IntheLilium anther a peritapetal andtapetal membrane aremade bythe tapetal cells. During the young microspore stage thepro-orbicules receive a matrix ofmainly carbohydrates similar to thatof the sexine. The plasma-membrane of the tapetal cells forms membrane-like lamellae. During the vacuolization of the microspore the orbicule diameter increases. In the channels made by the endoplasmic reticulum theglobules ofsporopollenin areproduced. Thelipid inclusions accumulate and globules containing carotenoid increase in the plastids. Both elements fuse and form the "Pollenkitt" during degeneration of thetapetal cell. Some sporopollenin globules fuse and form a second generation of orbicules. Thecell of the middle layer next to the tapetal cell contains lipid granules. Theotherfourcells ofthemiddle layer lose their starch at thestage oftheyoung microspore and after mitosis thelipid granules areproduced. Asa source fornutrients intheloculus thestarch of the middle layer cells hasan important function. Aninteraction model isschematically presented.
Stages in the formation and degradation of pollenkitt in the anther of Lilium have been investigated using the electron microscope. This material, which appears to be a complex of lipid and carotenoids, is formed during the autolysis of the tapetal cells by the fusion of lipidic inclusions with globules derived from plastids. Autolysis of the tapetal cells is progressive for it commences with the disintegration of many cytoplasmic components, followed by the breakdown of storage lipids. The plasma membrane maintains its integrity during these events apparently, by proliferation, aiding in the transfer of the products of hydrolysis into the loculus. During the course of lipid breakdown, a striking vacuolar system is formed in the tapetal cytoplasm, presumably containing the products of this hydrolysis. The source of membranes for this system is clearly the lipid globules themselves. The generation of the membrane apparently involves the participation of electronopaque material, possibly enzymic, contained within the lipid globules.
The ultrastructural changes during the microsporogenesis and gametogenesis in Lilium are studied in relation to the surrounding tissues. In this article the development of the microspore and pollen wall is presented. In relation to the increase in pollen volume the nexine is increased but this process is discontinuous. It is concluded that four periods of sporopollenin deposition can be distinguished. The mechanism of exine formation during the young microspore stage is the embedding of sporopollenin on a sexine matrix of polysaccharides, some proteins and osmophilic material. During this period the sporopollenin deposition on membrane-like lamellae takes place on both sides of the exine. During the vacuolated microspore stage globules, containing sporopollenin are deposited on the exine too. After mitosis the "Pollenkitt" also contributes in sporopollenin addition to the nexine and sexine.Folds of the plasma-membrane of the microspore are the origin of the membrane-like lamellae. The pollen storage consists mainly of starch, lipid granules and lipoprotein.
The features of the exine and orbicules in the Li/ium anther were studied by scanning electron microscopy. The changes in the dimensions and shape of the orbicules and the elements of the exine during development are shown to indicate the course of sporopollenin deposition.In the discussion the data obtained are compared with the results of transmission electron microscopy.
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