BIOREGULATION OF STARCH ACCUMULATION IN DEVELOPING SEEDS

Starch is a major constituent of cereal and most legume seeds and, thu s, an important determinant of yield of these seeds, This paper review s the processes controlling starch deposition in the developing seeds, The capacity of the seed (i.e. cell and amyloplast numbers) to accomm odate starch is determined during the first one-third phase of seed de velopment and the availability of carbohydrates to the seed during thi s phase influences this capacity, Sucrose is the primary source of red uced carbon for starch synthesis in the seeds, In the cytosol of starc h-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 st arch synthase(s) and branching enzymes to produce starch, Although the regulatory role of ADPGlc-PPase (i.e. its activation by 3-PGA and inh ibition by Pi) in starch metabolism in photosynthetic tissues is well documented, based on kinetic characteristics and molecular biology stu dies, its similar role in the developing seeds has been questioned.