| Sexual reproduction leads to the production of seeds and fruits. The first step of sexual reproduction is the interaction between the pollen and the stigma of the flower. The tapetum cells in the floral anther controls the maturation of the pollen and the constituents of the pollen coat. The characteristics of the tapetum and pollen coat can dictate the success or failure of pollination and thus sexual reproduction. This thesis is a study of the organelles in the tapetum cells and their contents, and of their selective retention on the pollen surface.;In Brassica napus, an insect/self-pollinating species, the tapetum cells in the anthers at the late stage of pollen maturation contained two predominant organelles. The two organelles, the plastids and lipid particles, were separated by flotation centrifugation and identified by electron microscopy.;The lipid particles were determined to be novel organelles and termed tapetosomes. They had patches of triacylglycerols (TAGs). situated among densely packed vesicles, but did not have an enclosing membrane. They contained unique polypeptides identified as oleosins, which were proteins previously known to be associated with seed oil bodies. The genes encoding the predominant tapetosome oleosins, of 45 and 48 kD were determined to be associated with the AA and CC genomes of B. napus, respectively. After lysis of the tapetum cells, specific fragments of the oleosins were retained on the pollen surface, whereas the TAGs disappeared completely. The anthers, presumably the tapetum, contained an active alkaline lipase that could hydrolyze the tapetosome TAGs.;The plastids were termed elaioplasts, in recognition of their high contents of nonphotosynthetic neutral lipids. They were enclosed by double membranes, and contained numerous lipid globuli. They possessed neutral esters and unique polypeptides. The neutral esters were identified as steryl esters with mostly saturated fatty-acyl moieties. The elaioplasts also contained a high proportion of monogalactosyldiacylglycerols. After lysis of the tapetum cells, the steryl esters but not the polypeptides of the elaioplasts were recovered from the pollen surface.;In maize (Zea mays L.), a wind-pollinating species, the pollen coat contained a major protein of 35 KD. The protein in its native form was purified to homogeneity and characterized to be an endo-xylanase. It has the highest activity at pH 5 and is most active on oat spelt xylan. |
