Indolyl-3-acetic Acid and Ethylene Levels in Ripening Apple Fruits

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Abstract
Indolyl-3-acetic acid (IAA) levels in apple (Malus domestica Borkh.) fruits were determined fluorimetrically after formation of 2-methylindolo-α-pyrone in purified extracts. The properties of the fluorescent products in apple samples were identical with those of authentic IAA. The assays were performed on samples of cortex with or without peel from the varieties James Grieve and Worcester Pearmain during the last 50—70 d of their development on the tree. At the same time the ethylene concentration in the core cavity of the fruits was measured as a guide to the progress of ripening. IAA concentration showed a 3—4-fold increase prior to the rapid rise in ethylene concentration but fell to about its original level as this rise occurred. IAA was also measured in the seeds of James Grieve apples, where it rose to a peak concentration and declined before the peak observed in the fleshy tissue of the fruit. IAA in the seeds increased markedly after 15 d storage of the fruit harvested 136 d after full bloom.