Seasonal internode development and sugar metabolism in sugarcane

The profile of sugar concentration along the stalk of sugarcane (Saccharum sp, hybrids) varies during the growing season and between cultivars. This study was conducted to determine how sucrose accumulation and metabolism in storage tissue changes with development, how sucrose metabolism changes as the growing season advances, and if differences in sugar cleavage could be detected between an early cultivar, CP70-324, and a late cultivar, TCP81-3058. Elongating internodes of both cultivars were tagged at intervals from July to October during 1993 and 1994 in field plots near Mercedes, TX, The tagged internodes were periodically sampled during their development, and sugars and enzymes of sucrose cleavage, sucrose synthase (SS), acid invertase, and neutral invertase, were assayed. Internodes which developed later in the growing season were shorter and accumulated less dry weight than those that developed earlier, Total sugar and sucrose concentrations in the late internodes approached those of early internodes as they matured, Water content of all internodes decreased from about 900 to about 720 g kg(-1) during development; late internodes reached this low water content in less heat units than did early internodes. Activities of SS and both invertases were greatest in the youngest internodes. SS activity decreased with internode age to a steady state of 1.5 to 2 mu mol mg(-1) protein h(-1), while acid invertase activity decreased to about 0.5 to 0.8 mu mol mg(-1) protein h(-1). Neutral invertase activity was highly variable both among internodes of the same age and between sampling dates. No significant differences in sugar concentrations or enzyme activities were observed between the cultivars.