Effects of GA3 and Ethephon on the Level of ABA and Peroxidase Activity in the Peel of Satsuma Mandarin (Citrus unshiu Marc.)

GA3 and ethephon were applied to satsuma mandarin (Citrus unshiu Marc.) fruit at a concentration of 100ppm 35 days before harvest. GA3 depressed the level of ABA in the flavedo during fruit maturation and senescence. On the contrary, ethephon raised the ABA level. Peroxidase activity in the flavedo decreased rapidly during fruit maturation and then leveled off towards senescence. This rapid decrease in enzyme activity was inhibited by GA3 application and accelerated by ethephon. Although there were 15 isozymes of peroxidase in the flavedo of immature fruit, some of the isozymes disappeared during fruit maturation and only 9 isozymes were finally found at harvest time. GA3 application decreased the reduction in number of peroxidase isozymes though it conversely increased the reduction in some isozymes. The activity of 2 isozymes was increased and other 2 isozymes disappeared by ethephon treatment. In general, very low activity and fewer isozymes of peroxidase were observed in the albedo as compared to those in the flavedo.