| Hickory (Carya cathayensis Sarg.) is a deciduous tree belonging to family Juglandaceae. It is a commercially and ecologically valuable tree and is likely to become one of the world's energy trees. The species has been extensively cultivated and used in wild or semi-wild state. At present, seed, grafting and cutting are the important conventional propagation measures. But conventional propagation is not sufficient to satisfy the progressive demand. Therefore, there is an urgent need to develop protocols for rapid propagation of hickory through tissue culture, which will be useful for propagation and conservation. The aim of this research is assessing the development characters of immature embryos, somatic embryogenesis and histocytological study of differentiation of somatic embryos. The results are as follows:1. Development character of immature embryo was studied. The result showed that the development of immature embryo goes through globular, heart-shaped, torpedo and cotyledonary phases. The changes of endogenous hormones in the immature embryos which 8 to 16 weeks after open pollination was determined by ELISA. The results indicated that the contents of GA3 and IAA promoted with the development of the immature embryo. The contents of GA3, IAA and ABA of immature embryos 14 weeks after open pollination were up to 11.3 ng·g-1FW and 128.9 ng·g-1FW respectively followed by a decrease. The content of ZR of immature embryo gradually increased up to 19.2 ng.g-1FW then followed by a decrease. The content of ABA of immature embryo continuously increased up. The embryogenic response of immature embryos 8～10 weeks after open pollination was good. The immature embryo of this phase was easily to dedifferentiation. Somatic embyrogenesis was easily derived from the immature embryo which was 11～12 weeks after open pollination. While the immature embryo was easy to germinate when the immature embryo 13～14 weeks after open pollination.2. An efficient plant regeneration protocol was achieved via in vitro germination and somatic embryogenesis from immature embryo. In this study, the effects of basal medium, plant growth regulators, carbon sources and other culture conditions on callus induction, somatic embryogenesis and in vitro germination were investigated. Indirect somatic embryogenesis was induced from immature embryo 8～10 weeks after open pollination. The results indicated that the optimal media for indirect somatic embryogenesis was half strength of MS supplemented with 1.0mg·L-1BA,0.01 mg·L-1 Picloram,0.5 g·L-1 CH,20 g·L-1 glocuse and 8.0 g·L-1 agar type, pH 5.7. Additional transfers to fresh medium were done at 4-week intervals.Direct somatic embryogenesis was induced from immature embryo 8-10 weeks after open pollination in dark room at 30℃. The results showed that optimal media was modified WPM (WPM minus glycine) supplemented with 1 mg·L-1BA,1.0mg.L-12,4-D,30 g·L-1 sucrose,6.0 g·L-1 phytgel, pH 5.7. Additional transfers to fresh medium were done at 2-week intervals. The frequency of somatic embryogenesis was up to 36.5% after 6 weeks of transfer.In vitro germination was occur from immature embryo 8-10 weeks after open pollination. The result showed that MS supplemented with 2.0 mg.L-1 BA, 0.01mg.L-1 piclaram.30 g·L-1 glocuse,8.0 g·L-1 agar type A, pH 5.7. The explants cultured in dark a week followed by light condition. The frequency of germination was 90.3%.3. Histocytological research was carried out to study somatic embryogenesis of hickory. The result indicated that somatic embryos derived from the surface of cotyledon and hypocogyl of the immature embryos. Mature somatic embryos developed from globular, heart-shaped, torpedo and cotyledonary somatic embryos.
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