Indole-3-acetic acid sensitization of phytochrome-controlled growth of coleoptile sections.
Addition of 6 muM 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 muM 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.
Department of Plant Biology, Carnegie Institution of Washington, 290 Panama Street, Stanford, CA 94305.
J R
JR
Shinkle
W R
WR
Briggs