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Narumi Matsuda*, Kanji Isuzugawa, Mei Gao, Tadashi Takashina and Koichi Nishimura

The transformation of pears such as `Conference', `Doyenne du Comice' and `Passe-Crassane' has been attributed to the high regeneration frequency from leaf discs (71% to 97%; Leblay et al. 1991). However, it has been difficult to transfer desirable genes into cultivars with low-regeneration frequency such as `Silver bell' (35.4%) and `La France' (10.7%), which are the two major pear cultivars in Japan. In this study, we developed an Agrobacterium-mediated transformation system for `Silver bell' and `La France'. For `Silver bell', leaf discs derived from in vitro shoots were used as explants. The antibiotics for selection of transformants and elimination of Agrobacteria were investigated. In the most optimum condition, which is 30 mg·L-1 Kanamycin and 500 mg·L-1 Sulbenicillin, a 3.2 % transformation efficiency was obtained. However, no success was recorded in an effort to transform `La France' using leaf disc explants because of very poor regeneration frequency. Therefore, axillary shoot meristems were used as explants for transformation of `La France'. The conditions for antibiotic selection and elimination of Agrobacteria were also investigated. In 5 mg·L-1 Kanamycin and 375 mg·L-1 Carbenicillin, transformed shoots were produced at 4.8% efficiency. No chimera was observed in the transgenic shoots during a 2-year subculture period. Since the inoculated explants developed into multiple shoots during selection, it was thought that the problem of chimera might have been overcome. Therefore, this transformation method using axillary shoot meristem may be applicable to pear cultivars recalcitrant to regeneration from leaf disc. To the best of our knowledge, this is the first report of a transformation system in pear cultivars with low regeneration efficiency.

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Akira Sugiura, Yoshiko Matsuda-Habu, Mei Gao, Tomoya Esumi and Ryutaro Tao

In persimmon, plant regeneration from cultured cells usually takes place through adventitious bud formation. If somatic embryogenesis were possible, the efficiency of mass propagation and genetic engineering would be greatly improved. We attempted to induce somatic embryogenesis from immature embryos and plant regeneration from the induced embryos. Hypocotyls and cotyledons from immature ‘Fuyu’ and ‘Jiro’ seeds were cultured in the dark in Murashige and Skoog medium solidified with gellan gum and supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BA) at various concentrations. Callus formation started at ≈2 weeks of culture, and the callus formation rate was highest at 3 or 10 μm combinations of 2,4-D and BA. The initially formed calli gradually became brown or black from which white embryogenic calli (EC) appeared secondarily. After ≈8 weeks of culture, globular embryos were formed from these EC, and the formation proceeded until 20 weeks of culture. Formation of globular embryos was higher with ‘Fuyu’ than ‘Jiro’, especially with hypocotyls. When EC with globular embryos were transferred to fresh medium with no plant growth regulators, ≈70% developed to the torpedo-type embryo stage in 6 weeks. The torpedo-type embryos thus formed were germinated and rooted in agar medium with or without zeatin in several weeks without entering dormancy. After germination and rooting, the plantlets were transferred to the same medium and acclimatized for another 4 weeks. As the embryos germinated and rooted simultaneously, the plantlets were easy to grow in pots without transplanting shock. This is the first report on plant regeneration through somatic embryogenesis of persimmon.

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Li-Hong Gao, Mei Qu, Hua-Zhong Ren, Xiao-Lei Sui, Qing-Yun Chen and Zhen-Xian Zhang

Single-slope, energy-efficient solar greenhouses in China use solar energy as the sole source of light and heat for winter crop production in the region between latitudes 32°N and 43°N. The use of solar greenhouses has greatly reduced energy demand and carbon dioxide (CO2) emissions. Solar greenhouses are the best structure for growing winter horticultural crops in China, and have been adopted by countries such as Japan, Korea, and Russia. Increased proliferation of efficient solar greenhouses in China may contribute to solving worldwide problems such as the energy crisis and global climate change. This article summarizes the structure, function, application, and ecological benefits of energy-efficient, single-slope solar greenhouses in China, based on 20 years of systematic studies. We hope this technology can be applied to regions of similar climate to help reduce energy consumption and CO2 emissions.