Mechanoreceptors rather than sedimentable amyloplasts perceive the gravity signal in hypergravity-induced inhibition of root growth in azuki bean
Kouichi Soga A C , Kazuyuki Wakabayashi A , Seiichiro Kamisaka B and Takayuki Hoson AA Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
B Department of Biology, Faculty of Science, Toyama University, Gofuku, Toyama 930-8555, Japan.
C Corresponding author. Email: soga@sci.osaka-cu.ac.jp
Functional Plant Biology 32(2) 175-179 https://doi.org/10.1071/FP04145
Submitted: 13 August 2004 Accepted: 17 November 2004 Published: 24 February 2005
Abstract
Elongation of primary roots of azuki bean (Vigna angularis Ohwi et Ohashi) was suppressed under hypergravity conditions produced by centrifugation, such that the growth rate decreased in proportion to the logarithm of the magnitude of the gravity. The removal of the root cap did not influence the hypergravity-induced inhibition of root growth, although it completely inhibited the gravitropic root curvature. Lanthanum and gadolinium, blockers of mechanoreceptors, nullified the growth-inhibitory effect of hypergravity. These results suggest that the gravity signal for the hypergravity-induced inhibition of root growth is perceived independently from that of gravitropism, which involves amyloplasts as statoliths. Horizontal and basipetal hypergravity suppressed root growth as did acropetal hypergravity, all of which were nullified by the presence of lanthanum or gadolinium. These findings suggest that mechanoreceptors on the plasma membrane perceive the gravity signal independently of the direction of the stimuli and roots may utilise it to regulate their growth rate.
Keywords: azuki bean, graviperception, growth inhibition, hypergravity, mechanoreceptor, roots, Vigna angularis.
Acknowledgments
We thank Professor Emeritus Yoshio Masuda of Osaka City University for invaluable suggestions and discussions. The present study was supported in part by a Grant for Ground Research for Space Utilisation from the Japan Space Forum.
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