The isolation and characterization of novel low‐amylose mutants of Pisum sativum L.

Abstract

ABSTRACTMutants of Pisum sativum L. with seeds containing low‐amylose starch were isolated by screening a population derived from chemically mutagenized material. In all of the mutant lines selected, the low‐amylose phenotype was caused by a recessive mutation at a single locus designated lam. In embryos of all but one mutant line, the 59 kDa granule‐bound starch synthase (GBSSI) was absent or greatly reduced in amount. The granule‐bound starch synthase activity in developing embryos of the mutants was reduced but not eliminated. These results provide further evidence that amylose synthesis is unique to GBSSI. Other granule‐bound isoforms of starch synthase cannot substitute for this protein in amylose synthesis. Examination of iodine‐stained starch granules from mutant embryos by light microscopy revealed large, blue‐staining cores surrounded by a pale‐staining periphery. In this respect, the low‐amylose mutants of pea differ from those of other species. The differential staining may indicate that the structure of amylopectin varies between the core and peripheral regions.