Characterization and Starch Properties of a Waxy Mutant in Japonica Rice Kitaake

A rice waxy mutant M6 was generated from a japonica rice cultivar Kitaake through gamma irradiation. In this study, we characterized the mutant and analyzed its starch properties. The M6 with milky opaque kernels had lower seed length, width, and weight than wild type. The cavity in the center of starch granule might be responsible for waxy appearance of M6 mature kernels. Sequence analysis of granule-bound starch synthase I (GBSSI) gene showed that there was a 23 bp duplication inserted into the exon 2, generating one stop codon. No GBSSI protein was detected in the endosperm of M6. The isolated starch showed similar ratio of short and long branch-chains of amylopectin between M6 and wild type, but the M6 starch had no amylose. Both the M6 and wild type had A-type starch, but the M6 starch exhibited higher relative crystallinity than wild type starch. Compared with wild type starch, the M6 starch had significantly high swelling power, gelatinization enthalpy and breakdown viscosity and low water solubility, gelatinization peak temperature, peak viscosity, hot viscosity, final viscosity and setback viscosity. The M6 starch had significantly lower resistance to amylase hydrolysis than wild type starch.