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.