Endosperm morphogenesis in wheat (Triticum aestivum L.) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dv13zx74v

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  • Wheat endosperm morphogenesis was studied by light microscopy during the entire growth period of anthesis to maturity. Four developmental stages have been described in this thesis: (1) double fertilization, (2) formation of the lower endosperm cells, (3) termination of nuclear divisions, and (4) initiation of protein bodies. The first manuscript reviews double fertilization and provides photographs of the embryo sac, pollen tube growth, syngamy and triple fusion. The descriptions made by previous researchers are compared with the observations of the writer. Early endosperm growth was characterized by nuclear divisions without formation of cell walls. During the first 4 days of growth, dense endosperm cells were formed above the embryo by a unique and previously undescribed mechanism. Cytoplasmic vesicles were formed in the upper endosperm, bordering the antipodals. Those vesicles fell to the gravitational bottom of the embryo sac, coalesced and were divided into cells by walls growing in from the nucellus. Later, those cells were entirely consumed by the developing embryo. Morphogenetically, cytoplasmic vesicles were the mechanism by which nutrients were transferred from the antipodals to the lower endosperm and ultimately to the embryo. The upper embryo sac vacuole was cellularized by cytoplasmic projections from the endosperm nuclei. The nuclei then divided in all areas of the embryo sac, as long as space was available. During the ninth to twelfth days after anthesis, the cuticularized inner integument and nucellar epidermis stopped growing. That limited the space available for nuclear divisions in the endosperm. Between the thirteenth and fifteenth days after anthesis, endosperm nuclei stopped dividing. It is concluded that endosperm nuclear division was limited to the space within the inner integument and nucellar epidermis. Because that space stopped increasing by 14 days after anthesis, endosperm cell number was spacially limited. After cell formation had ceased, the endosperm nuclei released their nucleoli into the cell vacuole. Those nucleoli enlarged and acquired safranin stain like protein bodies. The nuclei broke down and released other chromosome-sized particles which also united and formed protein bodies. It is concluded that wheat endosperm protein bodies originate from nucleoli.
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