Effect of calcium, (2-chloroethyl) phosphonic acid and ethylene on bean leaf abscission.

The effects of CaCl2, (2-chloroethyl) phosphonic acid (Ethephon) and ethylene on leaf abscission of debladed and intact bean plants (Phaseolus vulgaris L.) were studied. Ethephon (1000 μg/l) and ethylene (8 μl/l) induced abscission in debladed and intact plants in 24-72 h whereas IAA (10(-5)M), cycloheximide (10(-5)M) and CaCl2 (0.068M) delayed abscission in debladed plants. CaCl2 completely inhibited the abscission-enhancing effect of Ethephon in intact bean leaves. When CaCl2 and Ethephon were applied simultaneously to separate halves of the leaf blade, leaves with Ethephon applied closest to the pulvinus abscised rapidly; when CaCl2 was applied closest to the pulvinus, abscission was prevented. Calcium pre-treatment prior to ethylene (8 μl/l) treatment of debladed plants delayed abscission as compared to those treated with ethylene alone.