Study On Reproductive Biology Of Aesculus Chinensis Beg.

Aesculus chinensis Bug. (Chinese Buckeye) belongs to Aesculus Linn. of Hippocastan -aceae, which is deciduous tree.Currently, the research on Aesculus Linn. related to the cultivation production, seed chemical composition and pharmacological analysis, was focus on the analysis of medicinal ingredients and pharmacological effects. In existing data records, it is rare to see the detailed report about the reproductive development of the Aesculus Linn.. By the way of conventional paraffin technique, we have observed the generation process of the microsporogenesis, megasporogenesis, male and female gametophyte, as well as the development of the embryo and endosperm of A.chinensis Bug.. Using the histochemical staining technology, we also observed the development of starch grains in anther. Besides, we observed the morphology of mature pollen by scanning electron microscopy. The results enriched the research about the biological characteristics of A.chinensis Bug., and provide a scientific basis for plant cultivation and increase the seed germinal rate. The results of this research can be summarized as follows:1.Anther development featuresThe development of the anther wall belongs to a basic type.The anther has four sporangia and the mature anther wall comprises an epidermis followed (on the inside) by one layer of the endothecium, 2 or 3 cells of middle layer . and a single-layered tapetum. The epidermal cells always presents during anther development. The cells of endothecium develop fibrous bands when the anther is ready to dehisce for the discharge of pollen. The cells of middle layer are ephemeral and become flattened and crushed by early meiosis in the pollen mother cells. The development of the tapetum is of the secretary type. At the time of the tetrad stage, the tapetum cells began to degenerate and remained a layer of tapetal membrane when the pollen mature.2. Microsporogenesis and male gametophyteThe archesporium occur under the epidermis of young anthers. The meiotic division of mother cell is simultaneous, mostly tetrads tetrahedral arrangement. During the meiosis, pollen mother cells and tetrads are packaged by callose wall. At microspores stage the callose wall gradually disappear. The mature pollen grains are two-cell types and are cylindrical triangular shape with tricolporate.By periodic acid-schiff reagent staining (PAS reaction staining) method, it was found that the starch grains are not accumulated in the anther at the archesporium differentiation stage. In the microspore mother cell stage, a small amont of starch grains appears at the connective tissue and endothecium cells. With the continued development of anther, the number of starch grains which in connective tissue and endothecium cells is gradually growing up. In meiosis stage of the microspore mother cell, starch granules do not appear in tapetum cells but reached a peak accumulation in the connective tissue and endothecium cells. In epidermal cells can be found in a small amount of starch grain. With the forming of single cell pollen, starch grains gradually reduced in the anther walls but began to appear in pollen. To the mature pollen stage, pollen grains accumulated more starch grains.By scanning electron microscope, the pollen grain appears elongated oval-shaped with tricolporate apertures. Pollen grain surface possessed protruding objects.3. Megasporogenesis and female gametophyteThe ovary has 3 chamber and there are two ovules in each one, the ovule is double integuments,crassinucellate and anatropous. The archesporium differentiates immediately below the nucellar epidermis. The archesporial cell divides transversely, cutting an outer parietal cell and an inner sporogenous cell. The latter faunctions as the megaspore mother cell. After meiosis the megaspore mother cell forms four linear megaspore. The megaspore in chalaza end usually is functional one which forms the female gametophyte, whereas the other three degenerate. After three mitotic divisions, the functional megaspore forms mature embryo sac. The embryo sac is of a polygonum type.In mature embryo sac,antipodal cell degenerates early.4. Embryogenesis and endosperm developmentAfter a brief dormancy, the zygote divides transversely, resulting in a small apical cell toward the interior of the embryo sac and a large basal cell toward the interior of micropyle. The division of the apical cell formed globular embryo, heart-shaped embryo and torpedo embryo successively. In the later development, the globular embryo with two internal sides of cell division speeding up, formed the two cotyledons. During the development a diaphragm is formed in the embryo sac and which divided the embryo sac into 2 chamber that is micropylar chamber and chalazal chamber. In micropylar chamber the embryo is formed.The development of endosperm is of the nuclear type. The primary endosperm nucleus was division before the dormant zygote and formed two free nuclei endosperms. The endosperm free nuclei continue to division and formed a circle of free nuclear layer along the embryo sac wall. During seed development, the free nuclei endosperms do not formed endosperm cells and stop to development. So that, the seeds of A. chinensis Bug. belong to exalbuminous.