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
embryo-genesis. 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.