Invertase Activity and Abscisic Acid in Relation to Carbohydrate Status in Developing Soybean Reproductive Structures1

Abstract

The relationships among soluble acid invertase, carbohydrate concentrations, and abscisic acid (ABA) were examined in developing soybean [Glycine max L.(Merr.)] reproductive structures. Ontogenetic changes in enzyme activity and sucrose/glucose concentrations in flowers, pod walls, and immature seeds were followed from 2 to 30 days following flowering in growth chamber‐grown plants. The effect of exogenous ABA treatments on pod wall acid invertase and soluble carbohydrates was investigated in relation to the fluctuations in endogenous ABA in pod walls and seeds. The objective of the study was to determine potential mechanisms that may regulate early embryogenesis in soybeans. Flowers exhibited the highest acid invertase activity and activity in pod walls and seeds declined progressively from 2 to 30 days after flowering. Concentrations of sucrose and glucose in the respective tissues reflected invertase activity. Exogenous ABA stimulated invertase activity in 20‐to 25‐day old pod walls incubated in the presence of sucrose. Glucose concentrations recovered in the pod‐wall incubation medium also increased in the presence of ABA (1 to 100 μM), in accordance with the increase in invertase activity. The importance of glucose for development of immature seeds was demonstrated in experiments which showed that glucose was more effective than sucrose in enhancing the growth of seeds cultured in vitro. The data indicate that conversion of sucrose to glucose and possible regulation of acid invertase by ABA may play an important role in the growth of young soybean reproductive structures.