A Role for Fructose 2,6-Bisphosphate in the Regulation of Sucrose Synthesis in Spinach

The subceliular distribution of fructose 2,6-bisphosphate in spinach (Spinacia oleracea) leaves was studied using nonaqueous fractionation, showing that all, or almost all, is located in the cytosol. The amount of fructose 2,6-bisphosphate present in leaves during the diurnal cycle was measured and compared to the accumulation of starch and sucrose, and the amounts of selected phosphorylated intermediates in the leaf. Upon illumination, the level offructose 2,6-bisphosphate decreases, but prolonged illumination leads to an increase in the level to above that found in the dark, which accompanies the onset of rapid accumulation of starch in the