Seasonal Changes in Starch Synthetase Activity in Relation to Starch Content in Kiwifruit

This paper describes the seasonal changes in starch content of kiwifruit in relation to starch synthetase activity and also examines the properties of this enzyme in the two cultivars, "Hayward" and "Koryoku". The highest activity of starch synthetase was observed in the middle of October for "Koryoku" and in late October for "Hayward". The highest starch contents in "Koryoku" and "Hayward" were observed in the middle and late October or early November, respectively. These increases in starch coincided with the highest activities of starch synthetase. Starch content in early-ripening 'Koryoku' peaked around half a month earlier than in late-ripening "Hayward". Since the soluble solids content in "Koryoku" could not be used as a harvest index because suitable firmness was not kept, the highest starch content was selected as the index in a previous paper. Starch synthetase activity followed the pattern of increasing starch content during the maturation and could explain maturity. Starch synthetase activity is a better index of maturity than β-amylase activity, because it supports decreasing starch content during the harvest period of "Koryoku".