MOLECULAR PHYSIOLOGY OF STARCH SYNTHESIS IN THE POTATO (SOLANUM-TUBEROSUM L)

In potato, starch is synthesized with two different tempos in the leaf and in the tuber. In both cases, the enzyme ADP glucose pyrophosphory lase achieves the production of the activated glucosydic precursors of starch and represents the major regulatory step of that biosynthetic pathway. Its allosteric control by intermediate metabolites of photosy nthesis explains a large part of the diurnal rythmicity of starch synt hesis in the leaf. in the developing tuber however, active starch synt hesis is essentially supported by a high expression level of the ADP g lucose pyrophosphorylase. Starch accumulation being apparently coordin ated with that of storage proteins in the developing tuber, the nature of the relevant regulatory mechanisms constitutes a fundamental aspec t of the physiology oi tuberization. A significant achievement in the identification of these mechanisms came from the cloning and structura l analysis of the ADP glucose pyrophosphorylase B-subunit promoter and its comparison with promoters of genes encoding storage proteins of t he patatin group.