Developmental changes of catalase and superoxide dismutase isoenzymes in zygotic and somatic embryos of horse chestnut

Catalase (CAT) and superoxide dismutase (SOD), two of the major antioxidant enzyme systems, were examined by native PAGE at different stages of zygotic and somatic embryogenesis of horse chestnut (Aesculus hippocastanum L.). During both zygotic and somatic embryogenesis, CAT and SOD specific activities increased, but electrophoretic analysis revealed remarkable differences in the isoenzyme patterns. Two CAT isoforms were differentially present during zygotic embryogenesis. The transition from the fast to the slow migrating form occurred in July, approximately 2 months after pollination. In contrast to zygotic, the two isoforms were continuously detectable during somatic embryogenesis. In fact, with the exception of the callus stage, in which only one form was present, both of the CAT isoforms are equally active during the somatic embryo development. Unlike CAT, all SOD isoenzymes, one Mn-SOD and five Cu/Zn-SODs, were present during all the stages of zygotic embryo formation, but only Mn-SOD and an Fe-SOD were detected during somatic embryogenesis. These results suggest the occurrence of oxidative stress conditions during in vitro culture which, in horse chestnut, could account for the difficulties observed in the development of the somatic embryo into a plantlet.