Distribution Of Calcium, Polysaccharides And Lipids In Developing Anthers Of Ipomoea Cairica (L.) Sweet

The distribution of calcium,polysaccharide and lipid in developing anthers of Ipomoea cairica(L.) Sweet was studied by using potassium antimonite technique and histochemical staining technique.The surface characteristic of the microspore and pollen was also observed by using scanning microscope.The results are as follows:(1) From the observation of transmission electron,it was found that there were two middle layers in the anther wall and the inner middle layer cells degenerate at the bicellar pollen stage in the developing anthers of I.cairica(L.) Sweet.The tapetum cells were dimorphic and dual origination:the connective tapetum(C-tapetum) is derived from the cells of the connective,and the parietal tapetum(P-tapetum) from the parietal cells.The C-tapetum was formed at the stage of microspore mother cell, and the P-tapetum at the stage of sporogenous cell.The process of pollen wall formation was also observed using transmission microscopes.Tetrad microspore began to form its primexine,and late microspore form its intine.The pollen exine could be divided into three layers:tectum,baculum and endexine.At the bicellular pollen stage,the intine and exine continued to develop, and the pollen inclusion gradually increased,which led to the obviously enlarging volume of pollen.(2) From the observation of distribution of calcium in the developing anthers, many calcium precipitates appeared in the cytoplasm of sporogenous cell.Then the precipitates moved into the callose wall of microspore mother cells.At the tetrad stage, many calcium precipitates were still in the callose wall,which concentrated in the primexine of the microspore wall.During microspore development,calcium precipitates were mainly located in vacuoles and pollen wall.In forming pollen wall, many big calcium precipitates were distributed in the ectexine and intine,but a few in the endexine,and then the precipitates in endexine disappeared in late microspore.At the bicellular pollen,calcium precipitates were only found in ectexine.From the calcium distribution,it could be speculated that calcium might play several roles in pollen development,for example,in the formation and disintegration of callose wall, in large vacuole formation and in pollen wall construction.Many calcium precipitates were in the anther wall before the microspore mother cell stage.The precipitates were mainly located on the edge of the vacuoles and in the cytoplasm and cell wall of endothecium,middle layer and tapetum.However,in epidemic ceils,the precipitates only appeared in the vacuole.From the tetrad stage to the late microspore stage,calcium precipitates in anther wall slightly decreased.After the bicellular pollen stage,calcium precipitates further decreased.In tapetum cell,before the degeneration of tapetum,calcium precipitates were deposited in the cell wall.After the tapetum degeneration,some small calcium precipitates deposited in the cytoplasmic remains.The calcium precipitates were found on the surface of the tapetal Ubisch body.During anther development,some calcium precipitates were always found in the cell wall,in the vacuole and on the edge of the vacuole in the connective cells,but in the bicellular pollen stage,it decreased rapidly.It could be inferred that in the early stage of anther,calcium was transported to anther wall cells by connective tissue.Between the stage of microspore mother cell and the late microspore stage,calcium was transported to anther chamber.The Ubisch bodies,on whose surfaces some calcium precipitates deposited,could transport calcium to the callose in the disintegration tetrad,to the microspore primexine and the pollen wall.After the bicellular pollen stage,because the demand for calcium decreased in pollen grains,calcium precipitates were mainly found in the exine.(3) The distribution of polysaccharides and lipids in the developing anther were checked using histochemical staining techniques.Some polysaccharides accumulated in the sporogenous cell.However,before the meiosis of microspore mother cell (MMC),the polysaccharides in the MMCs disappeared and some small lipids appeared in the cells.After the meiosis of MMCs,lipid drops disappeared and polysaccharides appeared again in tetrad microspores.In later microspores,a large vacuole formed and lipids appeared again.After microspore mitosis,the large vacuole disintegrated and many polysaccharides and lipids accumulated in bicellular pollen grains.At anthesis,the mature pollen grains were filled with plenty of polysaccharides and lipids as storage nutrition.During anther development,there were some polysaccharides first appearing in the epidermal cells of anther wall at the sporogenous stage and then in the endotheciumal cells at microspore mother cell stage.After that,more polysaccharides and a few lipids were always found in the epidermis and endotheciumal cells.Before tapetum degeneration,no polysaccharides accumulated in the tapetal cells except a few small lipids.At early microspore stage,tapetal cells degenerated.In early bicellular pollen stage,inner middle layer degenerated and its cytoplasm remains were transformed into many lipids.According to the results,the polysaccharides and lipids in anther displayed some functions in anther development:before bicellular pollen stage,the accumulated polysaccharides might be related with the syntheses of callose wall of MMCs and pollen intine.The lipids might be related with syntheses of vascular membrane and pollen exine.After bicellular pollen stage,developing pollen needed to store plenty of polysaccharides and lipids,which would provide power and materials in the development of generative cells and the process of pollen germination.