Structural changes during development in the amylose and amylopectin fractions (separated by precipitation with concanavalin A) of starches from maize genotypes

Abstract

The starches from four maize genotypes (waxy, normal, amylose-extender, and ae ae/wx wx) have been sampled at three stages of development, and fractionated by precipitation of the amylopectin with concanavalin A. The resulting amylose and amylopectin fractions were examined by gel chromatography before and after treatment with debranching enzyme. Both mature and immature samples were efficiently fractionated. The proportion of amylose in the starches of the n and ae genotypes, measured by concanavalin A precipitation, increased on development. A small proportion of the ae/wx mutant starch was not precipitated by concanavalin A, and its properties were those of an “intermediate fraction” of low molecular weight with a degree of branching and average chain-length intermediate between amylose and amylopectin. The amylose of n starch increased in molecular size during development, whereas that of ae decreased. No differences in molecular size and chain-length distribution were detected within a genotype for the amylopectins of wx, n, and ae/wx starches during development, but the component from ae starch decreased in molecular size and increased in average chain-length. Comparison of the amylopectins from wx, n, and ae starches showed a decrease in molecular size and an increase in average chain-length, in that order.