Necessity of Superoxide Production for Development of Etiolated Wheat Seedlings

Abstract

It was found that production of superoxide (O₂ ^{– ·}) is crucial for normal morphogenesis of etiolated wheat seedlings in the early stages of plant development. The development of etiolated wheat seedlings was shown to be accompanied with cyclic changes in the rate of O₂ ^{– ·} production both in the entire intact seedling and in its separated organs (leaf, coleoptile). First increase in the rate of O₂ ^{– ·} production was clearly observed in the period from two to four days of seedling development, then the rate of O₂ ^{– ·} production decreased to the initial level, and then it increased again for two days to a new maximum. An increase in O₂ ^{– ·} production in the period of the first four days of seedling development correlates with an increase in DNA and protein contents in the coleoptile. The second peak of increased rate of O₂ ^{– ·} production observed on the sixth or seventh day of seedling development coincides with a decrease in DNA and protein contents and apoptotic internucleosomal nuclear DNA fragmentation in the coleoptile. Incubation of seedlings in the presence of the antioxidant BHT (ionol) strongly affects their development but it does not influence the increase in DNA and protein contents for the initial four days of seedling life, and it slows down the subsequent age-dependent decrease in protein content and fully prevents the age-dependent decrease in DNA content in the coleoptile. A decrease in the O₂ ^{– ·} amount induced by BHT distorts the seedling development. BHT retards seedling growth, presumably by suppression of cell elongation, and it increases the life span of the coleoptile. It seems that O₂ ^{– ·} controls plant growth by cell elongation at the early stages of seedling development but later O₂ ^{– ·} controls (induces) apoptotic DNA fragmentation and protein disintegration.