Unique ethylene-regulated touch responses of Arabidopsis thaliana roots to physical hardness |
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Authors: | Chigusa Yamamoto Yoichi Sakata Teruaki Taji Tadashi Baba Shigeo Tanaka |
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Affiliation: | (1) Faculty of Applied Bioscience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan;(2) Faculty of Agriculture, Tokyo University of Agriculture, 1737 Funako, Atsugi Kanagawa, 243-0034, Japan |
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Abstract: | Although touch responses of plant roots are an important adaptive behavior, the molecular mechanism remains unclear. We have developed a bioassay for measuring root-bending responses to physical hardness in Arabidopsis thaliana seedlings. Our test requires a two-layer solid medium. Primary roots growing downward through an upper layer of 0.3% phytagel either penetrate the lower layer or bend along an interface between the upper and lower layers with different concentrations (0.2–0.5%, corresponding to 1.57–6.79 gw mm−2 in hardness). In proportion to increasing hardness of the lower layer, we found that the percentage of bending roots increased and ethylene production decreased, suggesting an inverse relationship between the root-bending response and ethylene production. Studies with ethylene biosynthesis modulators and mutants also suggested that bending and non-bending responses of roots to medium hardness depend, respectively, on decreased and increased ethylene biosynthesis. In addition, the degrees of root-tip softening and differential root-cell growth, both possible factors determining root-bending response, were enhanced and attenuated by decreased and increased amounts of ethylene, respectively—also in bending roots and non-bending roots. Our findings indicate that ethylene regulates root touch responses, probably through a combination of root-tip softening (or hardening) and differential root-cell growth. |
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Keywords: | Arabidopsis thaliana Cell growth Ethylene Rigidity Thigmotropism Touch response |
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