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Takuro Suyama, Kunio Yamada, Hitoshi Mori, Kiyotoshi Takeno and Shohei Yamaki

A cDNA library was constructed from poly(A)+RNA extracted from pollinated fruit of `PMR-142' cucumber (Cucumis sativus L.). Subtraction hybridization was made between the cDNAs and poly(A)+RNA from unpollinated fruit to isolate cDNA clones that corresponded to the genes preferentially expressed in the pollinated fruit. We isolated three cDNAs, which were 756, 826, and 998 nucleotides long and designated Csf1, Csf2, and Csf3, respectively. When fruit growth was triggered by pollination, auxin treatment and natural parthenocarpy, Csf2 was always expressed. Time course of expression of the Csf2 gene was nearly parallel to that of the fruit growth. Nucleotide sequences of the Csf cDNAs were fully determined. Homology of the deduced amino acid sequence for Csf1 showed 75% identity with a pea extensin. Only 37%, 33%, and 26% homology was found between Csf2 and bell pepper CaSn-2, tobacco FB7-4, and opium poppy gMLP15, respectively. The Csf3 sequence showed 68% identity with the large subunit of 60S ribosomal protein L3 of Arabidopsis thaliana.

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Keiko Sekido, Yusaku Hayashi, Kunio Yamada, Katsuhiro Shiratake, Shogo Matsumoto, Tsutomu Maejima and Hiromitsu Komatsu

We have used a red-fleshed apple cultivar, Malus ×domestica Pink Pearl, and its progeny, ‘JPP 35’, as paternal parents for producing new red-fleshed cultivars suitable for fresh use or processing such as pie fillings, dried apple, apple juice, or cider. In this process, we found that the S3-RNase allele of ‘Pink Pearl’ was linked to its red flesh trait. It was suggested that this trait might be controlled by a new gene apart from the MYB10 (MdMYB10) gene. Using ‘JPP 35’ (S-RNase allele genotype; S3S7) produced by ‘Jonathan’ (S7S9) × ‘Pink Pearl’ (S3Sx) as a paternal parent, we developed a system for producing red-fleshed progenies suitable for fresh use. That is, 96% and 86% of progenies from ‘Shinano Sweet’ (S1S7) × ‘JPP35’ (S3S7) and ‘Orin’ (S2S7) × ‘JPP35’ (S3S7) containing the S3-RNase allele, respectively, showed the red flesh trait. Similarly, red-fleshed progenies suitable for apple pie or natural red juice could be produced by ‘Jonathan’ (S7S9) × ‘JPP35’ (S3S7).

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Motoko Iida, Nancy A. Bantog, Kunio Yamada, Katsuhiro Shiratake and Shohei Yamaki

The regulation of NAD+-dependent sorbitol dehydrogenase (NAD-SDH, EC by sugar was investigated by using sliced tissues of japanese pear (Pyrus serotina Nakai cv. Kousui) fruit in order to determine its role in the mechanism of sugar accumulation in fruit tissue. The results of the activities and steady-state levels of the protein and mRNA indicate that NAD-SDH in japanese pear fruit is among the sugar-inducible genes. By preincubating the sliced tissues for 16 hours in a medium without sugar, NAD-SDH activity declined and reached a stable level that was maintained for up to 40 hours. The washing procedure also reduced the sugar concentration in the apoplast and cytosol of the sliced tissues to low concentrations and enabled them to be manipulated by exogenous applications of carbohydrate solutions. Incubation of tissues in 50 or 100 mm sorbitol for 8 hours led to enhanced expression of the NAD-SDH gene as determined by increased mRNA and protein levels and enhanced enzyme activity. The presence of 100 mm glucose, sucrose, or mannitol also gave significant stimulation on the levels of activity, protein, and mRNA of NAD-SDH compared with those of control tissues bathed in media in which the osmotic potential had been adjusted to that of the sugar solutions by adding polyethylene glycol. However, fructose was ineffective in stimulating NAD-SDH activities and the level of the protein was not enhanced but the level of mRNA was increased. Therefore, it is suggested that NAD-SDH gene transcription is enhanced by each sugar investigated, and fructose appears to be unique as it also influences NAD-SDH at a post-transcriptional level.