Seed Biology And Somatic Embryogenesis Of Sorbus Pohuashanensis

Sorbus pohuashanensis is an valuable ornamental and economic small tree species in thefamily of Rose distributed in northern China. The seed biology and somatic embryogenesis ofit were systemmaticly studied and the research findings areas follows:(1) There were abundent phenotypic variations for fruit and seed of S. pohuashanensis, and thevariations in a collecting site were bigger than those among collecting sites.Fruit length and diameter were the key phenotypic characters for fruit, and Seed lengthand width were the key phenotypic characters for seed. Seed phenotypic variation showed aone-way variation along latitude. There was significant variation among individuals for 1000-seed weight and seed vitality, and it could not changed by air-tight cold storage. There wassignificant variation among collecting sites for initiation time ofseed germination andsignificant variations between individuals in a collecting site for seed germination percentageand germination index.(2) Physiological factors was the main cause for dormancy of S. pohuashanensis mature seeds,and.cold stratification at 2-5 degrees centigrade was favorable to dormancy removing of S.pohuashanensis mature seeds.There was no significant changes for fruit shape of S. pohuashanensis from 105 days afterpollination. Zygotic embryo develops to cotyledon stage in 30 days after pollination. Therewere no significant changes for the length/width ratio and moisture content of zygotic embryosfrom 75 days after pollination, indicating that the zygotic embryos has step into the stage ofphysiological maturity. Seed coat is an important restricting factor for germination of seed indeveloping. Soaking treatment and low temperature were favorable to germination of matureseed. High ABA content in seed coat and embryo was the main. restricting factor for seedgermination of S. pohuashanensis. Drying process of seeds before stratification significantlyenhances the GA₃/ABA ratio in seed coat and embryo that was favorable to seed germination.Cold stratification strikingly influenced endogenous hormone content and balance of S.pohuashanensis seeds, and this significantly decresed ABA content in seed coat and.notablyincreased the relative content of growth-promoting substances (especially GA₃/ABA ratio).cold stratification at 2-5 degrees, centigrade was favorable to dormancy removing of S.pohuashanensis mature seeds. Air-tight storage at low temperature had significant effect onseed vitality. Dormancy-removed seeds could germinate at 5℃～25℃. In this temperaturerange, seed germinate percentage increase with the increase of temperature, but no seedsgerminate at.30℃. The germination percentage and index was higher for dormancy-removedseeds at 5℃and 10℃but germination initiated late. (3) Treatments by BA, KNO₃ and high-voltage electrostatic field could promote seedgermination, but KNO₃ treatment was most suitable for application in production.By soaking in 200 mg·L^-16-BA and then storing at 25℃for the first 10 days and at 5℃for the remaining days, the germination rate, timing and uniformity were greatly improved.Effect of GA₃ on seed germination is not significant. Long time treatments of ABA inhibit seedgermination. Treating by KNO₃ solution to process seed of S. pohuashanensis has the featurethat is more operational, strikingly effective, pollution-free and easy-spreading. Combinedtreatment of electrostatic field and cold stratification significantly increased the seedgermination percentage as well as enhenced stress tolerancyof seedlings of S. pohuashanensis.(4) Somatic embryogenesis was obtained by using both immature and mature zygotic embryosof S. pohuashanesis as explants and emblings were obtained.The most suitable period for explant collection of somatic embryogenesis of S.pohuashanesis is 30 to 60 days after pollination. Embryos collected in 30 days afterpollination is very sensitive to plant growth regulators and result in fast, highest-percentagesomatic embryogenesis. Highest induction rate was obtained on medium containing 1 mg·L^-1NAA (66.9%) or 0.5 mg·L^-1 2, 4-D (63.3%). Combination of BA and NAA or 2,4-D couldstimulate the induction of callusand increase the number of somatic embryos as well. 40 g·L^-1sucrose was suitable for induction of callus and somatic embryos. Somatic embryogenesis canobtained directly or indirectly for S. pohuashanesis, but main pattern was direct. Thedeveloping stages cover globular, heart, torpedo and cotyledon embryo stage. Mature somaticembryos could germinate on MS medium, the germination percentage and emblinggeneneration rate could reach 38% and 10% respectively. Lower-salt medium and lower levelof NAA promoted rooting. 90% of rooting was obtained when cultured in 18℃for 50 days.(5) Secondary somatic embryos of S. pohuashanesis developed well and could be a good formfor practice utilization.Secondary somatic embryos was induced on MS medium supplemented with 0.01mg·L^-1of NAA, and the proliferation percentage was highest on medium supplemented with 0.05mg·L^-1NAA and 200 mg·L^-1 CH. Highest number of mature somatic embryos were obtainedwhen the embryos were culture under strong light on medium containing 12μmol·L^-1ABA, 20g.L^-1sucrose and 75 g·L^-1PEG. MS medium was.more suitable for germinating than 1/2MSmedium. Subcultured at every other 30 days helped to retain the embryonic potential for allyear long.(6) Cell division in embryonic cells was similar to that of zygotic embryos, and there issuspensor on somatic embryos of S. pohuashanesis.The first division Was un-equalized division, and then embryonic cells developed fromradiate symmetry to two sides symmetry. There is suspensor on somatic embryos induced from surface cell on zygotic embryo or callus. Histological analysis showed that many PCD cellssurround the early multi-cell proembryo.Through above research, (1) Making clear of dormancy reason of S. pohuashanesis seedsand developed a effective new method for increasing seed germination percentage that issuitable to production application; (2) Established a relative satisfactory somaticembryogenesis system for the first time; (3) Proposed a new way of establishing secondarysomatic embryogenesis system by taking primary somatic embryos as explants, so that toobtain synchronously developed, even germinated and highly regenerated emblings.