Antagonistic changes between abscisic acid and gibberellins in citrus fruits subjected to a series of different water conditions

Abstract

The relationship between absicisic acid (ABA) and gibberellin (GA) changes in developing fruitlets from both Clementina (Citrus clementina, Hort ex Tan) and Okitsu (Citrus unshiu, (Mak) Marc.) trees subjected to changing water conditions was investigated. The treatments consisted of a series of water stress, rainfall, and re-irrigation periods. To confirm the effectiveness of the imposed water changes, leaf water potential and soil moisture were measured. The data indicated that there were antagonistic changes between ABA and GA(20), because in both species ABA increased and GA(20) decreased during water stress, whereas re-hydration via either rainfall or irrigation reduced ABA but increased GA20. In addition, the data indicated that during water stress GA1 also decreased, whereas GA(8) did not change. After re-hydration, however, levels of GA(20) products, in general were rather dependent upon the hormonal levels induced in the previous water status. In conclusion, the results showed the occurrence of antagonistic changes between the levels of ABA and GA(20) in developing citrus fruitlets subjected to changing water conditions. The data might suggest that gibberellin 20-oxidase is regulated by water stress in citrus fruits.