Kiss John Z, Mullen Jack L, Correll Melanie J, Hangarter Roger P
Department of Botany, Miami University, Oxford, Ohio 45056, USA.
Plant Physiol. 2003 Mar;131(3):1411-7. doi: 10.1104/pp.013847.
The interaction of tropisms is important in determining the final growth form of the plant body. In roots, gravitropism is the predominant tropistic response, but phototropism also plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism that is mediated by the phototropin family of photoreceptors. In contrast, red light induces a positive phototropism in Arabidopsis roots. Because this red-light-induced response is weak relative to both gravitropism and negative phototropism, we used a novel device to study phototropism without the complications of a counteracting gravitational stimulus. This device is based on a computer-controlled system using real-time image analysis of root growth and a feedback-regulated rotatable stage. Our data show that this system is useful to study root phototropism in response to red light, because in wild-type roots, the maximal curvature detected with this apparatus is 30 degrees to 40 degrees, compared with 5 degrees to 10 degrees without the feedback system. In positive root phototropism, sensing of red light occurs in the root itself and is not dependent on shoot-derived signals resulting from light perception. Phytochrome (Phy)A and phyB were severely impaired in red-light-induced phototropism, whereas the phyD and phyE mutants were normal in this response. Thus, PHYA and PHYB play a key role in mediating red-light-dependent positive phototropism in roots. Although phytochrome has been shown to mediate phototropism in some lower plant groups, this is one of the few reports indicating a phytochrome-dependent phototropism in flowering plants.
向性的相互作用对于确定植物体的最终生长形态很重要。在根中，向重力性是主要的向性反应，但在开花植物中，向光性也在根的定向生长中发挥作用。在蓝光或白光下，根表现出由向光素家族光感受器介导的负向光性。相比之下，红光诱导拟南芥根产生正向光性。由于这种红光诱导的反应相对于向重力性和负向光性都较弱，我们使用了一种新型装置来研究向光性，避免了抵消重力刺激带来的复杂性。该装置基于一个计算机控制系统，利用对根生长的实时图像分析和反馈调节的旋转台。我们的数据表明，该系统对于研究根对红光的向光性很有用，因为在野生型根中，使用该装置检测到的最大曲率为30度至40度，而没有反馈系统时为5度至10度。在正向根向光性中，对红光的感知发生在根本身，不依赖于由光感知产生的来自地上部分的信号。光敏色素（Phy）A和phyB在红光诱导的向光性中严重受损，而phyD和phyE突变体在这种反应中正常。因此，PHYA和PHYB在介导根中依赖红光的正向光性中起关键作用。尽管已表明光敏色素在一些低等植物类群中介导向光性，但这是少数表明开花植物中存在依赖光敏色素的向光性的报告之一。
