MOLECULAR APPROACHES TO THE MANIPULATION OF CARBON ALLOCATION IN PLANTS

In plants, sucrose is the end product of photosynthesis and is convert ed to a wide variety of storage compounds in tissues such as seeds and tubers. The allocation of carbon from sucrose to the various metaboli c pathways leading to these products will determine the quantity of ea ch synthesized in the respective storage organs. If the level of the e nzymes involved in the allocation of carbon could be changed by geneti c manipulation, it is probable that the relative yields of the various storage products can also be altered. The initial breakdown of sucros e occurs in the cytosol of the cell. Many biosynthetic pathways, howev er, including those involved in the synthesis of storage products such as fatty acids, starch, and amino acids, occur in the plastid. The di stribution of carbon substrates for these processes will be determined , to a large extent, by the flux of carbon through the glycolytic path ways found in both the cytosolic and plastid compartments. This articl e will discuss the importance and consequences of compartmentation, re view the extent of our understanding of glycolysis and other enzymes a nd pathways regulating carbon allocation, and will speculate on the po tential for the genetic manipulation of these pathways.