Changes of abscisic acid, indole-3-acetic acid and gibberellin-like substances in the flowers and developing fruitlets of citrus cultivar ‘Hyuganatsu’

Abstract

Endogenous hormonal changes associated with fruit set and growth were studied in ‘Hyuganatsu’ ( Citrus tamurana [Hort.] ex. Tanaka), a species which has no parthenocarpic ability. Concentrations and contents of abscisic acid (ABA), indole-3-acetic acid acid (IAA) and gibberillin (GA)-like substances were measured before, during and after anthesis, in several floral and fruitlet parts. On the day of anthesis, the ABA concentration in stamens had decreased to about 30% as compared to 5 days before, while the IAA concentration in stamens and petals had increased about twofold. Eight days after anthesis (DAA), the contents of ABA and IAA in the styles and in the fruitlets increased markedly, particularly in the pollinated flowers in which were found the highest values per fresh weight recorded in this study. The contents of GA-like substances rose continuously in the pollinated fruitlets, whereas in unpollinated ones no increase was found from 8 DAA. These changes in hormone levels are discussed in relation to the development of the floral parts and the early growth of the fruitlets.