UNDERSTANDING THE GENETICS OF AMYLOPECTIN STRUCTURE AND FUNCTION THAT AFFECTS THE COOKING PROPERTIES OF RICE

摘要

The amount and structure of amylose and amylopectin components of the grain starch govern the cooking properties of rice. Amylose, a linear a-1, 4-polyglucans, is synthesised by the granule bound starch synthase and is responsible for the texture of cooked rice. Amylopectin (a-1, 6-branched polyglucans) on the other hand is synthesised by the soluble starch synthase (SSS) and a number of branching and de-branching enzymes that function in a coordinated manner to generate a highly branched structure unique to a specific rice line. One of the SSS that plays a key role in amylopectin synthesis is SSIIa, which incorporates mainly the long chains thus affecting the structure and gelatinisation temperature (GT) of the starch (Nakamura et al, 2005; Waterset al 2006, Bao et al, 2006). In the SSIIa gene, a number of single nucleotide polymorphs (SNP) have been identified in rice and some of them result in amino acid changes in the active site of the SSIIa enzyme, thus altering its activity and the overallamylopectin structure (Nakamura et al, 2005). In order to understand the genetic basis of amylopectin structure and its effects on the cooking gelatinisation temperature, the main objectives of this study were to analyse diverse rice lines for their GT and amylopectin chain length distributions, and to correlate that with the combinations of the SSIIa alleles present.