Abstract: It has long been known that the developing pollen grains and tapetal cells within the maturing anther pass through what appear to be opposing phases of metabolism. The tapetal cells, which are initially in a stage of active synthesis, gradually pass into a phase of decline and senescence, while the pollen grains continue to develop and differentiate. There are, however, important differences in the timing and extent of these events, particularly when a comparison is made between the secretory and periplasmodial types of tapetum. During the tapetal senescence, it is tacitly assumed that some of the degradative products of the tapetal tissue are utilized by the maturing pollen grains. The bulk of the sporopollenin in the anther is found in the pollen grain walls. During the early phases of development, when the pollen grains are enveloped by an impermeable callose wall, the sporopollenin is most certainly formed from precursors located within the pollen grain cytoplasm. Following the dissolution of the callose layer and the release of the microspores into the anther cavity, there is a bulk deposition of sporopollenin on the pollen grain wall. Small pores in the furrow region would appear to provide a route through which soluble precursors could pass into the pollen grain cytoplasm. The tapetal cells of some plant species form Ubisch bodies (orbicles) which are released into the anther cavity. The precursors of these bodies are formed in embayments of the endoplasmic reticulum which are a characteristic feature of the tapetal cytoplasm at this stage of development. Similar profiles of endoplasmic reticulum are also seen in the tapetal cytoplasm of those species which do not form Ubisch bodies. There is a close correlation between the time of bulk sporopollenin deposition in the pollen grain wall and the appearance of Ubisch bodies at the surface of the senescing tapetal cells. Polymerized sporopollenin is only rarely found within the cell cytoplasm and is characteristically deposited outside the cell membrane. This deposition appears to be centred on thin electron transparent lamellae, which may represent either a synthetic site for the polymerization of soluble precursors or a passive framework on which the sporopollenin is deposited. Although both developing microspores and senescing tapetal cells have the ability to synthesize sporopollenin, it is only in the wall of the former that it is deposited in a regular and reproducible manner.

Abstract: SUMMARY A description and discussion are given of the morphological changes of the cell organelles during the middle and late tetrad stage and the young microspore of Pinus sylvestris with special reference to the pollen wall formation. In the middle tetrad stage the template of the pollen wall pattern appears to be the result of Golgi material excretion and callose wall formation. The fine fibrillar material from the content of the Golgi vesicles, consisting partly of a polysaccharide, forms the primesexine. During the late tetrad stage the sporopollenin originates from the microspore and is deposited on membranes mainly outside the cell. It penetrates into the primesexine. The starch in the plastids disappears and the lipid granules become voluminous; both elements are related to the pollen wall formation. The swelling of the sacci may be an osmotic process. From the quantitative approach it appears, that the young microspore contains approximately one fourth of the number of cell organelles present in the cell during zygotene. The cell organelle population probably does not change in number during the meiotic stages. A general survey summarizes the whole process of microsporogenesis till the young microspore stage. The control of pollen wall formation is also discussed.

Abstract: SUMMARY After zygotene the tapetal cell becomes osmiophilic. The electron density of the cytoplasm decreases during the early tetrad stage and increases afterwards. During the young microspore stage the tapetal cell degenerates. The electron density of the cytoplasm is caused mainly by the high content of ribosomes. From interphase II onwards the tapetal cell starts to produce sporopollenin. In the cytoplasm pro-orbicular bodies are found. The formation of orbicules seems connected with the endoplasmic reticulum and ribosomes. Outside the cell the sporopollenin appears around the orbicules and as a pollen sac against the cell wall of the endothecium cells. The electron dense globules on the plasma membrane may be related to the formation of sporopollenin.

Abstract: Chromosomal associations in a triploid indica rice plant (T. 1242) at meiosis were investigated.Majority of metaphase I cells showed chromosomal association of 10III+3II. Precocious disjunction was observed in non-homologous bivalent and moved to opposite poles. The third chromosome of each trivalent separated first and moved irregularly to the poles.Majority of the anaphase I cells recorded 19/17 disjunction followed by 18/18 and 20/16. Fifty percent of the cells showed 1 to 5 laggards at telophase I.Triploid plant exhibited high percent of spikelet sterility and pollen abortion. There seems to be a close relationship between the number of microspores with micronuclei and the pollen sterility; more the micronuclei, greater is the pollen sterility.

Abstract: Publisher Summary This chapter discusses the histochemistry and ultrastructure of pollen development in Podocarpus macrophyllus D. Don. In the early stages of development of the microsporophyll, the cells are rectangular with a profusely vacuolated cytoplasm and numerous amyloplasts and plasmodesmatal connections are present. During prophase, the tapetal cells are characterized by abundant ribosome and polysome populations, amyloplasts, and Golgi activity. As the plasmalemma of the microspore mother cells withdraws from the parent wall, mildly PAS-positive fibrillar material remains, presumably a breakdown product of the original wall. Long, thin, three-layered structures of an intensely electrondense material appear in the cytoplasm of the microspore mother cells in early meiosis. The tapetal nuclei and cytoplasm show signs of intense activity from meiosis II until after tetrad formation. The line of demarcation between the distal face of the grain and the air-sacs is markedly different in sculpturing from the rest of the pollen surface, bearing a number of thick finger-like processes.

Abstract: Publisher Summary This chapter discusses the production of haploid embryos from pollen grains. Extensive trials with both Nicotiana tabacum and N. sylvestris have shown that the most important point in the technique is to excise stamens at the proper stage of development. The crucial stage occurs at the moment microspores are nearing the first mitosis. This stage can be recognized from the development of the petals in the floral bud. Iron-deficiency in higher plants is known to bring about an abnormally high level of arginine. The production of free embryos in large quantities will enable embryologists to experiment more conveniently than hitherto.

Abstract: Publisher Summary This chapter discusses surface membrane specializations and the pollen wall. After meiosis, the four microspores of Nelumbo become separated by a callose-containing wall continuous with the special cell wall. Thiocarbohydrazide (TCH), a multidentate ligand, binds to certain cations found in thin sections of biological material. When microspores of Nelumbo in the tetrad stage are treated with PA-TCH-Pro, the fibrous wall gives a positive response, as do restricted areas on the plasma membrane, small vesicles in the cytoplasm, and distal cisternae of dictyosomes. The microtubules of Aegiceras have a similar diameter to the wall microtubules in Nuphar, but they are found on the exine surface and the locular surface of tapetal cells. A plug of polysaccharide is found in the aperture of Impatiens after the microspores are released from the special cell wall.