Université Clermont Auvergne, INRA, PIAF, Clermont-Ferrand, France.
Aix Marseille University, CNRS, IUSTI, Marseille, France.
J Exp Bot. 2019 Mar 27;70(6):1955-1967. doi: 10.1093/jxb/erz027.
Gravity is a major abiotic cue for plant growth. However, little is known about the responses of plants to various patterns of gravi-stimulation, with apparent contradictions being observed between the dose-like responses recorded under transient stimuli in microgravity environments and the responses under steady-state inclinations recorded on earth. Of particular importance is how the gravitropic response of an organ is affected by the temporal dynamics of downstream processes in the signalling pathway, such as statolith motion in statocytes or the redistribution of auxin transporters. Here, we used a combination of experiments on the whole-plant scale and live-cell imaging techniques on wheat coleoptiles in centrifuge devices to investigate both the kinematics of shoot-bending induced by transient inclination, and the motion of the statoliths in response to cell inclination. Unlike previous observations in microgravity, the response of shoots to transient inclinations appears to be independent of the level of gravity, with a response time much longer than the duration of statolith sedimentation. This reveals the existence of a memory process in the gravitropic signalling pathway, independent of statolith dynamics. By combining this memory process with statolith motion, a mathematical model is built that unifies the different laws found in the literature and that predicts the early bending response of shoots to arbitrary gravi-stimulations.
重力是植物生长的主要非生物线索。然而，人们对植物对各种重刺激模式的反应知之甚少，在微重力环境下瞬态刺激下记录的剂量样反应与在地球上记录的稳态倾斜下的反应之间存在明显的矛盾。特别重要的是，器官的向重力性反应如何受到信号通路中下游过程的时间动态的影响，例如质体中的平衡石运动或生长素转运体的再分配。在这里，我们使用组合实验在整个植物尺度和活体细胞成像技术在小麦胚芽鞘在离心设备来研究shoot-bending 的运动学诱导瞬态倾斜，和质体在响应细胞倾斜。与微重力下的先前观察结果不同，shoots 对瞬态倾斜的反应似乎与重力水平无关，其响应时间远长于质体沉降的持续时间。这揭示了向重力信号通路中存在记忆过程，而不依赖于质体动力学。通过将这个记忆过程与质体运动相结合，建立了一个数学模型，该模型统一了文献中发现的不同规律，并预测了 shoots 对任意重刺激的早期弯曲反应。
