Initital cellularization and differentiation of the aleurone cells in the ventral region of the developing wheat grain.

Early cellularization of the free-nuclear endosperm and subsequent differentation of the aleurone cells in the ventral region of the developing wheatgrain (Triticumaestivum L. cv. Heron) were examined using both light and electron microscopy. In ovules harvested 1 d after anthesis, irregular wall ingroths typical of transfer cells protrude into the multinucleate cytoplasm. Initital cellularization occurs by a process of free wall formation in much the same fashion as in the dorsal region of the grain. In places, sheets of endoplasmic reticulum and dictyosomes appear to be closely associated with the growing wall. Like the wall ingrowths noted earlier, the freely growing walls are intensely fluorescent after staining with aniline blue. Initiatal cellularization is complete 2-3 days after anthesis. Unlike the first-formed cells in the dorsal region of the developing grain, those in the ventral region are not meristematic. These amitotic cells become the groove aleurone cells which at an early stage of development are set apart from the rest of the endosperm by their irregularly thickened walls and dense cytoplasm. Autofluorescence is first apparent in the walls of those cells next to the degenerating nucellus. In contrast to the aleurone cells in the dorsal region of the grain, at maturity only the inner wall layer of each of the groove aleurone cells remains autofluorescent. The aleurone grains are highly variable in appearance and contain no Type II inclusions.