Novel Cytological Findings on Gametophyte Development and Embryogenesis in Wheat (Triticum aestivum L.)

A step-by-step study of the anther and ovule developments, sporogenesis, from pre-meiotic stages to anthesis in anthers and seed development in the ovary, was done in Triticum aestivum L. The results showed that the wall development at tetrasporangiate anthers was consistent with the monocotyledonous type. The anther locule was surrounded by two inner temporal cell layers, including the tapetal cells and the middle layer, and two outer permanent layers, including the endothecium and epidermis. Tapetum cells were observed as uni- or bi-nucleated in the maturity stage. Asynchronous cytokinesis during the meiosis of microsporocytes caused the formation of tetragonal tetrads. The mature pollen grains were monoporated and three-celled type. Different origins of the tapetum cells, the polarity of the tapetum cells, and callose formation around the microsporangial cells were novel findings. The ovule was bitegmic, tenuinucellate, and orthotropous initially, and anatropous in the late developmental stages. Chalazal megaspore was functional causing the formation of monosporic embryo sac type. Due to the proliferation of the antipodal cells, a modified Polygonum type of embryo sac was observed. The first zygote division occurred before the endosperm mother cell division and gave rise to equal cells. The nuclear endosperm was formed by dividing the nucleus of the endosperm mother cell. However, it became cellular in later stages. The endosperm involved three types of cells: an aleurone layer around the embryo sac, the endosperm cells around the embryo with dense cytoplasm, and the more giant and vacuolated endosperm cells away from the embryo. Deposition of the residual callose in the micropylar opening wall of the megaspores tetrad stage, variation in endosperm cell type, and some details of the developmental process are among the novel findings.

Keywords:

Gametogenesis , Megasporogenesis , Microsporogenesis , meiosis. pollen grain