Necessity of superoxide production for development of etiolated wheat seedlings

It was found that production of superoxide (Of) is crucial for normal morph ogenesis of etiotated wheat seedlings in the early stages of plant developm ent. The development of etiolated wheat seedlings was shown to be accompani ed with cyclic changes in the rate of O-2(.) production both in the entire intact seedling and in its separated organs (leaf, coleoptile). First incre ase in the rate of O-2(.) production was clearly observed in the period fro m two to four days of seedling development, then the rate of Of production decreased to the initial level, and then it increased again for two days to a new maximum. An increase in O-2(.) production in the period of the first four days of seedling development correlates with an increase in DNA and p rotein contents in the coleoptile. The second peak of increased rate of O-2 (.) production observed on the sixth or seventh day of seedling development coincides with a decrease in DNA and protein contents and apoptotic intern ucleosomal nuclear DNA fragmentation in the coleoptile. Incubation of seedl ings in the presence of the antioxidant BHT (ionol) strongly affects their development but it does not influence the increase in DNA and protein conte nts for the initial four days of seedling life, and it slows down the subse quent age-dependent decrease in protein content and fully prevents the age- dependent decrease in DNA content in the coleoptile. A decrease in the of a mount induced by BHT distorts the seedling development. BHT retards seedlin g growth, presumably by suppression of cell elongation, and it increases th e life span of the coleoptile. It seems that ; controls plant growth by cel l elongation at the early stages of seedling development but later O-2(.) c ontrols (induces) apoptotic DNA fragmentation and protein disintegration.