CARBON PARTITIONING IN THE SUGARCANE STALK

The study was aimed at determining the metabolic fate of sucrose in intact sugarcane NCo376 internodal tissue. For this purpose, a single leaf was pulsed with 14CO2 for 10 min.Within the first 6 hours after labelling, more than 80% of the fixed carbon was translocated out of the leaf and the majority of the export product was sucrose. Distribution of the radiolabelled sucrose to, and the sugar content of, immature, intermediary and mature internodal tissue were analysed. The highest sucrose content was in the mature internode but the highest rate of sucrose accumulation occurred in the intermediary internodal tissue. Sucrose was exported both upwards and downwards in the stem after export from the leaf. The internodes below the feeding site accumulated most of the radio-label. In the immature internodes, a significant portion of label was lost during the first 7 days, whereafter most of the label was trapped in the water insoluble components. Internodal maturation was associated with a redirection of carbon from non-sucrose cellular organic fractions to sucrose storage. Concomitant with the increased carbon partitioning into stored sucrose down the developing stem is a decrease in carbon partitioning into the hexose sugar pool. The distribution of radio-label shows that that sucrose turnover is occurring in both immature and mature internodal tissue.