Effect of Gene Dosage at High Amylose Loci on the Properties of the Amylopectin Fractions of the Starches

Abstract

The effect of gene dosage at the amylose‐extender (ae) locus of maize and the rigosus‐a (r_a) locus of peas on the amylopectin fraction of endosperm and cotyledon starch were examined. Amylopectin fractions were isolated by gel filtration, butanol complexing and a combination of the two methods. In general, increasing doses of the recessive allele at either locus resulted in amylopectin fractions with iodine spectra with absorption maxima at higher wavelengths and greater absorptivity. Starches from endosperm of differing ae dosage but homozygous waxy were found to contain no amylose by gel filtration. By debranching with pullulanase, these starches were shown to have increasing average chain length with increasing ae dosage. Additional data suggested that increasing dosage at the ae locus (regardless of the genotype at the waxy locus) or the r_a locus resulted in amylopectin with increasing linearity. In addition, short chained amylose (approximately 100 glucose units) was observed in all ae genotypes in a homozygous Waxy background and all r_a genotypes.