Changes in the activities of enzymes concerned with sugar metabolism during the development of grape berries

Abstract

Changes in activities of invertase, hexokinase, glucose 6-phosphate dehydrogenase, sucrose synthetase, sucrose phosphate synthetase and sucrose phosphatase in extracts prepared with Carbowax 4000 were studied at weekly intervals during the development of sultana grape berries. The characteristic rapid rise in the rate of sugar accumulation by the berries about halfway through development was preceded by an increase in the activity of invertase. At about the same time that the rate of sugar accumulation increased the activities of sucrose synthetase, sucrose phosphate synthetase and sucrose phosphatase increased. The activity of glucose 6-phosphate dehydrogenase decreased early in the development of the berries and remained low. The possibility that sugar accumulation in grapes occurs by a pathway involving the synthesis and hydrolysis of sucrose phosphate is discussed in terms of the changing activities of the enzymes necessary for this pathway to operate.