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Indole-3-acetic Acid Sensitization of Phytochrome-Controlled Growth of Coleoptile Sections

James R. Shinkle and Winslow R. Briggs
Proceedings of the National Academy of Sciences of the United States of America
Vol. 81, No. 12, [Part 1: Biological Sciences] (Jun. 15, 1984), pp. 3742-3746
Stable URL: http://www.jstor.org/stable/24349
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Indole-3-acetic Acid Sensitization of Phytochrome-Controlled Growth of Coleoptile Sections
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Abstract

Addition of 6 μ M indole-3-acetic acid (IAA) to incubation buffer increases the sensitivity of coleoptile sections cut from dark-grown Avena sativa L. cv. Lodi to red light by a factor of 10,000, relative to the response in the absence of added IAA, without changing the maximum amount of light-induced growth. From 0.03 to 4 μ M IAA sections show at least a 100-fold increase in sensitivity to red light relative to the response in the absence of added IAA. In this IAA concentration range, the light-induced increase in elongation shows two phases of response to red-light fluence, which are separated by a plateau. The biphasic fluence--response curve is also characteristic of the red-light-induced stimulation of coleoptile growth in intact dark-grown seedlings. The effect of IAA on the sensitivity of the phytochrome-mediated growth response appears to be on some step in the transduction of the phytochrome signal, rather than on the growth response itself.

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