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Articles

The Promotion of Indole-3-acetic Acid Oxidation in Pea Buds by Gibberellic Acid and Treatment ¹

^a Department of Biology, Hope College, Holland, Michigan 49423

Terminal buds of dark-grown pea (Pisum sativum) seedlings have an indole-3-acetic acid oxidase which does not require Mn²⁺ and 2,4-dichlorophenol as cofactors. Oxidase activity is at least 50 times higher in buds of tall peas than in dwarf seedlings. Administration of gibberellic acid to dwarf peas stimulates both growth and indoleacetic acid oxidase activity to the same levels as in tall seedlings. By contrast, indoleacetic acid oxidation assayed in the presence of Mn²⁺ and 2,4-dichlorophenol proceeds at similar rates regardless of gibberellin application. Treatment of tall peas with the growth retardant AMO-1618 reduces growth and oxidase activity. Such treated seedlings are indistinguishably dwarf. The enzyme does not appear to be polyphenol oxidase, nor do the results suggest that reduced activity in dwarf buds is due to higher levels of a dialyzable inhibitor. The peroxidative nature of the oxidase is probable.

¹ This investigation was supported by Grant GB-8729 to R.O. from the National Science Foundation. J.W. was supported by Undergraduate Research Participation Grant GY-4276 from the National Science Foundation.