Changes in Paramagnetic Manganese (Mn(II)) and Related Enzyme Activities in Isolated Cucumber Cotyledons During Growth: I. EFFECT OF GIBBERELLIC ACID

Changes in the activities of IAA oxidase, peroxidase, and ascorbicacid utilization (AAU) and in the level of paramagnetic manganese(Mn(II)) have been studied during GA₃-induced growth of theisolated cucumber cotyledons in light or dark. In dark-growncotyledons, where GA₃ fails to evoke any growth response, aninitial decline in the Mn(II) content during the first 8 h isfollowed by a rise which approaches the control value between12 and 24 h. A marked, almost linear increase is observed inMn(II) levels from 48 h onwards. The initial decline in Mn(II)is accompanied by an increase in IAA oxidase activity and decreasedAAU. The large increases obtained at later times, viz. 48 and72 h, appear to be related primarily to the release of manganesedue to the degradation of protein bodies which proceeds underthe action of GA and also to increased AAU. The IAA oxidaseand peroxidase activities are close to control during this period.In light, however, IAA oxidase and peroxidase activities showmarked increase during the first 4 h but no significant changesare observed in Mn(II) level or AAU. The peak of Mn(II) observedat 8 h corresponds with lower activities of IAA oxidase andperoxidase but an increase in AAU. The changes in Mn(II) closelycorrespond with the changes in AAU in light, peroxidase andIAA oxidase activities keeping close to the control. It appearsthat GA action is related to increased Mn(II) due to increasedAAU which may be coupled to the peroxidase-IAA oxidase system.The study confirms the postulate given by us in an earlier paper.