Azido Auxins

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Abstract
The potential of 3 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 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 3 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 N3IAA 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 N3IAA possess litle auxin activity. Irradiation of soybean hypocotyl tissue after 1-h exposure to 4-N3IAA in the dark causes the tissue to grow during 12 h 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 auxin-sensitive site. Although the fluorescence intensity of the photolyzed N3IAA is weak enough to require another method of detecting the bound analog under physiological conditions, the evidence for covalent binding of the N3IAA on photolysis implies that these compounds will be satisfactory photoaffinity labeling agents.