Abstract
Endosperm cell and starch granule (amyloplast) development of six maize (Zea mays L.) genotypes, normal, amylose-extender (ae), sugary (su), waxy (wx), amylose-extender sugary (ae su), and amylose-extender waxy (ae wx), was compared. Endosperms of all genotypes were indistinguishable at 14 days after pollination. Cells were highly vacuolated and those in the central crown area of the kernel contained small starch granules in close association with the nucleus. Cellular and nuclear enlargement occurred during endosperm development in all genotypes, and major and minor gradients in physiological age of endosperm cells were observed in all kernels. Amyloplast development varied with genotype. Plastid development in normal and wx cells was characterized by an initial starch granule formation followed by granule enlargement to cell maturity. Endosperms homozygous for ae (ae, ae su, and ae wx) developed abnormal plastid-granules. Secondary granule formations preceded development of abnormality in ae and ae su, but not in ae wx endosperms. In contrast to ae and ae su starch granules, ae wx granules were highly birefringent indicating a high degree of crystallinity. In all three ae genotypes, abnormality increased as a function of kernel and physiological cell age. The su mutant had two distinct effects on amyloplast development. First, a mobilization of the initially formed starch, and second a synthesis and accumulation of phytoglycogen and the formation of large rounded plastids. In ae su plastid development, there was a mobilization of the starch initially formed (resulting in irregularly shaped, nonbirefringent granules) but only small amounts of phytoglycogen were produced.
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