Changes in the Activities of Sugars and Sugar Metabolic Enzymes in Grape Berries during Development

Accumulation of sugars is an important metabolic process that occurs during grape berry development. Sugars are transported into the berry mainly in the form of sucrose and are broken down into glucose and fructose by the enzymes invertase and sucrose synthase. Changes in activities of invertase and sucrose synthase in the juice of three table grape genotypes (Flame Seedless, Perlette and Muscat Hamburg) was studied during four developmental stages. The characteristic rapid increase in the rate of sugar accumulation in the juice throughout the development was preceded by the activity of invertase. At the same time the rate of sugar accumulation also increased the activity of sucrose synthase. There is a possibility that sugar accumulation in grape juice occurs by pathway involving changes in the activity of enzyme for this process to operate. The results of the present study suggests that in the grape genotypes studied, invertase and sucrose synthase activities are positively correlated with high berry sugar content.