BIOREGULATION OF STARCH ACCUMULATION IN DEVELOPING SEEDS

Starch is a major constituent of cereal and most legume seeds and, thus, an important determinant of yield of these seeds, This paper reviews the processes controlling starch deposition in the developing seeds, The capacity of the seed (i.e. cell and amyloplast numbers) to accommodate starch is determined during the first one-third phase of seed development and the availability of carbohydrates to the seed during this phase influences this capacity, Sucrose is the primary source of reduced carbon for starch synthesis in the seeds, In the cytosol of starch-storing cells, sucrose is catabolized to generate hexose phosphates (Glc-1-P or Glc-6-P), which are transported into the amyloplast, These are used to generate ADPGlc by ADPGlc-PPase, which is then used by starch synthase(s) and branching enzymes to produce starch, Although the regulatory role of ADPGlc-PPase (i.e. its activation by 3-PGA and inhibition by Pi) in starch metabolism in photosynthetic tissues is well documented, based on kinetic characteristics and molecular biology studies, its similar role in the developing seeds has been questioned.