THE CONTROL OF SOURCE TO SINK CARBON FLUX DURING TUBER DEVELOPMENT INPOTATO

We have used top-down metabolic control analysis to investigate the co ntrol of carbon flux through potato (Solanum toberosum) plants during tuberisation. The metabolism of the potato plant was divided into two blocks of reactions (the source and sink blocks) that communicate thro ugh the leaf apoplastic sucrose pool. Flux was measured as the transfe r of C-14 from CO2 to the tuber. Flux and apoplastic sucrose concentra tion were varied either by changing the light intensity or using trans genic manipulations that specifically affect the source or sink blocks , and elasticity coefficients were measured. We have provided evidence in support of our assumption that apoplastic sucrose is the only comm unicating metabolite between the source and sink blocks. The elasticit y coefficients were used to calculate the flux control coefficients of the source and sink blocks, which were 0.8 and 0.2, respectively. Thi s work suggests that the best strategy for the manipulation of tuber y ield in potato will involve increases in photosynthetic capacity, rath er than sink metabolism.