Starch granule size distribution and morphogenesis in maize ('Zea mays' L.) grains with different endosperm types

In this study we investigated starch granule size distribution and morphogenesis in the grains of maize with different endosperm types. Four maize varieties including super-sweet (Huawei NO. 6), pop (Tebao NO. 2), waxy (Xixinghuangnuo NO. 6), and dent corns (Zhengdan 958) were examined for starch granule size distribution and arrangement within the grains using a laser diffraction grain size analyzer, transmission electron, and scanning electron microscopies. The distribution of starch granule volume formed a triple humped curve in which granules with a diameter of less than 2 mum were abundant, while greater than 15 mum were most prevalent. Super-sweet corn bucked the trend slightly, with granules from 2-15 mum predominating. Average diameter showed the following order: waxy>pop>dent>super-sweet. Correlation analysis indicated that grain weight and starch content were significantly correlated (0.649*, 0.764* ) with volume percentage in granules from 2-15 mum predominating, whereas other grain quality were not correlated with granule volume for size ranges. Transmission electron microscopy revealed a marked difference in the development of starch granules, protein and lipid bodies. In first layer endosperm cells, there were many protein and lipid bodies in waxy, super-sweet and dent corns, but none in the equivalent region of popcorn, which appeared to have a higher number of plastid starch granules. Vacuoles and most protein bodies were large in super-sweet corn. In second layer endosperm cells, pop, waxy, and dent corns contained many starch granules. In third layer endosperm cells, almost all starch granules were patterned in popcorn. In deep layer endosperm cells, patterned starch granules were plentiful in dent and super-sweet corn, but scarce in waxy and pop varieties. Lipid bodies and cell inclusions were more abundant in pop, dent, and waxy types than in super-sweet corn.