Expression of granule‐bound starch synthase in developing rice grain

The expression of granule‐bound starch synthase (GBSS) in rice (Oryza sativa) genotype Tainung 67 (200 g kg^?1 grain amylose content) and its two NaN₃‐induced mutants SA419 and SA418 were examined. G/T polymorphism analysis indicated that SA418 (300 g kg^?1 grain amylose content) carried Wx^a allele. The insertion of 23 base pairs sequence was found only in SA419 (80 g kg^?1 grain amylose content), suggesting that it was a waxy mutant. Microsatellite polymorphisms (CT)_n were also detected on the Wx gene encoding GBSS in the tested genotypes. The activities of several key enzymes involving starch biosynthesis in developing grains of field‐grown rice plants were also compared during grain filling period. Significant genotypic differences were only found in the expression of GBSS. The content of amylose in SA418 grain was higher than Tainung 67 and SA419 grains throughout the entire grain filling period, possibly due to its superiority to synthesize amylose through GBSS. The lowest amylose content of SA 419 grain was attributable to its extremely low activity of GBSS in comparison with the two other genotypes. The mutation effects on the expression of GBSS were confirmed by two‐dimensional electrophoresis and mass spectrometry. Copyright © 2007 Society of Chemical Industry