Studies On Changes Of Plant Hormone Content And Tissue Structure During Growth And Development Of Seed In Ginkgo Biloba L.

In this study, the bearing trees from Fozhi, the seed-purpose leading cultivar of Ginkgo biloba L., were used as materials to take a treatment of pollination, and to investigate effects of pollination on the percentage of fruit setting, then to periodically take ovules and seeds for determinating the single grain weight, length and width of seed, and for observing the changes of the tissue structure and cell and their differences during development from ovule to seed after pollination by paraffin section, semithin-sectioning and electric microscope scanning etc., and for detecting the content changes of endogenous hormones and their differences of distribution in seed during growth and development of seed by ELISA. The results indicated as follows:1. The average percentage of fruit setting after pollination was 93.3 %, and was 43.3% higher than that of no pollination, so it is a key for using pollination to increase the percentage of fruit setting to seed-purpose cultivar in Ginkgo biloba L..2. In female plant of Ginkgo biloba L., the nucellus and integument of ovule divided until pollinating when the macrospore mother cell in centre of nucellus divided into a megaspore tetrad after meiosis, of which one macrospore produced the free nuclei of female gametophyte after mitosis.When the free nuclei formed cell wall, the female gametophyte began a development of multicellular stage until formed endosperm including more amyloplasts. Near micropyle, the archegonium stood on the top of the female gametophyte, at the same time, the pollen chamber formed after disintegration of some cells. After pollination, the pollen entered in the micropyle and then came in the pollen chamber along chalaza of nucellus to germinate and form pollen tube, at last came in the archegonium for fertilization.3. In the ovule of Ginkgo biloba L., the integument was rapidly growing and PCD( Programmed cell death) appeared at the top and end of nucellus at the 10th day after pollination, i.e. on 25th April; on May 15, the cells of integument began differentiating, the external integument became an exotesta, the meso-layer of integument became a mesosperm, and the internal integument became an endopleura; on June 5, the secretory cavity of endopleura developed mature and PCD of mesosperm started up; on June 25, the cell wall of mesosperm was luther thickening, the chromatin in which concentrated heavily; on July 5, the nucleus in Which became as a budding-like or constriction-like;4. With growth and development of seed, its tissue structure was differentiating and the cell shape of which was correspondingly varying. At the 15th,30th,45th and 60th day, the coefficients of variation for the exotesta, mesosperm and endopleura were bigger,so the differences of the ratioes of length to width of cell in different tissue structures at the same stage after full blossom were significant or much significant. The ratioes of length to width of cell in the same tissue structure were decreasing until the 45th day after full blossom, then began increasing, which showed that the morphological development of cell in different tissue structures was out of step.5. The accumulating growth of length, width and single grain weight of seed showed as a sigmoid curve, the main growth periods of which was 40d, 42d and 87d, the initial date of vigorous growth of which was 15d, 13d and 23d after full blossom, the vigorous growth date was 28d, 28d and 51d after full blossom, the end of vigorous growth of which was 55d, 55d and 100d after full blossom, respectively.6. When the ovule emerged and had been growing for 17 days, its content of IAA and ABA began obviously increasing, the ovule grew until the 27th day when the content of GA began obviously increasing. The emergence time for the first peak of IAA content in ovule, the 47th day after ovule appearance, was corresponding to that of GA. The emergence time for the first peak of ABA content in ovule, the 27th day after ovule appearance, was earlier than that of IAA and GA. The maximum content of IAA,GA and ABA in ovule was 4.67pmol/g·FW,4.62pmol/g·Fw and 1.95pmol/g·FW, respectively.In the exotesta, the emergence time of the maximum content of IAA, the 87th day after ovule appearance, was corresponding to that of both GA and ABA, the content of which was 12.99pmol/g·FW,11.37pmol/g·Fw and 5.02pmoi/g·FW, respectively. Following the ovule growing for 47 days, the contents of IAA,GA and ABA in kernel began decreasing in different degrees, of which the content of IAA was down until the 67th day after ovule appearance, then trended to steady until seed ripening, the variation of GA and ABA's content had a slight ups and downs.7. The content of IAA , GA and ABA in exotesta, was 3.37pmol/g·FW,7.67pmol/g·Fw and 1.94pmol/g·FW, respectively, was higher than that in kernel, the differences of which were significant or much significant. In the exotesta, mesosperm and endopleura, the contents of IAA and GA were higher than that of ABA. The content of GA in ovule at one day after pollination was significantly lower than that at one day before pollination. Between above both pollination treatments, there was any insignificant difference for the IAA and ABA contents in ovule. After pollination the differences of IAA , GA and ABA contents in ovule were significant until the lignification of mesosperm, after which, the differences of IAA, GA and ABA contents in exotesta and kernel at different stages were significant or much significant until seed ripening.8. The changes of contents in ovule, exotesta and kernel were corresponding to that of growth and development for cell and seed. When the contents of IAA and GA were obviously increasing, the growth of cell width of integument sped up, the seed began remarkable growing, the macrospore mother cell started up a meiosis, from which the macrospore divided to free nuclei of female gametophyte. When the annual maximum contents of IAA, GA and ABA appeared, and the seed was vigorously growing, and the integument was obviously differentiating, the external integument developed to an exotesta in which there was a lot of secretory cavities, the meso-layer of integument developed to a mesosperm, the female gametophyte began a development of multicellular stage, the endosperm formed, the number of amyloplast in thin-walled cell was increasing, which was ready for coming of the end of vigorous growth of seed.