Anatomical and histochemical studies of maturation and the accumulation of polysaccharides or volatile organic compounds in Japanese wild cherry fruit following ethephon application

Abstract

The leaf of the Japanese wild cherry, Prunus Sato-zakura Group, especially ‘Oshima-zakura’, releases volatile organic compounds (VOCs) such as polysaccharides or coumarin from the leaves or fruits. These substances have a pleasant smell and exert a bactericidal effect. However, little information is available on the maturation and development of fragrant ingredients in ‘Oshima-zakura’ fruit. In this study, we used histochemistry to observe polysaccharide or VOC release from the fruit tissue. Ethephon (500 ppm) was sprayed on immature green fruit. Fruit samples were obtained at the immature (green), turning (red), and matured (black) stages. Fruit ripening proceeded about 3 to 5 days after ethephon application. The surface cells of the fruit epicarp were composed of a thick cuticle with wax, and two to three layers of cells were found underneath the cuticle, which contained chloroplast during the immature stage. As the fruit matured, these cells developed vacuoles in the epicarp tissue and anthocyanin accumulated significantly following ethephon application. When stained with toluidine blue-O, cells of the fruit mesocarp tissue exhibited a red-purplish colour following treatment with ethephon. This indicated that cells of the mesocarp contained polysaccharide, such as pectic substances or VOCs, especially coumarin. Accordingly, the substances that stained red-purplish may be antifungal and may exhibit antifeedant properties against pests. We conclude that polysaccharides or VOCs, especially coumarin, may increase the functional potential of wild cherry in addition to its fragrant properties, following treatment with ethephon.