Studies On The Cytological And Histological Of Somatic Embryogenesis In Hevea Brasiliensis

The technology of plant tissue culture could be considered as a junction connecting the plant biology with the plant genetic engineering and also as an important research field in modern crop cultivation. The study on cytobiology of somatic embryogenesis could provide an important theoretical foundation for improving the technology of plant tissue culture.The technique of somatic embryogenesis in Hevea brasiliensis was succeeded in 1970s. But now the technique was dropped behind because that so far, only a few the clones could produce somatic embryogenesis through this technique, and the rate of the in vitro plant regeneration in most of the clones was very low. This became the main obstacle in the way to found the high genetic transformation system for reconstructing the inheritance of Hevea in molecule level. Moreover, a few of studies were involved on the histology and cytology of in vitro morphogeny in the past days. It was studied that the process of the somaticembryogenesis and analyzed that the problem existing in technique of in vitro morphogeny in Hevea to ground for that to probe into the method to improve the technology of tissue culture in Hevea with the techniques of transgene and to improve the ability of somatic embryogenesis and plant percentage of embryoid in Hevea. The result of this study also could enrich up the data for theory of the somatic embryogenesis of plant and provide histological foundation for the using of embryonic callus tissues as transformational receptor.The anthers of Hevea Brasiliensis Haiken 2 were used as explants for inducing the somatic embryoids. The histology was observed that the generating mode and development process of the somatic embryos in Hevea by microscope and analyzed every phase of somatic embryos generating and the cause of formation of abnormal embryos in Hevea. The results were shown as follow.1 Somatic embryos of anther in Hevea generates mainly in indirect mode. The somatic embryos of anther were formed through callus tissue. The somatic embryo originated from single embryonic original cell of embryonic callus tissues, which was surrounded by tannin cells, that belonged to single cell origination. Almost all somatic embryos originated from several layers cells, which near to the external callus, only a few of them originated from the internal callus.2 Somatic embryos in Hevea had bipolarity. There were the radicle polarity and the plumule polarity in differentiation of the first somatic embryogenesis. Polarity also exited in single embryonic original cell, which divided unequally into two cells, one nearing to the external callus was the apical cell, and the other nearing to the internal callus was the basal cell. After that, the apical cell divided vertically respectively to form 2-celled, 4-celled, and multicellular proembryos and developed into globular embryoid, heart-shaped embryoid, torpedo embryoid,cotyledonary embryoid. And the basal cell divided transversely to form suspensor structure, which formed into single line cells in shape and with many lines cells in shape in the period of globular embryoid. When the embryonic original cell divided to form multicellur proembryos, the cell wall of the external cell was thickened to form a clear cell boundary to separate from ambient cells that was a phenomenon of isolation The protoderm began to be differentiated in the period of globular embryoid, and the procambium differentiated clearly in period of torpedo embryoid. Moreover, developments of somatic embryoids were non-synchronous, it could be seen in the same time that single embryonic cell, 2-celled, 4-celled and multicellular proembryos existed in one cutting generally in all process.3 The key period was from heart-shaped embryoid phase to torpedo embryoid phase, during the somatic embryogenesis in Hevea. It was easily to induce to globular embryoid or heart-shaped embryoid, but most of them stayed at this state and could not develop into normal embryoid, such as torpedo embryoid, but abnormal embryoid. Only a few of them developed...