An increase in citrus fruit (Kiyomi tangor) abscission induced by ABA is accompanied by an IAA increase in the abscission zone and ethylene production

SummaryChange in IAA concentrations in the peduncle, branch and intervening abscission zone were measured to clarify the involvement of IAA in citrus fruit drop in response to ABA application. Results indicating the importance of an IAA increase in the abscission zone were obtained. One day after application of ABA, the concentration of IAA in the abscission zone showed a temporary increase and then a decrease. The concentration of IAA in the abscission zone was dependent on the concentration of ABA applied. Changes in the production of ethylene, which is involved in the process of abscission and which is induced by IAA, in explants from treated leafy inflorescences, were examined. The fruit-abscission ratios were also investigated in relation to the time required for preparation. Explants sampled 0±1.d after application showed little abscission or ethylene production during the first 24 h incubation. During the next 24 h, almost all the ABA-applied explants abscinded, as did the control, but the former p...