Isolation and characterisation of novel starch mutants of oats

Mutagenised grains of the diploid oat, Avena strigosa Schreb., were screened for altered starch granules in the endosperm. Three mutant lines were identified: mutants lam-1 and lam-2 had granules that stained red with iodine solution and sga-1 had endosperm containing soluble material that stained red with iodine solution, as well as blue-staining starch granules. The lam-1 and lam-2 lines lack or have severely reduced amounts of granule-bound starch synthase activity, the granule-bound starch synthase I protein and the amylose component of starch in the endosperm. They therefore represent mutations of the waxy type. The red-staining, soluble material in the sga-1 mutant is very similar in appearance and chain-length profile to the phytoglycogen that accumulates in the endosperms of the sugary-1 mutants of cereals. All sugary-1 mutants lack or have reduced amounts of isoamylase activity. However, native gel assays reveal a normal isoamylase activity in the developing endosperms of sga-1 suggesting that it is not of the sugary-1 type. The nature of the mutation responsible for the sga-1 phenotype has yet to be discovered.