Changes in Paramagnetic Manganese (Mn(II)) and Related Enzyme Activities in Isolated Cucumber Cotyledons During Growth

Abstract

Changes» in the activities of IAA oxidase, peroxidase, and ascorbic acid utilization (AAU) and in the level of paramagnetic manganese (Mn(II)) have been studied during GA3-induced growth of the isolated cucumber cotyledons in light or dark. In dark-grown cotyledons, where GA3 fails to evoke any growth response, an initial decline in the Mn(II) content during the first 8 h is followed by a rise which approaches the control value between 12 and 24 h. A marked, almost linear increase is observed in Mn(II) levels from 48 h onwards. The initial decline in Mn(II) is accompanied by an increase in IAA oxidase activity and decreased AAU. The large increases obtained at later times, viz. 48 and 72 h, appear to be related primarily to the release of manganese due to the degradation of protein bodies which proceeds under the action of GA and also to increased AAU. The IAA oxidase and peroxidase activities are close to control during this period. In light, however, IAA oxidase and peroxidase activities show marked increase during the first 4 h but no significant changes are observed in Mn(II) level or AAU. The peak of Mn(II) observed at 8 h corresponds with lower activities of IAA oxidase and peroxidase but an increase in AAU. The changes in Mn(II) closely correspond with the changes in AAU in light, peroxidase and IAA oxidase activities keeping close to the control. It appears that GA action is related to increased Mn(II) due to increased AAU which may be coupled to the peroxidase-IAA oxidase system. The study confirms the postulate given by us in an earlier paper.