Effects of Iron and Copper Ions in Promotion of Selective Abscission and Ethylene Production by Citrus Fruit and the Inactivation of Indoleacetic Acid

Application of Cu(2+) (<10(-2) M) and Fe(3+) ions as aqueous solutions of chloride salts promoted fruit abscission, erratic rind damage, and ethylene production of various citrus species with little to no defoliation. Mixing of 10(-5) M Cu(2+) or Fe(3+) ions with equimolar indole-3-acetic acid resulted in a reduction of the ultraviolet absorption at 220 nanometers, and an increase at 245 nanometers. Ultraviolet irradiation accelerated the change by Fe(3+) and Cu(2+) ions in the absorption of indole-3-acetic acid. Pretreatment of indole-3-acetic acid with Fe(3+) and Cu(2+) ions for 6 hours resulted in more than 90% reduction in its growth-promoting activity in the Avena bioassay, even when cations were removed by chromatography. Acceleration of abscission by Fe(3+) and Cu(2+) ions could be related to both promotion of ethylene production and direct inactivation of auxin.