Polarization colors of lightly iodine-stained maize starches for amylose-extender and related genotypes in the W64A inbred line

Previous qualitative research showed that for some maize endosperm genotype starches the color of variably iodine-stained starch granules observed by bright field microscopy (BFM) was different from the color of identically stained granules observed by polarized light microscopy (PLM). One objective of the present study was to determine the polarization color for a variety of high-amylose and other starch genotypes in an identical genetic background. A secondary objective was to determine the iodine concentration dependence of polarization colors for the samples. Starches from the W64A inbred line were obtained from the following genotypes: normal, wx, ae, du, su2, ae wx, ae du, ae su2, and du su2. Starches were stained with iodine solutions ranging from 0.02 to 0.075% and viewed with BFM and PLM, using an auto-exposure digital camera function. Most starches showed the first appreciable color at about 0.04% I-2. Unlike normal and non-ae-containing starches, ae starch showed a pink polarization color, despite its blue color in bright field. Heterogeneity in polarization color was observed both within and among granules. Double mutant starches containing ae showed variable effects, depending on the combination. It is suggested that the pink polarization color of ae starch may be due to a lack of symmetrical orientation of iodine-complexed amylose in these granules.