Early Stages in the Development of Wheat Endosperm. I. The Change From Free Nuclear to Cellular Endosperm

Abstract

The cytological features of the cellularization of the free nuclear endosperm of wheat are described. Following the initial proliferation of nuclei the endosperm is divided into a small ventral area and a larger dorsal area which then develop separately. Cell wall formation in both regions is independent of a mitotic spindle and appears to be mediated by freely growing walls. Wall material is laid down along lines already marked out by ingrowth from the plasma membrane into the central cell cyto- plasm. By the time that cellularization is complete the smaller ventral region has been transformed into a layer of small, thick-walled cells whilst the larger dorsal area contains large, highly vacuolate endosperm cells. A model is proposed which endeavours to link the morphological features observed in embryo sacs, collected from wheat ovules 2-6 days after anthesis, into an ontogenetic sequence. This model is compared with previously published descriptions of wheat endosperm development.