MOLECULAR APPROACHES TO THE MANIPULATION OF CARBON ALLOCATION IN PLANTS

In plants, sucrose is the end product of photosynthesis and is converted to a wide variety of storage compounds in tissues such as seeds and tubers. The allocation of carbon from sucrose to the various metabolic pathways leading to these products will determine the quantity of each synthesized in the respective storage organs. If the level of the enzymes involved in the allocation of carbon could be changed by genetic manipulation, it is probable that the relative yields of the various storage products can also be altered. The initial breakdown of sucrose occurs in the cytosol of the cell. Many biosynthetic pathways, however, including those involved in the synthesis of storage products such as fatty acids, starch, and amino acids, occur in the plastid. The distribution of carbon substrates for these processes will be determined, to a large extent, by the flux of carbon through the glycolytic pathways found in both the cytosolic and plastid compartments. This article will discuss the importance and consequences of compartmentation, review the extent of our understanding of glycolysis and other enzymes and pathways regulating carbon allocation, and will speculate on the potential for the genetic manipulation of these pathways.