SUCROSE SYNTHASE AND NATURAL RIPENING IN SUGARCANE

Sugarcane (Saccharum spp. hybrids) cultivars vary in the timing and extent of natural ripening, an increase in the sucrose concentration of stalk juice that increases sucrose recovery in the sugar industry. The present study was conducted to determine (i) what changes in sugar accumulation occur in individual internodes during ripening, and (ii) if changes in sucrose synthase (SS) activity accompany natural ripening in sugarcane. Sugar concentrations and SS activities were determined in elongating and sucrose-storing internodes of two sugarcane cultivars sampled at monthly intervals during the 1989-1990 and 1990-1991 harvest seasons in South Texas. Ripening was indicated by a decrease in elongation rate, increase in total sugar concentration, and increase in sucrose percent of total sugar over successive sampling dates. These changes occurred earlier and to a greater extent in 'CP 70-321', an early ripening cultivar, than in 'LCP 81-10', which ripens later in the season. The specific activity of SS did not change significantly during this same period. In this study, changes in SS activity did not appear to be related to ripening.