Role of O-Acetylserine in Hydrogen Sulfide Emission from Pumpkin Leaves in Response to Sulfate

Abstract

In the presence of excess sulfate, cysteine synthesis in pumpkin leaves is not limited by sulfate reduction but by the availability of O-acetylserine. Feeding of O-acetylserine or its metabolic precursors S-acetyl-CoA and CoA to leaf discs enhanced the incorporation of [35S]sulfate into reduced S compounds, mainly into cysteine, at the cost of lowered H2S emission; the uptake and reduction of sulfate is not affected by these treatments. .beta.-Fluoropyruvate, an inhibitor of the generation of S-acetyl-coenzyme A via pyruvate dehydrogenase, stimulated H2S emission in response to sulfate. This stimulation is overcompensated by addition of O-acetylserine, S-acetyl-CoA or CoA. Apparently in the presence of high amounts of sulfate, excess S is reduced and emitted as H2S into the atmosphere. The H2S emitted seems to be produced by the liberation from a precursor of cysteine rather than by cysteine desulfhydration.