Carbon partitioning in sugarcane internodal tissue with special reference to the insoluble fraction

[摘要] ENGLISH ABSTRACT:The changes in carbon allocation to sucrose, hexoses, fibre, starch and respirationwere investigated in developing internodes of sugarcane. Radiolabelling studies wereconducted on internode 3, 6 and 9 tissue, representing three stages of increasingmaturity. It was apparent that a high rate of cycling between triose-phosphate andhexose-phosphate occurred. A maximum of 50% of carbon entering triose-phosphateswas returned to hexose-phosphate in internode 3 tissue, and this flux decreased withtissue maturity to 30%. Carbon partitioning into sucrose increased from 34% of total14C uptake in internode 3, to 61% in internodes 6 and 9. In immature tissue, theprotein and fibre components were the dominant competing sinks with sucrose forincoming carbon, to which 14 and 16% of carbon were allocated respectively.Increased carbon allocation to sucrose with tissue maturity, coincided with a decreasein partitioning to fibre. This indicated that previous studies had underestimated totalcarbon allocation to respiration, since the protein component was not considered. Incontrast with earlier work, the respiratory pathway was the strongest competitor withsucrose for incoming carbon, even in mature tissue. Between internodes 3 and 6,carbon allocation to total respiration did not change significantly, but decreased 50%in mature tissue. Starch was a weak competitor with sucrose, for incoming carbon, towhich a maximum of 2% of 14Cwas allocated in immature tissue. In cane harvested inearly spring, radiolabelled maltose was recovered in internode 3 tissue of ripeningcane, indicating that concomitant starch synthesis and degradation occurred. The.redistribution of C-1 and C-6 in starch glucose was analysed following feeding oftissue with [1_14C]_and [6_14C]_glucose. Randomization of label in starch indicatedthat the pathway for carbon movement into sugarcane plastids for starch synthesis isprimarily through the triose-phosphate translocator. Finally, this study indicated thatradiolabelling of tissue discs is a suitable experimental system to determine carbonflux in sugarcane. During the 3 h labelling period the rate of 14C02 release becamelinear, indicating that the system approached isotopic steady state between the externaland internal glucose pool; and the respiratory processes involved in CO2 release.

[发布机构] Stellenbosch University