Analyses and application of self-incompatibility gene products in the Japanese pear

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In pollen tubes treated with S-RNase in vitro, phosphoenolpyruvate carboxylase (PEPC) and isocitrate dehydrogenase (ICDH) activities showed little reduction, but invertase (INV) and glutaraldehyde 3-phosphate dehydrogenase (GPD) were strongly inactivated. PEPC and ICDH may be present as a protein form in a pollen grain, whereas INV and GPD may be newly synthesized during pollen-tube development. The enzymes involved in energy metabolism such as INV and GPD may be targets of S-RNase.Cultivar difference in S4-RNase distribution in the style was investigated using the S4-RNase atiserum. 'Kosui' contained higher S4-RNase in upper and middle part of the style, but 'Nijisseiki' did in middle part. The S4-RNase was clearly detected immunologically in 'Osa-Nijisseiki' style and almost all the RNase contained in upper style of the cultivar.S-RNase gene expression was cultivar dependent; lower expression of S2-RNase was observed in 'Gold-Niisseiki' and 'Osa-Nijisseiki'. S4-RNase expression was lower in 'Kosui', 'Osa-Nijisseiki', and so on. Clear relationships, however, were not observed between the gene expression and S-RNase content.S2-RNase gene expression declined by 20% of control (the day of anthesis) two days after pollination; pollination type (cross-, self-, or non-pollination) seemed not to affect the expression level. However, the level one day after pollination showed following order; cross>non>self. The style may recognize its mate and regulate S-RNase expression during early stages of pollen-tube elongation.Fruit set was 19.4% following self-pollination in weakly self-incompatible 'Okusankichi', whereas no fruit was obtained in strongly self-incompatible 'Hakko'. Several individuals among the F1 progenies between both cultivars showed a self fruitful character, indicating that weak incompatibility of 'Okusankichi' is heritable. Thus, breeding of self-thinning cultivar will be successful in the near future.