Starch Granule Size Distribution in Maize Kernel with Different Endosperm Types

Maize(Zea mays L.)kernel dry weight contains about 70%starch.Many studies have focused on the effects of sowing date,variety and nitrogen top-dressing on starch granule distribution in single variety or two varieties.But starch granule size distribution in grains of different endosperm types of maize has not been clear yet.Four maize varieties including super-sweet corn(Huawei 6),popcorn(Tebao 2),waxy corn(Xixinghuangnuo 6)and dent corn(Zhengdan 958)were used to study the starch granule size distribution and the starch granule arrangement in grains by laser diffraction grain size analyzer,transmission electron and scanning electron microscopy.The results showed that distribution of starch granules volume in grains of the maizes were changed in a triple humped curve.The volume proportion of starch granules with diameter lower than 2μm was the least,while that with diameter higher than 15μm was the more(that with diameter from 2 to 15μm in super-sweet corn grain was the most). The average diameter showed following order:the waxythe popthe dentthe super sweet.Correlation analysis indicated that the grain weight and starch content were significantly correlated with the volume percentage of starch granules with diameter higher than 2μm;while the contents of protein,amino acid,crude fat and test weight had no correlation with volume of starch granule with all size ranges.Transmission electron microscopy showed that the starch granules in grains of dent and super sweet corn were rotund mostly,with a great deal of drapes.Starch granule arrangement of dent corn was sparse,with abundant lipid droplet, while that of super sweet corn was very sparse;with rich lipid droplet.The starch granule in grains of pop corn was square and oblong,and extruded one another,with thick and skimp drapes,with was highly compact with abundant lipid droplet.The starch granule in grains of way corn was rotund and elliptic,with low and skimp drapes,compact arrangement and abundant lipid droplets.Scanning electron microscopy showed that the starch granules in grains of dent,super sweet and waxy corn were spherical.A small quantity of depressed starch granules were demonstrated in dent corn,while none of depressed starch granules were detected in super sweet corn with reticulate configuration in surface of starch granules.Moreover the cell did not be filled with starch granules and filling agent.The starch granule was polyhedral in pop corn with a very few depressed starch granules.