (Zea mays L., cv. Luchistaya) under adaptation to increasing water deficit. The duration of drought was 2, 3, 5, and 6 days. Withholding water from maize plants caused gradual increase in the intensity of water deficit: from mild (2 or 3 days) to moderate (5 days) and nearly severe (6 days) water stress. After 6 days, relative leaf water content decreased by 19.8% as compared to the control. On the second day after the onset of drought, slight reduction in the photosynthetic CO₂/H₂O gas exchange intensity of the treated plants was observed. After 6 days, photosynthesis and transpiration of leaves synchronously reduced almost threefold due to stomatal closure. The progressive soil drought had substantial impact on the carbohydrate metabolism. After 2 days of water deficit, the content of reducing sugars and sucrose increased slightly, whereas after 6 days, it increased ten and four times, respectively. After 2, 3, and 5 days of drought, the starch content declined slightly; however, under severe drought (6 days), it increased by 30% as compared to the control. Simultaneously with the increase in the content of soluble sugars, proline content increased significantly and it was the highest on the sixth day of drought. At all stages of water deficit, the proline content increased more significantly than the content of reducing carbohydrates and sucrose. Under increasing water deficit (5 and 6 days), the content of MDA was found to rise. At the initial drought stage (2 or 3 days) and under severe water deficit (6 days), no significant changes in the pigment content were observed. Thus, at the initial stages of progressive drought, in the leaves of this maize cultivar, a decline in photosynthetic activity proceeded simultaneously with accumulation of reducing sugars, sucrose, and proline. The results obtained showed that, at the first stages of adaptation of maize seedlings to drought, the changes in carbohydrate and proline metabolism have been observed, which have increased upon further plant dehydration.     

Protective effect of hydrogen sulfide against stress-induced lung injury: involvement of Nrf2, NFκB/iNOS,and HIF-1α signaling pathways

Stress is a common phenomenon that is attracting increasing attention. Hydrogen sulfide (H₂S) is a gasotransmitter that plays an important role in many physiological and pathological events. Our study aimed to estimate the effect and the underlying mechanisms of the H₂S donor, sodium hydrosulfide (NaHS), against immobilization stress (IS)–induced lung injury. Forty adult male rats were classified into control group, NaHS group, and IS groups with and without NaHS treatment. Serum was obtained to determine corticosterone (CORT), total antioxidant capacity (TAC), tumor necrosis factor‐α (TNF‐α), and interleukin-10 (IL-10) levels. Lung H₂S, nitric oxide (NO), inducible nitric oxide synthase (iNOS), and malondialdehyde (MDA) levels were measured. Lung expressions of H₂S synthesizing enzymes and Western blot analysis of nuclear factor erythroid 2–related factor 2 (Nrf2) and hypoxia-inducible factor 1 alpha (HIF 1α) were estimated. Histopathological changes and immunohistochemical assessment of nuclear factor kappa B (NF-κB) and caspase‐3 were also done. Pretreatment with NaHS led to marked histological protection from lung damage seen in IS rats. Furthermore, pretreatment with NaHS before IS protected lung H₂S levels and expressions of H₂S-synthesizing enzymes. Similarly, the levels of CORT, TNF-α, IL-10, MDA, TAC, NO, iNOS, HIF-1 α, and nuclear Nrf2 and expressions of NF-kB and caspase 3 were all maintained at near control levels in contrast to that in the IS rats. In conclusion, NaHS is protective against stress‐induced lung injury due to its antioxidant, anti-inflammatory, anti-fibrotic, and antiapoptotic effects. Thus, NaHS can be used to minimize stress complications on lung.     

Pre-treatment with H<Subscript>2</Subscript>O<Subscript>2</Subscript> induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 μM H₂O₂ for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H₂O₂ alone had no effect on the proline, malondialdehyde (MDA) and H₂O₂ contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 μM H₂O₂ treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H₂O₂ pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of ¹⁴CO₂ fixation was higher and MDA, H₂O₂ and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl⁻ content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H₂O₂ metabolism is involved as a signal in the processes of barley salt tolerance.     

Signaling molecule methylglyoxal-induced thermotolerance is partly mediated by hydrogen sulfide in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) seedlings

Methylglyoxal (MG) was traditionally viewed as toxic by-product of glycolysis and photosynthesis in plants, but now is emerging as a signaling molecule, which, similar to hydrogen sulfide (H₂S), participates in regulating seed germination, growth, development, and response to abiotic stress. However, whether exists an mutual effect between MG and H₂S in improving thermotolerance in plants is not found to be reported. In this paper, interplay between MG and H₂S in the formation of thermotolerance in maize seedlings was investigated. The results indicated that MG pretreatment elevated the survival percentage of maize seedlings under high-temperature stress, manifesting that MG could boost the thermotolerance of maize seedlings. Interestingly, MG-induced thermotolerance was reinforced by sodium hydrosulphide (NaHS, H₂S donor), while impaired by dl-propargylglycine (inhibitor of H₂S biosynthesis) and hypotaurine (scavenger of H₂S), respectively. In addition, H₂S could induce the thermotolerance of maize seedlings, which was impaired by aminoguanidine (AG) and N-acetyl-l-cysteine (NAC) (MG scavengers), respectively. Furthermore, MG stimulated the activity of a key enzyme in H₂S biosynthesis, l-cysteine desulfhydrase, which, in turn, triggered the elevation of endogenous H₂S in maize seedlings. In addition, H₂S increased the level of endogenous MG; this increase was crippled by AG and NAC. This paper, for the first time, reported that MG could improve the thermotolerance of maize seedlings, and its acquisition was, at least partly, mediated by H₂S.     

Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression

Hydrogen sulfide (H₂S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H₂S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H₂S production, and thereafter PCD occurred. Exogenous H₂S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H₂S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H₂S scavenger, suggesting that this effect of NaHS was in an H₂S-dependent fashion. Further experiment confirmed that H₂S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H₂S-delayed PCD in GA-treated wheat aleurone cells was associated with the modulation of GSH homeostasis and HO-1 gene expression.     

Hydrogen sulphide may be a novel downstream signal molecule in nitric oxide‐induced heat tolerance of maize (Zea mays L.) seedlings

Nitric oxide (NO) is a second messenger with multifunction that is involved in plant growth, development and the acquisition of stress tolerance. In recent years, hydrogen sulphide (H₂S) has been found to have similar functions, but crosstalk between NO and H₂S in the acquisition of heat tolerance is not clear. In this study, pretreatment with the NO donor sodium nitroprusside (SNP) improved the survival percentage of maize seedlings and alleviated an increase in electrolyte leakage and a decrease in tissue vitality as well as accumulation of malondialdehyde, indicating that pretreatment with SNP improved the heat tolerance of maize seedlings. In addition, pretreatment with SNP enhanced the activity of L‐cystine desulfhydrase, which, in turn, induced accumulation of endogenous H₂S, while application of H₂S donors, NaHS and GYY4137, increased endogenous H₂S content, followed by mitigating increase in electrolyte leakage and enhanced survival percentage of seedlings under heat stress. Interestingly, SNP‐induced heat tolerance was enhanced by application of NaHS and GYY4137, but was eliminated by inhibitors of H₂S synthesis DL‐propargylglycine, aminooxyacetic acid, potassium pyruvate and hydroxylamine, and the H₂S scavenger hypotaurine. All of the above‐mentioned results suggest that SNP pretreatment could improve heat tolerance, and H₂S may be a downstream signal molecule in NO‐induced heat tolerance of maize seedlings.     

Ascorbate-glutathione metabolism during PEG-induced water deficit in <Emphasis Type="Italic">Trifolium repens</Emphasis>

In order to elucidate the response of the ascorbate-glutathione (ASC-GSH) cycle to drought stress, the activities of antioxidant enzymes and the levels of molecules involved in the ASC-GSH metabolism were studied in Trifolium repens L. seedlings subjected to PEG-induced water deficit. Compared to the control, the contents of H₂O₂, thiobarbituric acid reactive substances (TBARS), ascorbate (ASC), dehydroascorbate (DHA), and glutathione disulfide (GSSG) increased in PEG-treated seedlings, whereas the glutathione (GSH) content kept constant during the drought period. Further more, the ASC/DHA and GSH/GSSG ratios decreased in the presence of PEG. Except for that of monodehydroascorbate reductase (MDHAR), the activities of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were up-regulated during water deficit, and the increases in APX and DHAR activities were much higher than those in GR activity. These data indicate that fluctuations in the ASC-GSH metabolism resulted from PEG treatment may have a positive effect on drought stress mitigation in T. repens.     

Physiological responses of wheat seedlings to drought and UV-B radiation. Effect of exogenous sodium nitroprusside application

Physiological and biochemical responses of wheat seedlings to drought, UV-B radiation, and combined stress were investigated. Drought, UV-B, and combined stresses retarded seedling growth by 26.5, 29.1, and 55.9%, respectively. One reason for growth retardation may be the oxidative damage indicated by an increase in the H₂O₂ content and lipid peroxidation degree. Furthermore, there was negative correlation between shoot fresh weight and H₂O₂ content, fresh weight and the content of thiobarbituric acid-reacting substances (TBARS), and the positive correlation between H₂O₂ content and TBARS (R ² = 0.9251, 0.9005, and 0.9007, respectively). The activities of superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase increased under drought, UV-B, and the combination of stresses, while catalase activity decreased under the combined stress as compared to the control. The combination of drought and UV-B caused more severe damage to wheat seedlings than stress factors applied separately. Thus, the combined application of drought and UV-B had more strong adverse effects on wheat seedlings. The addition of 0.2 mM sodium nitroprusside (SNP) enhanced wheat seedling growth under drought, UV-B, and combined stress, likely, due to decreasing the accumulation of H₂O₂ and lipid peroxidation as well as activating the antioxidant enzymes. However, SNP treatment decreased the proline content. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 5, pp. 763–769. The text was submitted by the authors in English.