Kuhn H, Galston A W
Department of Biology, Yale University, New Haven, CT 06511-8112, USA.
Photochem Photobiol. 1992;55(2):313-8. doi: 10.1111/j.1751-1097.1992.tb04243.x.
Etiolated pea seedlings require transformation of Pr phytochrome to Pfr before they display optimal phototropic response to unilateral blue light. This study investigates the possible role of auxin transport in explaining these phenomena. Labeled [2-14C]IAA applied to the intact terminal buds of dark-grown and red light-treated pea seedlings was measured 210 min later on the shaded and illuminated sides of the epicotyl as a function of direction and duration of irradiation with blue light. Totally darkened epicotyls show an asymmetry in distribution of radioactivity in the upper growth zone of the epicotyl, in favor of the side under the concave part of the apical hook. Red light, which greatly potentiates curvature toward subsequent unilateral blue light, lowers this asymmetry. Blue light directed to the epicotyl of red-pretreated plants in a plane parallel to the hook and from the side bearing the convex portion of the hook induces positive phototropic curvature as well as a surplus of radioactivity on the illuminated side of the upper epicotyl and on the shaded side of the lower growth zone of the epicotyl. Light directed to the side bearing the concave part of the hook also causes an accumulation of counts in the upper part of the lighted side but produces neither curvature of the epicotyl nor accumulation of counts in the lower shaded side. Because of this built-in physiological asymmetry in the growth zone just below the apical hook, it is difficult to explain the effects of red and blue light on curvature in terms of patterns of auxin distribution alone.
黄化豌豆幼苗在对单侧蓝光表现出最佳向光性反应之前，需要将红光光敏色素转化为远红光光敏色素。本研究调查了生长素运输在解释这些现象中可能发挥的作用。将标记的[2-¹⁴C]吲哚乙酸应用于黑暗生长和红光处理的豌豆幼苗的完整顶芽，210分钟后，测量上胚轴遮光侧和受光侧的放射性，作为蓝光照射方向和持续时间的函数。完全黑暗的上胚轴在上胚轴上部生长区的放射性分布存在不对称，有利于顶钩凹面下方的一侧。红光极大地增强了对随后单侧蓝光的弯曲，降低了这种不对称性。在与顶钩平行的平面上，从顶钩凸面一侧照射经红光预处理植物的上胚轴的蓝光，会诱导正向光性弯曲，以及上胚轴上部受光侧和上胚轴下部生长区遮光侧的放射性过剩。照射到顶钩凹面一侧的光也会导致受光侧上部的计数积累，但既不会引起上胚轴弯曲，也不会导致下部遮光侧的计数积累。由于顶钩下方生长区存在这种内在的生理不对称性，仅根据生长素分布模式很难解释红光和蓝光对弯曲的影响。
