Far red light control of elongation in light-grown bean hypocotyl: Effect on different age zones and interaction with indole-3-acetic acid

The effect of far red light on the light-grown bean hypocotyland its interaction with indole-3-acetic acid (IAA) were studied.Elongation of younger zones of the hypocotyl was inhibited butthat of older zones was promoted by far red light. This wascontrolled by phytochrome. Both the hook and shank portionscould receive far red light and its effect could be transmittedto either portions of the hypocotyl. When IAA was applied to the upper cut surface of the hypocotylunit, elongation of the shank portion was promoted even withoutfar red irradiation. IAA did not change the aspect of the growthcurves but amplified the elongation of each zone. When IAA wasapplied to each zone of the shank portion, elongation of zonesolder than the treated one was promoted but that of youngerzones was inhibited. This effect was emphasized by far red light.When IAA was applied to the older shank portion, elongationof the treated zone was synergistically promoted by IAA andfar red light, but when applied to the elbow or younger shankportion, far red light completely nullified the promoting effectof IAA. (Received October 1, 1979; )