I. Tan

Effects of starch synthase IIa gene dosage on grain, protein and starch in endosperm of wheat

Starch synthases (SS) are responsible for elongating the α-1,4 glucan chains of starch. A doubled haploid population was generated by crossing a line of wheat, which lacks functional ssIIa genes on each genome (abd), and an Australian wheat cultivar, Sunco, with wild type ssIIa alleles on each genome (ABD). Evidence has been presented previously indicating that the SGP-1 (starch granule protein-1) proteins present in the starch granule in wheat are products of the ssIIa genes. Analysis of 100 progeny lines demonstrated co-segregation of the ssIIa alleles from the three genomes with the SGP-1 proteins, providing further evidence that the SGP-1 proteins are the products of the ssIIa genes. From the progeny lines, 40 doubled haploid lines representing the eight possible genotypes for SSIIa (ABD, aBD, AbD, ABd, abD, aBd, Abd, abd) were characterized for their grain weight, protein content, total starch content and starch properties. For some properties (chain length distribution, pasting properties, swelling power, and gelatinization properties), a progressive change was observed across the four classes of genotypes (wild type, single nulls, double nulls and triple nulls). However, for other grain properties (seed weight and protein content) and starch properties (total starch content, granule morphology and crystallinity, granule size distribution, amylose content, amylose–lipid dissociation properties), a statistically significant change only occurred for the triple nulls, indicating that all three genes had to be missing or inactive for a change to occur. These results illustrate the importance of SSIIa in controlling grain and starch properties and the importance of amylopectin fine structure in controlling starch granule properties in wheat.

“Structure-Property” Relationships of Genetically Modified Starch

Starch is an attractive raw material for biodegradable plastic applications. However, the use of starch in biodegradable plastic applications is yet limited by its structural and functional properties, which are dictated by its genetic makeup. This chapter discusses the characterizations of a range of biotechnologically derived novel starches from different cereal sources to elucidate the relationship between starch structure and functionality. In summary, the following starch structure-functionality relationships are deduced. The variation in starch macromolecular properties can be attributed to their corresponding mutation of starch biosynthetic gene expression. Differences in starch amylose content affect the extent of structural order inside the granules, while the double-helix packing arrangement is influenced by the amylopectin chain length distribution. Starch gelatinization (MTDSC) thermal properties are mainly influenced by the amylopectin chain length distribution, while the swelling power and rheological properties are mainly affected by the amylose content.