Atmospheric H2S as sulphur source for Brassica oleracea:: Consequences for the activity of the enzymes of the assimilatory sulphate reduction pathway

Short-term exposure of Brassica oleracea L. (curly kale) to atmospheric H2S levels (0.2-0.8 muL .L-1), which an sufficient to meet the plants sulphur requirement, resulted in a decrease in the activity of adenosine 5'-phosphosulphate reductase (APR) in the shoot. The reduction in APR activity was maximally 80 % and was already substantial after id exposure to 0.2 muL .L-1 H2S. The activity of APR in the roots remained unaffected upon exposure to all levels of H2S. The activities of ATP-sulphurylase (ATPS), serine acetyltransferase (SAT) and O-acetylserine(thiol)lyase (OAS-TL), in both shoot and roots were not affected upon exposure to H2S levels ranging from 0.2-0.8 muL .L-1. There was a rapid increase in the shoot thiol content, including cysteine, upon H2S exposure and a maximal 3-fold increase in thiol content occurred after 5 h exposure. In the roots, the thiol content was only slightly increased after 2 d H2S exposure. The relationship between the pattern of thiol accumulation and changes in sulphate assimilation upon H2S exposure is discussed. (C) 2001 Editions scientifiques et medicales Elsevier SAS.