Intercellular localization of cysteine synthase and alliinase in bundle sheaths of Allium plants

Abstract

Cysteine synthase and alliinase (alliin-lyase) are terminal enzymes responsible for synthesis of cysteine and degradation of alliin (S-alk(en)yl-cysteine sulfoxide), respectively, in Allium plants. We determined the intercellular localization of cysteine synthase and alliinase using antibodies against these proteins. Cysteine synthase was predominantly localized in bundle sheath and phloem cells of three Allium plants, A. tuberosum, A. cepa and A. sativum. Lower amounts could be detected in mesophyll cells. Alliinase was almost exclusively localized in bundle sheath cells of the three Allium species. These results suggest the importance of bundle sheath cells for both synthesis and degradation of sulfurcontaining compounds in Allium. plants.