Changes in the Activities of IAA Oxidase, Peroxidase, Ascorbic Acid Utilization and in the Endogenous Level of Paramagnetic Mn++ during Benzyladenine-induced Growth of Excised Cucumber Cotyledons

Abstract

Changes in the activities of IAA oxidase, peroxidase, ascorbic acid utilization (AAU) and in the level of paramagnetic Mn++ have been studied during benzyl adenine (BA)-induced growth of excised cucumber cotyledons in the light and in darkness. BA exerts an inhibitory effect on the activities of IAA oxidase, peroxidase and AAU at early times of treatment, the effect being more marked in darkness. Light seems to help recover from the inhibitory effect of BA on the activities measured. Enhancement in the activities of IAA oxidase, peroxidase and AAU at later times suggests that this may not be a direct action of BA but may be due to some secondary reaction triggered by BA or its metabolic products. This also shows that cotyledon expansion is a phasic process. with respect to the activities measured. Changes in peroxidase activity show close parallelism with changes in the activities of IAA oxidase and AAU suggesting the role of peroxidase in their oxidation. Changes in peroxidase activity show an inverse correlation with the changes in the level of endogenous Mn++ in BA-treated cotyledons in the light. The absence of similar correlation in BA-treated cotyledons in darkness is primarily due to the absence of chloroplasts and secondly may be due to a paucity of phenolic substances which are largely synthesised in the light. In absence of these phenolic donors peroxidase would be unable to oxidize Mn++. This suggests that the shift in the balance of hormones congenial for BA-induced growth is brought about directly by peroxidase which may be independent of endogenous manganese.