Sugar Metabolism during Growth and Development in Sugarcane Internodes

Abstract

Development of sugarcane (Saccharum spp. hybrids) genotypes with higher sucrose concentrations is desirable. Activities of sucrosemetabolizing enzymes during development of internodal storage tissue may determine the rate of total sugar accumulation and final sucrose concentration. Internodes of seven commercial cultivars were tagged prior to elongation and sampled at intervals from July until December during two growing seasons. Internode elongation was completed by about 380°C d (base temperature 18°C). Dry matter accumulated until about 800°C d. Water content decreased from about 920 to about 720 g kg−1 fresh weight (FW). Soluble acid invertase and sucrose synthase (sucrose cleavage direction) had peaks of activity during elongation, then declined to lower levels. Neutral invertase and sucrose‐phosphate synthase activities increased during development. Sugar accumulated, and the sucrose to total sugar ratio approached 1.0 as internodes developed, although the combined sucrose cleavage activity of the invertases and sucrose synthase in most internodes was greater than the synthetic activity of sucrose‐phosphate synthase. Sugar accumulation rate was not consistently correlated with activity of any enzyme assayed. Sucrose content during internode development was correlated with sucrose‐phosphate synthase activity and the difference between sucrose‐phosphate synthase and acid invertase activities. Sucrose content of mature internodes was not correlated with any enzyme activity. The data do not support the hypothesis that sucrose synthase activity is related to the rate of sugar accumulation, but do support the hypothesis that sucrose‐phosphate synthase and acid invertase play key roles in determining sucrose concentration during maturation in sugarcane internodes.