Characterization of the dominant mutant amylose-extender (Ae1-5180) maize starch

Maize plants homozygous for the dominant amylose extender allele Ae1-5180 were self-pollinated and crossed onto wild type Ae plants, and vice versa, to obtain endosperms with zero to three doses of the Ae1-5180 allele. Starches from dominant Ae mutant kernels were isolated and analyzed with respect to molecular size distribution, amylose contents (iodine affinity), thermal properties (differential scanning calorimetry), and microscopic structure (scanning electron microscopy). Gel-permeation chromatograms of these starches showed greater proportions of amylose and intermediate fractions than those from normal maize starch. The iodine-staining blue value of the amylopectin peak on the profile results revealed longer amylopectin branch-chain lengths than those of normal corn, which was confirmed by enzyme debranching. The structure of the intermediate component and amylopectin was also revealed by gel-permeation chromatography and high-performance anion-exchange chromatography. Greater dosage of the Ae1-5180 gene did not increase amylose content (33%). The differential scanning calorimetry thermograms indicated that all the mutant starches with different dosages had similar thermal properties. The gelatinization onset temperature (T o ) range was 65.7-67.0°C and the gelatinization range (R) was 54.0-109.7°C. The scanning electron microscope showed that the mutant starches had irregular and round-shaped granules with diameters that ranged from 4 to 18 mm.