The regulation of carbon metabolism in non-photosynthetic tissues (sinks) of higher plants is poorly understood, despite the fact that these tissues constitute the bulk of the world's supply of food. Photosynthetically derived carbon is generally translocated to sinks as sucrose but, once unloaded, may be processed in different ways. Depending on the type of sink, the imported sucrose may be used predominately in biosynthesis and respiration, or stored, either as sucrose or starch. Little is known about the biochemical mechanisms by which this partitioning is accomplished. These studies will make significant contributions to the understanding of carbon metabolism in sink tissues, an area of plant biology in urgent need of development. Fructose 2,6-bisphosphate (F2,6P2), a regulatory molecule shown to control carbon partitioning in photosynthetic cells, may play a related role in sinks as well. The concentration of F2,6P2 is determined by the activities of fructose 6-phosphate, 2-kinase (F6P, 2K) and fructose 2,6-bisphosphatase (F2,6P2ase), which synthesize and degrade F2,6P2. The Fellow will purify F6P,2K and F2,6P2ase from a variety of sink types to determine whether differences in the properties of the enzymes correlate with different patterns of carbon partitioning. With the purified preparations, the affinity of the enzymes for their substrates and their sensitivity to metabolite effectors will be measured. It will be determined whether sink F6P,2K and F2,6P2ase reside on separate proteins as in leaves, and tested whether the enzymes might be regulated by covalent modification (for example, phosphorylation).
