Calcium distribution in the abscission zone of bean leaves: electron microprobe x-ray analysis.

The calcium content and distribution across the abscission zones of (2-chloroethyl) phosphonic acid-treated bean (Phaseolus vulgaris L. var. Contender) leaves were lower and not uniformly distributed as compared to the control. Calcium chloride-treated bean leaves had a higher calcium content, with more calcium localized in the potential abscission layer. Ethephon treatment promoted abscission in both debladed and nondebladed plants; there was a corresponding decrease in calcium in the abscission zone just prior to separation. Deblading of bean leaves under a calcium solution increased the calcium level in the abscission zone and delayed abscission.