Changes in cytokinin content during early fruit development in two persimmon cultivars, ‘Izu’ and ‘Saefuji’

Persimmon exhibits three distinct stages of fruit growth, in which a slow-growth stage separates two rapid-growth stages. The first stage is associated with rapid cell division, influenced by cytokinin. We analyzed the cytokinin contents during early fruit development in two cultivars (‘Izu’ and ‘Saefuji’) contrasting fruit shapes. The fruit shape of ‘Izu’ was characterized as a flatter round shape, while that of ‘Saefuji’ was long-sharper. The cytokinin content was measured by C18-HPLC separation and ELISA with anti t-zeatin riboside (t-ZR) and anti-isopentenyladenosine (iPA) antiserum. The existence of t-zeatin (t-Z), t-ZR was confirmed by GC-MS analysis. The highest immunoreactivity was detected in the fractions of t-Z glucosides. The active t-Z was metabolized to inactivated glucoside form at early fruit development. Each active cytokinin content in both cultivars was highest during the pre-bloom period and decreased rapidly during post-bloom. The order of each active cytokinin level, from the highest to the lowest, was t-ZR > t-Z>>iP > iPA. The t-Z and t-ZR content of ‘Izu’ was higher than ‘Saefuji’ during the pre-bloom period. We investigated the effect of synthetic cytokinins on fruit development and revealed that pre-bloom treatment produced a flatter shape of fruit in persimmon (Itai et al., 1995). Our result suggested that a higher level of t-Z and t-ZR might promote transverse growth in ‘Izu’, the cultivar of flatter shape.