Mullen Jack L, Weinig Cynthia, Hangarter Roger P
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Plant Cell Environ. 2006 Jun;29(6):1099-106. doi: 10.1111/j.1365-3040.2005.01484.x.
As a rosette plant, Arabidopsis thaliana forms leaves near to the ground, which causes the plant to be vulnerable to shading by neighbours. One mechanism to avoid such shading is the regulation of leaf inclination, such that leaves can be raised to more vertical orientations to prevent neighbouring leaves from overtopping them. Throughout Arabidopsis rosette development, rosette leaves move to more vertical orientations when shaded by neighbouring leaves, exposed to low light levels or placed in the dark. After dark-induced reorientation of leaves, returning them to white light causes the leaves to reorient to more horizontal inclinations. These light-dependent leaf movements are more robust than, and distinct from, the diurnal movements of rosette leaves. However, the movements are gated by the circadian clock. The light-dependent leaf orientation response is mediated primarily through phytochromes A, B and E, with the orientation varying with the ratio of red light to far-red light, consistent with other shade-avoidance responses. However, even plants lacking these phytochromes were able to alter leaf inclination in response to white light, suggesting a role for other photoreceptors. In particular, we found significant changes in leaf inclination for plants exposed to green light. This green light response may be caused, in part, by light-dependent regulation of abscisic acid (ABA) biosynthesis.
作为一种莲座状植物，拟南芥在靠近地面的位置形成叶片，这使得植株容易受到相邻植株遮荫的影响。避免这种遮荫的一种机制是调节叶片倾角，使叶片能够向上提升至更垂直的方向，以防止相邻叶片遮挡它们。在拟南芥莲座叶发育的整个过程中，当受到相邻叶片遮荫、处于低光照水平或置于黑暗环境中时，莲座叶会向更垂直的方向移动。在黑暗诱导叶片重新定向后，将它们重新置于白光下会使叶片重新定向至更水平的倾角。这些依赖光的叶片运动比莲座叶的昼夜运动更强烈，且与之不同。然而，这些运动受生物钟的调控。依赖光的叶片定向反应主要通过光敏色素A、B和E介导，其定向随红光与远红光的比例而变化，这与其他避荫反应一致。然而，即使是缺乏这些光敏色素的植株也能够响应白光改变叶片倾角，这表明其他光感受器也发挥了作用。特别是，我们发现暴露于绿光下的植株叶片倾角有显著变化。这种绿光反应可能部分是由脱落酸（ABA）生物合成的光依赖性调节引起的。
