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Articles

Azido Auxins ¹

Photolysis in Solution and Covalent Binding to Soybean

School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, Department of Plant Biology, University of Illinois, Urbana, Illinois 61801

The potential of three auxin analogs, 4-, 5-, and 6-azidoindole-3-acetic (4-N₃IAA, 5-N₃IAA, and 6-N₃IAA), as photoaffinity labeling agents for the detection and isolation of auxin receptors was assessed by irradiating these compounds at 365 nm on TLC plates, in solution, and in contact with soybean (Glycine max L. Merr. var. Wayne) hypocotyl. Photolysis on TLC plates produces immobile spots, indicating extremely polar or covalent binding of the photoproducts to the plates. On irradiation in buffer or in buffer containing sucrose, all three compounds decompose at rates that are first order in N₃IAA to give fluorescent solutions. Photolysis through a Pyrex filter is slower than that through quartz, but the filter prevents tissue damage and allows a given dose of irradiation to photolyze all three N₃IAAs to the same extent. The effects of photolysis of these compounds in vivo were evaluated with a straight growth assay using etiolated soybean hypocotyl segments. According to this assay, the photoproducts of the N₃IAAs possess little auxin activity. Irradiation of soybean hypocotyl tissue after 1-hour exposure to 4-N₃IAA in the dark causes the tissue to grow during 12 hours as much as tissue that is continuously exposed to 4-N₃IAA in the dark for this period, suggesting that, on photolysis, this auxin analog binds irreversibly to an auxinsensitive site. Although the fluorescence intensity of the photolyzed N₃IAAs is weak enough to require another method of detecting the bound analog under physiological conditions, the evidence for covalent binding of the N₃IAAs on photolysis implies that these compounds will be satisfactory photoaffinity labeling agents.

³ Department of Plant Biology.

¹ Supported by grants from the National Science Foundation (PCM 77-14175, PCM 80-21632, PCM 82-40868, CHE 76-22001, and CHE 81-21796). Presented, in part, at the Annual Meeting of the American Society of Plant Physiologists, Champaign-Urbana, IL, June 13-17, 1982.