Masson Patrick H, Tasaka Masao, Morita Miyo T, Guan Changhui, Chen Rujin, Boonsirichai Kanokporn
Arabidopsis Book. 2002;1:e0043. doi: 10.1199/tab.0043. Epub 2002 Mar 27.
For most plants, shoots grow upward and roots grow downward. These growth patterns illustrate the ability for plant organs to guide their growth at a specified angle from the gravity vector (gravitropism). They allow shoots to grow upward toward light, where they can photosynthesize, and roots to grow downward into the soil, where they can anchor the plant as well as take up water and mineral ions.Gravitropism involves several steps organized in a specific response pathway. These include the perception of a gravistimulus (reorientation within the gravity field), the transduction of this mechanical stimulus into a physiological signal, the transmission of this signal from the site of sensing to the site of response, and a curvature-response which allows the organ tip to resume growth at a predefined set angle from the gravity vector.The primary sites for gravity sensing are located in the cap for roots, and in the endodermis for shoots. The curvature response occurs in the elongation zones for each organ. Upon gravistimulation, a gradient of auxin appears to be generated across the stimulated organ, and be transmitted to the site of response where it promotes a differential growth response. Therefore, while the gravity-induced auxin gradient has to be transmitted from the cap to the elongation zones in roots, there is no need for a longitudinal transport in shoots, as sites for gravity sensing and response overlap in this organ.A combination of molecular genetics, physiology, biochemistry and cell biology, coupled with the utilization of Arabidopsis thaliana as a model system, have recently allowed the identification of a number of molecules involved in the regulation of each phase of gravitropism in shoots and roots of higher plants. In this review, we attempt to summarize the results of these experiments, and we conclude by comparing the molecular and physiological mechanisms that underlie gravitropism in these organs.
GSPA: gravitational set point angle; IAA: indole-3-acetic acid; NAA: 1-naphthalene acetic acid; NPA: 1-N-naphthylphthalamic acid; 2,4-D: 2,4-dichlorphenoxy acetic acid; TIBA: 2,3,5-triiodobenzoic acid.
对于大多数植物来说，地上部分向上生长，地下部分向下生长。这些生长模式表明植物器官能够以与重力向量成特定角度的方式引导其生长（向地性）。它们使地上部分向上朝着光生长，在那里进行光合作用，使地下部分向下长入土壤，在那里固定植物并吸收水分和矿质离子。向地性涉及在特定反应途径中组织的几个步骤。这些步骤包括重力刺激的感知（在重力场中的重新定向）、将这种机械刺激转化为生理信号、将该信号从感知部位传递到反应部位，以及一种弯曲反应，使器官尖端能够从重力向量开始以预定的角度恢复生长。重力感知的主要部位在根的根冠以及地上部分的内皮层。弯曲反应发生在每个器官的伸长区。受到重力刺激后，生长素似乎会在受刺激的器官上形成梯度，并传递到反应部位，在那里促进差异生长反应。因此，虽然重力诱导的生长素梯度必须从根冠传递到根的伸长区，但地上部分不需要纵向运输，因为在这个器官中重力感知和反应的部位重叠。分子遗传学、生理学、生物化学和细胞生物学相结合，以及利用拟南芥作为模型系统，最近使得人们能够鉴定出一些参与高等植物地上部分和地下部分向地性各阶段调控的分子。在这篇综述中，我们试图总结这些实验的结果，并通过比较这些器官中向地性的分子和生理机制来得出结论。
GSPA：重力设定点角度；IAA：吲哚 - 3 - 乙酸；NAA：1 - 萘乙酸；NPA：1 - N - 萘基邻苯二甲酸；2,4 - D：2,4 - 二氯苯氧乙酸；TIBA：2,3,5 - 三碘苯甲酸
