Atmospheric H 2S as sulphur source for Brassica oleracea: Consequences for the activity of the enzymes of the assimilatory sulphate reduction pathway

Abstract

Short-term exposure of Brassica oleracea L. (curly kale) to atmospheric H 2S levels (0.2–0.8 μL·L –1), which are 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 1 d exposure to 0.2 μL·L –1 H 2S. The activity of APR in the roots remained unaffected upon exposure to all levels of H 2S. 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 H 2S levels ranging from 0.2–0.8 μL·L –1. There was a rapid increase in the shoot thiol content, including cysteine, upon H 2S 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 H 2S exposure. The relationship between the pattern of thiol accumulation and changes in sulphate assimilation upon H 2S exposure is discussed.