Laboratory of Genetics and Program of Cellular and Molecular Biology, University of Wisconsin-Madison, 425G Henry Mall, Madison, Wisconsin 53706, USA.
Am J Bot. 2013 Jan;100(1):126-42. doi: 10.3732/ajb.1200318. Epub 2012 Oct 9.
During gravitropism, the potential energy of gravity is converted into a biochemical signal. How this transfer occurs remains one of the most exciting mysteries in plant cell biology. New experiments are filling in pieces of the puzzle. In this review, we introduce gravitropism and give an overview of what we know about gravity sensing in roots of vascular plants, with special highlight on recent papers. When plant roots are reoriented sideways, amyloplast resedimentation in the columella cells is a key initial step in gravity sensing. This process somehow leads to cytoplasmic alkalinization of these cells followed by relocalization of auxin efflux carriers (PINs). This changes auxin flow throughout the root, generating a lateral gradient of auxin across the cap that upon transmission to the elongation zone leads to differential cell elongation and gravibending. We will present the evidence for and against the following players having a role in transferring the signal from the amyloplast sedimentation into the auxin signaling cascade: mechanosensitive ion channels, actin, calcium ions, inositol trisphosphate, receptors/ligands, ARG1/ARL2, spermine, and the TOC complex. We also outline auxin transport and signaling during gravitropism.
在向地性中，重力势能被转化为生物化学信号。这种转化是如何发生的，仍然是植物细胞生物学中最令人兴奋的奥秘之一。新的实验正在填补这个谜题的各个部分。在这篇综述中，我们介绍了向地性，并概述了我们对维管植物根中重力感应的了解，特别强调了最近的论文。当植物根重新侧向定向时，柱细胞中淀粉体的再沉降是重力感应的关键初始步骤。这个过程以某种方式导致这些细胞的细胞质碱化，随后生长素外排载体（PINs）的再定位。这改变了整个根中的生长素流，在帽区产生生长素的侧向梯度，当信号传递到伸长区时，导致细胞的不同伸长和向重性弯曲。我们将提出以下因素在将信号从淀粉体沉降转移到生长素信号级联中的作用的证据：机械敏感离子通道、肌动蛋白、钙离子、肌醇三磷酸、受体/配体、ARG1/ARL2、亚精胺和 TOC 复合物。我们还概述了向地性过程中的生长素运输和信号转导。
