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Nitric oxide mediates gravitropic bending in soybean roots

Tang, Zhangcheng; Neill, Steven J.; Cai, Weiming; Hu, Xiangyang


Zhangcheng Tang

Steven J. Neill

Weiming Cai

Xiangyang Hu


Plant roots are gravitropic, detecting and responding to changes in orientation via differential growth that results in bending and reestablishment of downward growth. Recent data support the basics of the Cholodny-Went hypothesis, indicating that differential growth is due to redistribution of auxin to the lower sides of gravistimulated roots, but little is known regarding the molecular details of such effects. Here, we investigate auxin and gravity signal transduction by demonstrating that the endogenous signaling molecules nitric oxide (NO) and cGMP mediate responses to gravistimulation in primary roots of soybean (Glycine max). Horizontal orientation of soybean roots caused the accumulation of both NO and cGMP in the primary root tip. Fluorescence confocal microcopy revealed that the accumulation of NO was asymmetric, with NO concentrating in the lower side of the root. Removal of NO with an NO scavenger or inhibition of NO synthesis via NO synthase inhibitors or an inhibitor of nitrate reductase reduced both NO accumulation and gravitropic bending, indicating that NO synthesis was required for the gravitropic responses and that both NO synthase and nitrate reductase may contribute to the synthesis of the NO required. Auxin induced NO accumulation in root protoplasts and asymmetric NO accumulation in root tips. Gravistimulation, NO, and auxin also induced the accumulation of cGMP, a response inhibited by removal of NO or by inhibitors of guanylyl cyclase, compounds that also reduced gravitropic bending. Asymmetric NO accumulation and gravitropic bending were both inhibited by an auxin transport inhibitor, and the inhibition of bending was overcome by treatment with NO or 8-bromo-cGMP, a cell-permeable analog of cGMP. These data indicate that auxin-induced NO and cGMP mediate gravitropic curvature in soybean roots. © 2005 American Society of Plant Biologists.


Cai, W., Neill, S. J., Tang, Z., & Hu, X. (2005). Nitric oxide mediates gravitropic bending in soybean roots. Plant Physiology, 137(2), 663-670.

Journal Article Type Article
Publication Date Dec 1, 2005
Journal Plant Physiology
Print ISSN 0032-0889
Publisher American Society of Plant Biologists
Peer Reviewed Peer Reviewed
Volume 137
Issue 2
Pages 663-670
Keywords nitric oxide, gravitropic bending, soybean roots
Public URL
Publisher URL
Additional Information Additional Information : This paper results from a collaborative BBSRC and Royal Society funded project between UWE and SIPPE, Shanghai, China. Neill conceived the experiments and wrote the paper.

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