| The paper studied the conditions for somatic embryogenesis of Citrullus lanatus and the factors that affected somatic embryogenesis. Also different phases of somatic embryogenesis were studied thourgh cytological observations. The effects of exogenous hormone on the expreesion level of indogenous hormone were studied by ELISA in order to illustrate their roles in somatic embryogenesis. And the most suitable culture medium for somatic embryo induction was found. The research results were listed as follow:1 The somatic embyogenesis of three different genotype Citrullus lanatus was studied. The results showed that the somatic embryo induction rate of Zhengkang wuzi No.4 reached a ratio of 25%, which was higher than that of Nongda wuzi No.5 and Taiwan xin No.1.2 The cotyledon which was cultured for 6d is the best explants to induce somatic embryo. The somatic embryogenesis of cotyledon had two ways, direct and indirect. The latter was the primary.3 Hormone played a central role in somatic embryo induction. Little callus were induced by 2,4-D alone or combination with 6-BA, all of which were non-embryogenic callus (NEC). The inducing effects of IAA on induction of somatic embryo were much better than that of 2,4-D. Combining with 6-BA, embryonic calluses were induced then differentiated into somatic embryos. A large amount of somatic embryos were induced when 6-BA, KT and GA3 were used together. The induction rate of somatic embryo could be enhanced by added 30 g·L-1 of sugar. Dark treatment was a essential proccess for induction of somatic embryo. Cotyledons were kept in dark for 7d then transferred to a photoperiod of 16 h / 8 h (L/D). It is necessary for cotyledon to be put in dark conditions before somatic embryo was induced.4 MS is the best basic midium for the tissue culture, the suitable media for somatic embryogenesis of three different genetypes of Citrullus lanatus, Nongda wuzi No.5, Taiwan xin No.1 and Zhengkang wuzi No.4, were MS+ 6-BA3.0mg·L-1+...
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