Effects of light on auxin-induced elongation of light-grown cucumber hypocotyl sections

The effect of light on IAA-induced elongation of light-grown cucumber hypocotyl sections was examined. There was no difference in the optimal concentration of IAA between light and darkness and the biphasic pattern of IAA-induced elongation also was obtained in both states. Elongation of the first phase was not affected by light, but that of the second phase was influenced by the light condition of the first phase; dark incubation for the first 3 hr resulted in a larger IAA-induced elongation in the second phase. For the maximum IAA-induced elongation, at least 3 hr of light exposure in the second phase was necessary. Simultaneously applied photosynthetic inhibitors, DCMU, CMU and o-phenanthroline, synergistically enhanced IAA-induced elongation in light, but not in the dark. They were not effective when IAA treatment preceded the treatment with them.