Carbon allocation to the insoluble fraction, respiration and triose-phosphate cycling in the sugarcane culm

The changes in carbon allocation to non-sucrose metabolic pathways were investigated in developing internodes of sugarcane. Radiolabelling studies were done on internode 3, 6 and 9 tissues, representing three stages of increasing maturity. Carbon partitioning into sucrose increased from 34% of total 14 C uptake in internode 3, to 66% in internodes 9. In immature tissue, the protein and fibre components were the dominant competing sinks with sucrose for incoming carbon, to which 14 and 16% of carbon was allocated. Increased carbon allocation to sucrose with tissue maturity coincided with a decrease in partitioning to fibre and total respiration. Between internodes 3 and 9 carbon allocation to total respiration decreased by 9%, and to fibre by 14%. Carbon cycling between the triose- and hexose phosphate pools was evident in all internodes. More than 90% of carbon entering triose-phosphates was returned to hexose in internode 3 tissue, and this flux decreased with tissue maturity.