Effect of 2,5‐norbornadiene on abscission and ethylene production in citrus leaf explants

Abstract

Citrus (Citrus sinensis L. Osbeck) leaf explants completely abscise within 48 h when exposed to saturating amounts of ethylene at 25°C. When 2,5‐norbornadiene was added, 2000 μl 1−1 reduced abscission of explants also exposed to 2 μl 1−1 of ethylene to the level of the control, and 8000 μl 1−1 reduced abscission in explants exposed to 10 μl 1−1 of ethylene to the level of the control, but abscission was complete when 1 000 μl 1−1 of ethylene was used in the presence of 8 000 μl 1−1 of 2,5‐norbornadiene. When explants were exposed to 2 μl 1−1 of ethylene, 2000 μl 1−1 of 2,5‐norbornadiene prevented abscission if applied up to 10 h after exposure to ethylene. After 18 h, applied 2,5‐norbornadiene had little effect on abscission at 48 h. A Lineweaver‐Burk plot gave a 1/2 maximum value of 0.12 μl 1−1 for ethylene on abscission, 2,5‐Norbornadiene gave competitive kinetics with respect to ethylene with a K1 value of approximately 120 μl 1−1 of 2,5‐norbornadiene. The presence of 2,5norbornadiene stimulated ethylene production, which progressively increased as the 2,5‐norbornadiene concentration was increased from 250 to 8 000 μl 1−1 2,5‐Norbornadiene also suppressed the induction of cellulase and polygalacturonase by ethylene. Together, 2,5‐norbornadiene and 2,4‐dichlorophenoxyacetic acid were more effective than either alone in reducing abscission. 2,5‐Norbornadiene also was effective in preventing the reduction of indole‐3‐acetic acid transport induced by ethylene.