Amylopectin and Intermediate Materials in Starches from Mutant Genotypes of the Oh43 Inbred Line.

Amylopectin (AP) and intermediate materials (IM) from five endosperm mutant genotypes in a common Oh43 inbred line were isolated and examined by gel-permeation chromatography, iodine affinity, blue value (BV), and viscosity. The chain-length distributions of AP and IM were determined using an enzymatic- chromatographic method. The degrees of branching in AP and IM decreased when the amylose-extender (ae) gene was present. The dull-1 (du1) gene produced AP and IM with the highest degrees of branching among the samples. The ae starch had a significantly (P less than 0.01) longer peak average chain length (CL) of the long-B chains in the IM fraction (177 glucose units) than did the AP faction (73 glucose units) or the other starches (37-56 glucose units). The higher iodine affinity in ae starch of the IM (6.1) compared with that of the AP (2.8) supported the idea that the IM had a longer CL than did the AP. There were no significant differences in the peak CL of A or B chains in AP and IM fractions of brittle-1 (bt1), du1, ae bt1, and ae du1 starches. The IM of ae and ae du1 starches had higher BV than did the AP fractions; however, the IM of du1 and ae bt1 had lower BV than did the AP fractions. The limiting viscosity number and gel- permeation chromatography results indicated that the AP and IM fractions of bt1 and du1 starches possessed more branching and larger hydrodynamic volume properties than those of the ae, ae bt1, and ae du1 starches. The present study demonstrated that genetic background affects the CL of starch branches, degree of branching, and iodine binding properties of starches

Characterization of Starch Structures of 17 Maize Endosperm Mutant Genotypes with Oh43 Inbred Line Background.

The characteristics of starches from 17 endosperm mutant genotypes in a common Oh43 inbred background were examined by gel-permeation chromatography (GPC), iodine affinity (IA), and scanning electron microscopy (SEM). The chain-length distributions of amylopectins were determined by an enzymatic- chromatographic method. Each genotype exhibited distinctive GPC elution patterns of its native and isoamylase-debranched starches and distinctivemorphology as noted by SEM. The amylose-extender (ae), dull-1 (du1), and sugary-1 (su1) genes were associated with increased amounts of amylose and intermediate fractions compared with normal starch. The waxy (wx) gene was epistatic to other genes relative to the accumulation of amylopectin, which was consistent with work done elsewhere. The discrepancy in amylose percentage determined by GPC and IA in some genotypes may have resulted from the presence of a large amount of intermediate materials in those genotypes, which could not always be distinguished from amylose by the IA method. For example, in ae starch, most of the intermediate materials were measured as amylose by the IA procedure, whereas in du1, ae brittle-1 (bt1), and ae du1 starches, most of the intermediate materials were exclded from IA measurements. The intermediate fractions from each genotype in the GPC elution profiles also differed from each other, suggesting differences in molecular weight and/or branching. The proportions of long B chains and the average chain length of amylopectins were increased when the ae gene was present. In contrast, the du1 gene decreased the proportions of the long B chains of amylopectins. The mutants containing he ae gene showed low degrees of branching in amylopectin; mutants containing the du1 and/or su1 genes hd high degrees of branching. Genetic background played a major role in determining the fine structure of starch components. The effects of interactions between recessive mutant genes on the structures and morphology of different starch genotypes were evident