Timing Abscission in Phaseolus Vulgaris L. By Controlling Ethylene Production and Sensitivity to Ethylene

SUMMARY Abscission in explants excised from the primary‐leaf petioles of dwarf bean (Phaseolus vulgaris L. cv. Canadian Wonder) is accelerated by removing the leaf‐blade 24 or 48 hours before the explants are cut. Deblading increases ethylene production before weakening of the abscission zone begins and the amount of ethylene produced is sufficient to promote abscission. Deblading also enhances the responsiveness of explants to ethylene and it is proposed that these two effects of deblading together account for the subsequent acceleration of abscission. If the auxin indol‐3‐yl acetic acid is applied to freshly debladed petiole stumps the responses to deblading do not occur. Explants from older plants abscind more slowly than those from younger plants and the difference can be related to the higher sensitivity to ethylene of younger explants, rather than to differences in their patterns of ethylene production. The nature of this sensitivity is briefly discussed.