THE ISOLATION AND CHARACTERIZATION OF NOVEL LOW-AMYLOSE MUTANTS OF PISUM-SATIVUM L

Mutants of Pisum sativum L. with seeds containing low-amylose starch w ere isolated by screening a population derived from chemically mutagen ized material, In all of the mutant lines selected, the low-amylose ph enotype was caused by a recessive mutation at a single locus designate d 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 mu tants was reduced but not eliminated, These results provide further ev idence that amylose synthesis is unique to GBSSI, Other granule-bound isoforms of starch synthase cannot substitute for this protein in amyl ose synthesis, Examination of iodine-stained starch granules from muta nt embryos by light microscopy revealed large, blue-staining cores sur rounded by a pale-staining periphery, In. this respect, the low-amylos e 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.