The Influence of Boron on Starch Phosphorylase and its Significance in Translocation of Sugars in Plants

Bean leaves infiltrated with 4% glucose after a dark period synthesized more starch than leaves infiltrated with 4% glucose and various levels of boron. Analysis for boron concentration in the leaves indicated that the level of the element was within physiological range for plants. In vitro studies in the glucose-1-phosphate in equilibrium starch reaction show that boron influences the rate of the reaction but not the final equilibrium. A plot of 1/rate of reaction vs 1/glucose-1-phosphate concentration indicates that, at low levels of substrate, the boron combines with the substrate and influences the rate of starch synthesis. Because boron influences the synthesis of starch, a hypothesis is presented which could explain why translocation of sugars in plants is increased when the element is present in sugar feeding and in C/sup 14/ carbohydrate synthesis experiments.