Changes of endogenous levels of ABA, IAA and GA-like substances in fruitlets of parthenocarpic persimmon

The reproductive organ of parthenocarpic persimmon (Diospyros kaki Thunb. ' Hiratanenashi') was sampled from -5 to 122 days after flowering (DAF). The endogenous levels of abscisic acid (ABA) and indole- 3-acetic acid (IAA) we re analyzed by gas chromatograph-mass spectrometry (GC-MS), and those of gi bberellin (GA)-like substances were determined by the dwarf rice bioassay. Fruitlet abscission occurred mainly from 13 to 62 DAF and peaked at 41 DAF. A relatively rapid increase of fresh weight of fruitlets occurred until 41 DAF; thereafter, the growth rate was moderate. The weight of the calyx inc reased until 13 DAF. The ABA concentrations in fruitlets was higher from fl owering to 28 DAF than the remainder period. The calyx at 13 DAF had the ma ximum ABA concentration of all parts analyzed. IAA in the ovary/fruitlet in creased about Is times in content and 5 times in concentration from -5 to 0 DAF, and decreased to less than half in content by 13 DAF. The concentrati on of GA-like substances in fruitlets at flowering was also high, and incre ased at 41 and 122 DAF. At 5 days before flowering, the calyx had a higher concentration and content of three phytohormones than the ovary. These resu lts suggest that the genetical increases of IAA and GA-like substances in t he fruitlet of the parthenocarpic persimmon during flowering may result in continued growth, but the interaction between increased ABA and decreased I AA and GA-like substances in the fruitlet before fruitlet-drop may induce i ts abscission.