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  • Author or Editor: Takeo Harada x
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Heterografting experiments were conducted using potato (Solanum tuberosum) as scion and tomato (Lycopersicon esculentum) as stock to test whether an RNA molecule responsible for changing leaf shape can be transported and function across the grafting junction. Results showed that a graft-transmissible RNA from the tomato rootstock without any leaves can indeed change leaf morphology of the potato scion. Therefore, if a transgenic stock plant with acquired RNA transport competence could be constructed, it would provide an effective system for transformation of scion plants. This combination of grafting and RNA transport could provide a novel technique for cultivar improvement in horticultural crops.

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The onset of apple [Malus sylvestris (L.) Mill. Var. domestica (Borkh.)Mansf.] fruit maturity is preceded by the production of ethylene, the ripening hormone, which induces fruit ripening. The amount of ethylene produced by the fruit correlates with the level of transcription of the ripening-specific 1-aminocyclopropane-1-carboxylate (ACC) synthase genes. We have found that an allele (MdACS1-2), which contains an inserted retroposon-like sequence at the 5'-flanking region, is transcribed at a lower level than the wild-type (MdACS1-1). MdACS1-2/2 homozygous fruit produce a lower level of ethylene at the climacteric stage than do the wild type fruit. We have also found that the preharvest drop rates of apple cultivars and strains of MdACS1-2/2 trees have less fruit drop than the MdACS1-1/1 or MdACS1-1/2 trees. Treatment of the MdACS1-1/2 trees with 1-MCP, an ethylene receptor blocker, further decreased fruit drop. Analysis of commercial apple cultivars for the presence of the MdACS1-2/2 allele may help in the early detection of apple cultivars with a low fruit drop rate.

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