With the enhancement of copper (Cu) stress, the germination percentage of wheat seeds decreased gradually. Pretreatment with sodium hydrosulfide (NaHS), hydrogen sulfide (H(2)S) donor alleviated the inhibitory effect of Cu stress in a dose-dependent manner; whereas little visible symptom was observed in germinating seeds and radicle tips cultured in NaHS solutions. It was verified that H(2)S or HS(-) rather than other sulfur-containing components derived from NaHS attribute to the potential role in promoting seed germination against Cu stress. Further studies showed that NaHS could promote amylase and esterase activities, reduce Cu-induced disturbance of plasma membrane integrity in the radicle tips, and sustain lower levels of malondialdehyde and H(2)O(2) in germinating seeds. Furthermore, NaHS pretreatment increased activities of superoxide dismutase and catalase and decreased that of lipoxygenase, but showed no significant effect on ascorbate peroxidase. Alternatively, NaHS prevented uptake of Cu and promoted the accumulation of free amino acids in seeds exposed to Cu. In addition, a rapid accumulation of endogenous H(2)S in seeds was observed at the early stage of germination, and higher level of H(2)S in NaHS-pretreated seeds. These data indicated that H(2)S was involved in the mechanism of germinating seeds' responses to Cu stress.

In this paper, effect of NaHS, a hydrogen sulfide (H 2 S) donor on chlorophyll and antioxidant metabolism in seedling leaves of sweetpotato under osmotic stress was investigated. With the enhancement of osmotic stress, which was mimicked by PEG-6000, chlorophyll in seedling leaves of sweetpotato (Ipomoea batatas) decreased dramatically. At 15% PEG (w/v), chlorophyll concentration reached only 50% compared with that of the controls. The osmotic-induced decrease in chlorophyll concentration could be alleviated by spraying exogenous H 2 S donor, NaHS in a dose-dependent manner, while little visible symptoms were observed in leaves sprayed with NaHS under control conditions. It was also shown that H 2 S or HS -rather than other sulfur-containing components derived from NaHS contributed to the protective role against chlorophyll degradation during osmotic stress. Further studies showed that NaHS spraying dramatically promoted the activities of superoxide dismutase, catalase, ascorbate peroxidase and decreased that of lipoxygenase and the concentrations of hydrogen peroxide (H 2 O 2 ) and malondialdehyde. In addition, concentrations of endogenous H 2 S in NaHS-sprayed seedlings were higher than that in water-spraying control under osmotic stress. These data indicated that H 2 S plays a protective role in sweetpotato seedlings during osmotic stress.

Protective role of hydrogen sulfide (H 2 S) on seed germination and seedling growth was studied in wheat (Triticum) seeds subjected to aluminum (Al 3+ ) stress. We show that germination and seedling growth of wheat is inhibited by high concentrations of AlCl 3 . At 30 mmol/L AlCl 3 germination is reduced by about 50% and seedling growth is more dramatically inhibited by this treatment. Pre-incubation of wheat seeds in the H 2 S donor NaHS alleviates AlCl 3 -induced stress in a dose-dependant manner at an optimal concentration of 0.3 mmol/L. We verified that the role of NaHS in alleviating Al 3+ stress could be attributed to H 2 S/HS − by showing that the level of endogenous H 2 S increased following NaHS treatment. Furthermore, other sodium salts containing sulfur were ineffective in alleviating Al 3+ stress. NaHS pretreatment significantly increased the activities of amylases and esterases and sustained much lower levels of MDA and H 2 O 2 in germinating seeds under Al 3+ stress. Moreover, NaHS pretreatment increased the activities of guaiacol peroxidase, ascorbate peroxidase, superoxide dismutase and catalase and decreased that of lipoxygenase. NaHS pretreatment also decreased the uptake of Al 3+ in AlCl 3 -treated seed. Taken together these results suggest that H 2 S could increase antioxidant capability in wheat seeds leading to the alleviation of Al 3+ stress.Zhang H, Tan ZQ, Hu LY, Wang SH, Luo JP, Jones RL (2010) Hydrogen sulfide alleviates aluminum toxicity in germinating wheat seedlings.

Increasing evidence indicates that hydrogen sulfide (H 2 S) 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 H 2 S 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 H 2 S donor. It was also shown that spraying with H 2

Aluminum-induced exudation of organic acids from roots has been proposed as a mechanism for Al tolerance in plants. To better understand the regulatory process leading to efflux of organic acids, the possible involvement of salicylic acid (SA) in regulating Alinduced citrate release in Cassia tora L. was identified. The response of citrate efflux to exogenous SA was concentration-dependent. Application of SA at 5 lM in solution containing 20 lM Al increased citrate efflux to levels 1.76-fold higher than in controls (20 lM Al alone). However, inhibition of citrate release was observed when SA concentrations increased to more than 20 lM. Increased citrate efflux due to the SA treatment was associated with decreased inhibition of root growth and Al content in root tips, suggesting that exogenous SA could confer Al tolerance by increasing citrate efflux. We also examined citrate synthase activities (EC 4.1.3.7) and citrate concentrations in root tips exposed to Al and/or SA. However, both citrate synthase activities and citrate accumulation remained unaffected. These results indicate that SA-promotion of Al-induced citrate efflux is not correlated with increase in citrate production. Total endogenous SA concentrations were measured in root tips and the SA concentrations were significantly enhanced by Al at levels of 10-50 lM.