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Hideaki Yamaguchi, Yoshinori Kanayama, Junichi Soejima, and Shohei Yamaki

Seasonal changes in the amounts of the NAD-dependent sorbitol dehydrogenase (NAD-SDH) (enzyme code, protein in developing apple (Malus pumila Mill var. domestica Schneid) fruit were determined by immunoblotting analysis. The amounts of the enzyme protein were very low in young fruit and rose as fruit matured. The weak correlation between enzyme protein and NAD-SDH activity and also the changes in NAD-SDH specific activity suggested that there could be posttranslational modification to the pre-existing enzyme or isoenzyme(s) of NAD-SDH. The changes in the amounts of NAD-SDH protein did not show the same pattern as those in relative growth rate, which is used to express sink activity, especially in young fruit. The role of NAD-SDH on sink activity in apple fruit, therefore, could not be explained simply by the amount and activity of the enzyme. In young fruit, it seems that enzymes other than NAD-SDH would be more directly related with fruit growth.

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Akiko Ito, Hideaki Yaegaki, Hiroko Hayama, Shinnosuke Kusaba, Isomaro Yamaguchi, and Hirohito Yoshioka

Flower development of the lateral buds was accelerated in Japanese pear [Pyrus pyrifolia (Burm.) Nak.] when vertical shoots were bent at a 45° angle in late June. The indole-3-acetic acid (IAA) concentration in lateral buds on vertical (control) shoots increased in mid-July, while remaining nearly constant in bent shoots. The abscisic acid (ABA) concentration of buds in bent shoots rose between 4 July and 15 Aug., whereas control shoots exhibited an increase in concentration followed by a decline. Gibberellin4+7 (GA4+7) concentration was high on 16 June, and then declined by 4 July, with the decline being greatest in bent shoots. Gibberellin4+7 concentration was higher in the buds on vertical shoots than in those on bent shoots for much of July. The concentrations of zeatin-type cytokinins (CKs) in lateral buds were higher in bent shoots than in vertical shoots. Bending of pear shoots may weaken competition between buds and other organs through altering hormone levels in lateral buds, resulting in acceleration of flower development.

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Akiko Watari, Toshio Hanada, Hisayo Yamane, Tomoya Esumi, Ryutaro Tao, Hideaki Yaegaki, Masami Yamaguchi, Kenji Beppu, and Ikuo Kataoka

Most commercial cultivars of japanese plum (Prunus salicina Lindl.) exhibit S-RNase-based gametophytic self-incompatibility (GSI), although some self-compatible (SC) cultivars exist. In this study, we characterized S-RNase and SFB, the pistil and pollen S determinants of the specificity of the GSI reaction, respectively, from four S-haplotypes, including a SC (Se) and three SI (Sa, Sb, and Sc) S-haplotypes of japanese plum. The genomic organization and structure of the SC Se-haplotype appear intact, because the relative transcriptional orientation of its S-RNase and SFB and their intergenetic distance are similar to those of the other three SI S-haplotypes of japanese plum and other Prunus L. species. Furthermore, there is no apparent defect in the DNA sequences of Se-RNase and SFBe. However, a series of transcriptional analyses, including real-time reverse transcriptase–polymerase chain reaction, showed that the Se-RNase transcript levels in the pistil are significantly lower than those of the Sa-, Sb-, and Sc-RNases, although transcripts of SFBa, SFBb, SFBc, and SFBe are present at similar levels in pollen. Furthermore, no Se-RNase spot was detected in two-dimensional polyacrylamide gel electrophoresis profiles of stylar extracts of the cultivars with the Se-haplotype. We discuss the possible molecular basis of SC observed with the Se-haplotype with special reference to the insufficient Se-RNase accumulation incited by the very low transcriptional level of Se-RNase in pistils.