Reduction in ethylene synthesis in parthenocarpic Actinidia deliciosa fruit induced by N-(2-chloro-4-pyridyl)-N′-phenylurea

Parthenocarpic kiwifruit Actinidia deliciosa was produced and induction of ethylene synthesis in response to ethylene treatment studied. At anthesis, flowers were treated with N -(2-chloro-4-pyridyl)- N ′-phenylurea (CPPU). CPPU-treated parthenocarpic fruit and pollinated normal fruit were harvested in early November, and then treated with 1000 μ l l −1 ethylene at 20°C for 24 h. Ethylene production following ethylene treatment was reduced and delayed in the parthenocarpic fruit. To investigate the mechanism of this reduction in ethylene synthesis, 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations, and gene expression of ACC synthase (using a cDNA probe, AD-ACS1) and of ACC oxidase (with a cDNA probe, AD-ACO1) were analyzed. ACC concentrations and levels in ACC synthase transcripts increased in the pollinated fruit 2 days after the 24 h ethylene treatment, but not in the parthenocarpic fruit. Accumulation of ACC oxidase transcripts was stimulated immediately by the 24 h ethylene treatment in both pollinated and parthenocarpic fruit. These results suggest that suppression of ethylene synthesis in parthenocarpic fruit resulted mainly from suppressed expression of ACC synthase.