Distribution of Endogenous Indole-3-acetic Acid and Growth Inhibitor(s) in Phototropically Responding Oat Coleoptiles

摘要

The relationship between the flank growth of oat (Avena sativaL. cv. Victory) coleoptiles and the distribution of endogenous indole-3-acetic acid (IAA) and growth inhibitor(s) in the coleoptiles was studied for the second positive phototropic curvature induced by a continuous unilateral illumination with white light (0.1 W.m−2). The phototropic curvature was caused by growth inhibition at the lighted side and growth promotion at the shaded side. Using electron capture detection gas chromatography, we analyzed the distribution of endogenous IAA in phototropically responding oat coleoptiles and found that the IAA was evenly distributed over the lighted and shaded sides during the phototropic response; there was also no detectable difference in the amounts of IAA between phototropically stimulated and non-irradiated coleoptiles. By contrast, oat coleoptile straight-growth test results showed that the amount of unknown acidic growth inhibitor(s), different from abscisic acid, increased in the lighted half of the coleoptiles and decreased in the shaded half, as compared to the amount in the non-irradiated half. These data suggest that the phototropic curvature of oat coleoptile is induced by a difference in lateral flank growth through a lateral gradient of endogenous growth inhibitor(s) rather than of IA