Influencing factors to seed dormancy and germination characteristics of Sorbus pohuashanensis were studied. These factors included the morphological development of embryos,the mechanical obstruction of the seed coat,the water and air permeability of seed coat,and the biologic inhibition of extracts from different parts of seed. The results showed that when the seeds of Sorbus pohuashanensis became mature,the morphological development of the embryos was complete. The influencing effect of the mechanical obstruction,the water and permeability of seed coat for seed germination was little; there were inhibited substances to the seed of cabbage germination in seed coat and embryo,the germination depressor could be fat soluble substances. This indicated that the dormant degree was different for the different embryo parts. Cotyledon and hypocotyl was in low degree dormancy,whereas radicle and epicotyl was in high degree dormancy. To some extent,the germination rate of in vitro cultured embryos was increased with detruncating cotyledon and radicle treament. A 1∶3 mixture of seeds and sharp sand at low temperature in favor of removing dormancy. Treated by 200 mg·L -1 6-BA for 24 h,then remained in low temperature (0～5 ℃),seeds could germinated well (the germination rate could reached 31.56% in 3 month treatment). ABA completely inhibited the germination of seed,warm-cold varied temperature treatment did not promote the removing of dormancy of seed.
Maturing seeds were collected from fifty-year-old trees of Fraxinus mandshurica. The cotyledon and hypocotyl zygotic embryos were excised and cultured on 1/2MS media to induce somatic embryos. In cytological study of embryo development, by the way of paraffin, somatic and zygotic embryogenesis was observed and compared under light microscope. The results showed that somatic embryos from zygotic cotyledons originated directly from single epidermis cell. The somatic embryos that indirectly occurred on the embryogenic callus came from its singular surface cell or internal multi_cells. There was an obvious cytological difference between embryogenic and non-embryogenic callus. Somatic and zygotic embryogenesis underwent the similar course, passing through proembryo, heart, torpedo and cotyledonary stages. The important differences in morphogenetic process exited as following: volume of somatic embryos was smaller than its partner at the same development stage; somatic embryos had no obvious suspensors; somatic embryos showed morphologic variations.
