Characterization of starch structures and properties of maize mutants from the Oh43 inbred line
Starches were isolated from a dent maize (Zea mays L.) inbred line Oh43, from single endosperm mutants and from the double-mutant combinations within Oh43. The thermal properties of the starches, including onset temperature (T[subscript] o), peak temperature, gelatinization temperature range, and enthalpy ([delta]H) of gelatinization and retrogradation and percentage of retrogradation, were determined by differential scanning calorimetry. A Voland-Stevens texture analyzer was used to measure gel strength. Double mutants generally had higher T[subscript] o and [delta]H for gelatinization and lower T[subscript] o for retrogradation, and lower gel strength measurements than those of single mutants. Sixteen mutant genotypes along with the normal genotype were selected for characterization of their fine structures and physicochemical properties. Each genotype exhibited different elution patterns of its native and isoamylase-debranched starches by gel permeation chromatography (GPC), and showed distinctive morphology revealed by scanning electron microscopy. The amylose-extender (ae), dull-1 (du1), and sugary-1 (su1) genes were associated with increased amounts of amylose and intermediate materials, whereas the waxy (wx) gene produced starch with essentially 100% amylopectin. The discrepancy in amylose percentage by using GPC and iodine affinity in some genotypes may have resulted from the presence of a large amount of intermediate materials in those starches. The mutants containing the ae gene had low amounts of branching in the amylopectin; mutants containing the du1 and/or su1 genes had a high amount of branching. Among all the structural characteristics, amylose content was the most important factor affecting the physicochemical properties. Other structural characteristics were weakly correlated with physicochemical properties. Five mutant genotypes (ae, brittle-1 (bt1), du1, ae bt1, and ae du1) were further fractionated, and the amylopectin and intermediate materials were obtained for study of their structural characteristics and physicochemical properties. The amylopectin and intermediate materials from the same starch source exhibited different structural characteristics and properties, as did their fractions from different starches. This study demonstrated that genetic background plays an important role in determining the fine structure of starch components. The effects were evident of interactions between recessive mutant genes on the structures and properties of starch.