Sugar metabolism during growth and development in sugarcane internodes

Development of sugarcane (Saccharum spp. hybrids) genotypes with higher suc rose concentrations is desirable. Activities of sucrose-metabolizing enzyme s during development of internodal storage tissue mag determine the rate of total sugar accumulation and final sucrose concentration. Internodes of se ven commercial cultivars were tagged prior to elongation and sampled at int ervals from July until December during two growing seasons. Internode elong ation was completed by about 380 degrees C d (base temperature 18 degrees C ). Dry matter accumulated until about 800 degrees C d. Water content decrea sed from about 920 to about 720 g kg(-1) fresh weight (FW). Soluble acid in vertase and sucrose synthase (sucrose cleavage direction) had peaks of acti vity during elongation, then declined to lower levels. Neutral invertase an d sucrose-phosphate synthase activities increased during development. Sugar accumulated, and the sucrose to total sugar ratio approached 1.0 as intern odes developed, although the combined sucrose cleavage activity of the inve rtases and sucrose synthase in most internodes was greater than the synthet ic activity of sucrose-phosphate synthase. Sugar accumulation rate was not consistently correlated with activity of My enzyme assayed. Sucrose content during internode development was correlated with sucrose-phosphate synthas e activity and the difference between sucrose phosphate synthase and acid i nvertase activities. Sucrose content of mature internodes was not correlate d with any enzyme activity. The data do not support the hypothesis that suc rose 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 su garcane internodes.