Thiol accumulation and cysteine desulfhydrase activity in H2S-fumigated leaves and leaf homogenates of cucurbit plants

Fumigation of both, cucurbit plants and cucurbit leaf homogenates with hydrogen sulfide (H2S) resulted in an increase in soluble thiol, mainly glutathione and cysteine. In leaf homogenates this increase was counteracted or prevented by the addition at 1 mM of inhibitors of pyridoxalphosphate dependent enzymes or of products of the cysteine desulfhydrase reaction. These compounds inhibited cysteine desulfhydrase activity, but did not severely affect O-acetylserine sulfhydrylase activity at this concentration. These results provide circumstantial evidence that cysteine desulfhydrase in its reverse reaction, but not O-acetylserine sulfhydrylase participates in the assimilation of atmospheric H2S.