Physiology of Olive Leaf Abscission Induced by Phosphorus

Adding Al 2 O 3 to 8-hydroxyquinoline citrate (8-HQC) solution did not alter the sensitivity of the leaf abscission zone to external ethylene. Exogenous ethylene at 791 nl·liter -1 for 72 to 120 hours and at 193 nl·liter -1 for 120 hours induced leaf abscission, whereas no leaf abscission occurred at 47 nl·liter -1 for 72 to 120 hours. Ethylene at 791 nl·liter -1 for 72 to 120 hours increased ethylene evolution, but the amount of ethylene evolved from the explants does not seem to be enough to induce leaf abscission. Three different ethylene inhibitors—aminooxyacetic acid (AOA), CoCl 2 , and aminoethoxyvinylglycine (AVG)—were used to determine whether P-induced leaf abscission was mediated through elevated ethylene evolution. Although AOA and CoCl 2 failed to inhibit ethylene evolution from the explants stem-fed with NaH 2 PO 4 , AVG inhibited ethylene evolution. Each inhibitor, except 5 m m CoCl 2 , promoted leaf abscission when administered alone or with P. Our results reveal that P-induced olive leaf abscission may occur without elevated ethylene evolution. At 40 or 75 m m NaH 2 PO 4 , abscission did not occur until explants were removed from N 2 and placed in ambient air.