Modulation of sucrose content by fructose 2,6-bisphosphate during photosynthesis in rice leaves growing at different light intensities

Abstract

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose content by fructose 2,6-bisphosphate during photosynthesis in rice leaves growing at different light intensities.-J. exp. Bot. 38: 828-833.The relationship between the rate of CO2 fixation and sucrose concentration in the leaves of rice (Oryza sativa L.) grown at different light intensities was investigated. Maximum sucrose content coincided with maximum rates of CO2 fixation, achieved at a photon flux density of 1600 μmol m-2 s-1. The levels of sucrose and fructose 2,6-bisphosphate were also compared in the leaves under different light intensities. Fructose 2,6-Msphosphate accumulated during growth at low light. The activity of fructose-6-phosphate 2-kinase was high in the leaves grown at low light while that of fructose-2,6-bisphosphatase was low. The activities of phosphoglucose isomerase and phospho-glucomutase were slightly increased by growth at low light The activities of UDP glucose pyrophosphorylase were adversely affected in vitro with increased concentrations of fructose 2,6-bisphosphate while those of sucrose phosphate synthase were moderately affected. Phosphoglucose isomerase and phosphoglucomutase were activated by fructose 2,6-bisphosphate (8-0 mmol m-3) by 12-15%. The results suggested that low light intensities during growth result in an accumulation of fructose 2,6-bisphosphate which modulates the key enzymes of sucrose biosynthesis thus regulating carbon flow under conditions of limited photosynthesis. © 1987 Oxford University Press.