Current perspectives on the regulation of whole-plant carbohydrate partitioning

Whole-plant carbohydrate partitioning is the process whereby carbon assimilated through photosynthesis is distributed from the leaves to the rest of the plant by transport through the phloem. Allocation of carbohydrates underlies all aspects of plant growth and crop yield. Yet, in spite of the extremely critical role this process has on plant function and development, very little is known about the genetic and molecular mechanisms that control carbohydrate partitioning. Plants employ different strategies for importing photoassimilates into the phloem. Recent findings have uncovered plasticity both in the modes of phloem loading and carbohydrates translocated. Sugar transporters play essential roles in phloem loading in many plant species, but it is not known how they are regulated. Studies into the transcriptional and post-translational regulation of sugar transporters provide insights into the cellular mechanisms governing their expression and functions. Recent exciting potential breakthroughs include the observations that sucrose transporter multimerization, subcellular localization and activity are regulated by reduction/oxidation (redox) potentials, and the identification of a protein that physically interacts with multiple sugar transporters, modulating their activities. In addition, redox-regulation influences starch synthesis in both source and sink tissues. Tantalizing clues are emerging relating to redox-regulation of phloem function and of long-distance carbohydrate partitioning. (C) 2010 Elsevier Ireland Ltd. All rights reserved.