ABSTRACT
This chapter discusses the partial reactions of photoassimilate partitioning that involve transport across cellular membranes. The main impetus for the advancement of the field of sugar transport has come from the implementation of the methods of molecular biology in the study of assimilates transport. The autotrophic regions of the plant may be widely separated from heterotrophic regions, or they may be adjacent to one another, as with the epidermis and the underlying mesophyll cells in the leaf. Heterologous expression and complementation of mutations in heterologous hosts are approaches that will likely be used in the near future to identify and isolate genes encoding a variety of transporters. A superficial inspection of transport mechanisms reveals that the antiport-symport paradigm is found repeatedly in prokaryotic and eukaryotic cells. Triose sugar transport across the inner chloroplast membrane is catalyzed by a carrier that links the metabolic requirements of the cell to the synthetic machinery of the chloroplast.
