A MUTATION AT THE RB GENE, LOWERING ADPGPPASE ACTIVITY, AFFECTS STORAGE PRODUCT METABOLISM OF PEA SEED COATS

Seed coat development was studied on two near-isogenic lines of peas (Pisum sativum L.): RbRb (wild type, round seed) and rbrb (wrinkled seed), A mutation at the rb locus modifies the dry seed shape and reduces the starch content of the embryo, This mutation is now known to affect the activity of ADPGlucose pyrophosphorylase, a key enzyme in the starch biosynthetic pathway. We have investigated the effects of the rb mutation on seed coat development and found that the mutation reduces the growth rate and starch content in this organ, However, experiments on the kinetics of C-14-sucrose loading showed that starch synthesis from unloaded sucrose occurred in the seed coat for both mutant and wild-type lines. In addition, the sucrose concentration was increased and amino acid concentration decreased such that the nutritional balance of the embryos was affected. However, osmolality of the seed coat cells was not affected, suggesting a regulatory process which allows the maintenance of the import of assimilates in the seeds of either line.