Effects of light and atmospheric H2S on amino acid composition in spinach leaves

The effect of fumigation with 0.25 mul l(-1) H2S on changes in the composit ion of the free amino acid pool showed a consistent decrease in serine, pre cursor for cysteine synthesis, in the light and to a lesser extent in the d ark. Comparison of the serine data with data on thiol level, from experimen ts performed under the same experimental conditions, shows that the decreas e in serine is of the same order of magnitude as the increase in thiols ove r the same period. This suggests that the decline in serine level when plan ts are fumigated with H2S is the result of a drain of serine for thiol synt hesis.