Effects of Atmospheric H2S on Thiol Composition of Crop Plants

Exposure of crop plants to H2S resulted in an increase in thiol level and a change in the composition of the thiol pool. Non-leguminous species accumulated cysteine and glutathione in the light, whereas in the dark, substantial amounts of gamma-glutamyl-cysteine were also detected. In leguminous species, which contain homoglutathione instead of glutathione, the level of cysteine, gamma-glutamyl-cysteine and homoglutathione increased, both in the light and in the dark. In clover, a species that contains glutathione and homoglutathione, both thiols increased to a high level. Feeding beta-alanine to detached shoots of soybean strongly reduced the accumulation of gamma-glutamyl-cysteine. This suggests that in legumes, the accumulation of gamma-glutamyl-cysteine upon exposure to H2S may result from a limited availability of substrate for homoglutathione synthesis.