Effect of Benzyladenine on Some Enzymes of Mitochondria and Microbodies in Excised Sunflower Cotyledons

Benzyladenine (BA) increases the rate of expansion of dark-grown sunflower (Helianthus annuus L.) cotyledons. The hormone slightly enhances the development of the two glyoxysomal enzymes, isocitrate lyase and malate synthetase, during the first 3 days of germination and greatly accelerates their decay in the 2 following days. The levels of the peroxisomal enzymes, glycolate oxidase and glyoxylate reductase, are enhanced by BA more than those of the two glyoxysomal enzymes. These effects of BA on microbody enzymes are very similar to those of white light. Mitochondrial enzyme activities are increased to a varying extent by BA: the increase is minimal for fumarase, and maximal for cytochrome oxidase. The level of cytochrome oxidase is enhanced 346% at the 5th day of germination. Also, the rate of O(2) consumption is increased by BA, but the time course of this increased O(2) consumption does not match with that of cytochrome oxidase. Fusicoccin, a fungal toxin, mimics the effect of BA on cotyledon expansion, but fails to duplicate its action on microbody enzymes. This suggests that the effect of BA on microbody enzymes is not closely linked with the mechanism of growth promotion.