Ascorbate-dependent hydrogen peroxide detoxification and ascorbate regeneration during germination of a highly productive maize hybrid: Evidence of an improved detoxification mechanism against reactive oxygen species

Ascorbate content and the activities of some key enzymes involved in the detoxification from reactive oxygen species were investigated in germinated embryos of two Zea mays L, inbred lines (B73 and Mo17) and of their heterotic F1 hybrid (B73 x Mo17). The F1 hybrid showed a higher ascorbate biosynthetic capability owing to a higher activity of L-galactono-gamma-lactone dehydrogenase (EC 1,6,5,4), the last enzyme in ascorbate biosynthesis. Ascorbate peroxidase (EC 1,11.1,11), ascorbate free radical reductase (EC 1.6.5.4) and dehydroascorbate reductase (EC 1.8.5.1) activities were much higher in the F1 hybrid than in either inbred line, whereas catalase (EC 1.11.1.6) activity was similar in the three genotypes, Native polyacrylamide gel electrophoresis (PAGE) analysis showed three forms of cytosolic ascorbate peroxidase, both in parental lines and in the FI hybrid. On the other hand, a complex pattern of proteins with dehydroascorbate reductase activity was observed, with the hybrid combining the different dehydroascorbate-reducing proteins expressed by the inbred lines. The possible involvement of the enzymes of the ascorbate system in the phenomenon of hybrid vigour is discussed.