Effect of silver ions and ethylene on auxin metabolism and auxininduced ethylene production in tobacco leaf discs

The antagonistic effects of ethylene and Ag + on the metabolism of [1‐ 14 C]indole‐3‐acetic acid (IAA) and on the rates of ethylene production were studied in tobacco leaf discs ( Nicotiana rustica var. Brasilia ). During the first 10 h of incubation, Ag + ‐pretreated leaf discs contained more free [ 14 C]IAA than untreated ones due to decreased oxidative decarboxylation, and the discs also produced more ethylene. Exogenously supplied ethylene nullified these effects of Ag + . However, the most pronounced effect of Ag + in increasing ethylene production, as well as the strongest antagonistic effect of exogenous ethylene, were found between 24 and 48 h of incubation. During this time span no effect on the level of free IAA and on its decarboxylation could be observed. It is suggested that ethylene exerted its autoinhibitory effect by a feedback control on the IAA‐induced ethylene biosynthesis. Possible mechanisms for the autoinhibitory effect of ethylene are discussed.