Hydrotropism and Auxin-Inducible Gene expression in Roots Grown Under Microgravity Conditions (HydroTropi) - 07.15.14
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Science Objectives for Everyone Hydrotropism and Auxin-Inducible Gene expression in Roots Grown Under Microgravity Conditions (HydroTropi) determines whether hydrotropic response can be used for the control of cucumber, Cucumis sativus root growth orientation in microgravity.
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Gravity wins on Earth but water wins in space. This investigation examine the effects of gravity and water on cucumber roots to determine which response rules: hydrotropism – response to water – or gravitropism – response to gravity. Measurement of the growth and curvature of the roots and their gene expression showed that roots bent toward moisture in microgravity but grew straight along the direction of gravitational force at normal gravity. This sensitivity of roots to moisture gradients in microgravity may help regulate root growth for future plant production in space. The results also may help develop technology that enables plants to more efficiently uptake water here on Earth.
Sponsoring Space Agency
Japan Aerospace Exploration Agency (JAXA)
ISS Expedition Duration
March 2010 - March 2011
Previous ISS Missions
Increment 23/24 will be the first mission for HydroTropi operations.
The Hydrotropism and Auxin‐Inducible Gene expression in Roots Grown Under Microgravity Conditions (HydroTropi) experiment has three specific aims:
- First, it demonstrates that gravitropism (a plant's ability to change its direction of growth in response to gravity) interferes with hydrotropism (a directional growth response in which the direction is determined by a stimuli in water concentration).
- Second, it clarifies the differential auxin response that occurs during the respective tropisms (reaction of a plant to a stimulus), by investigating the auxin (compound regulating the growth of plants) inducible gene expression.
- Third, it shows whether hydrotropism can be used in controlling root growth orientation in microgravity.
Hydrotropism and Auxin‐Inducible Gene expression in Roots Grown Under Microgravity Conditions (HydroTropi) will propose to use the microgravity environment in space to separate hydrotropism from gravitropism and to dissect respective mechanisms in cucumber roots.
HydroTropi provides a further understanding of how plants grow and develop at a molecular level, which can lead to significant advancements in agricultural production on Earth.
The on-board experiments were successfully carried out and researchers measured the growth and curvature of the seedling roots and analyzed CsIAA1 expression by in situ hybridization. The results showed that roots hydrotropically bent toward the moistened plastic foam under microgravity conditions, whereas they grew straight along the direction of gravitational force under 1G conditions. The hydrotropic response in microgravity appeared to be greater in the NaCl chamber compared with that in H2O chamber, but they did not differ statistically. Furthermore, CsIAA1 gene differentially expressed in the hydrotropically bending roots; the expression was much greater on the concave side than on the convex side. On the other hand, no asymmetric expression of CsIAA1 in the roots grown under 1G conditions were detected. These results revealed that roots become very sensitive to moisture gradients in microgravity and that auxin redistribution and differential auxin response take place during hydrotropic response. Also, the results imply that the hydrotropic response can be used as a means of root growth regulation for plant production in space.
Yamazaki T, Miyazawa Y, Kobayashi A, Moriwaki T, Fujii N, Takahashi H. MIZ1, an essential protein for root hydrotropism, is associated with the cytoplasmic face of the endoplasmic reticulum membrane in Arabidopsis root cells. FEBS Letters. 2012 February; 586(4): 398-402.
Nakayama M, Kaneko Y, Miyazawa Y, Fujii N, Higashitani N, Wada S, Ishida H, Yoshimoto K, Shirasu K, Yamada K, Nishimura M, Nishimura M, Takahashi H. A possible involvement of autophagy in amyloplast degradation in columella cells during hydrotropic response of Arabidopsis roots. Planta. 2012 April 25; 236(4): 999-1012. DOI: 10.1007/s00425-012-1655-5. PMID: 22532286.
Moriwaki T, Miyazawa Y, Kobayashi A, Takahashi H. Molecular mechanisms of hydrotropism in seedling roots of Arabidopsis thaliana (Brassicaceae). American Journal of Botany. 2013; 100(1): 25-34. DOI: 10.3732/ajb.1200419. PMID: 23263156.
Moriwaki T, Miyazawa Y, Fujii N, Takahashi H. Light and abscisic acid signalling are integrated by MIZ1 gene expression and regulate hydrotropic response in roots of Arabidopsis thaliana. Plant, Cell and Environment. 2012 August; 35(8): 1359-1368. DOI: 10.1111/j.1365-3040.2012.02493.x.
Watanabe C, Fujii N, Yanai K, Hotta T, Kim D, Kamada M, Sasagawa-Saito Y, Nishimura T, Koshiba T, Miyazawa Y, Kim K, Takahashi H. Gravistimulation Changes the Accumulation Pattern of the CsPIN1 Auxin Efflux Facilitator in the Endodermis of the Transition Zone in Cucumber Seedlings. Plant Physiology. 2012 January; 158(1): 239-251. DOI: 10.1104/pp.111.188615.
Miyazawa Y, Moriwaki T, Uchida M, Kobayashi A, Fujii N, Takahashi H. Overexpression of MIZU-KUSSEI1 enhances the root hydrotropic response by retaining cell viability under hydrostimulated conditions in Arabidopsis thaliana. Plant and Cell Physiology. 2012 September 25; 53(11): 1926-1933. DOI: 10.1093/pcp/pcs129. PMID: 23012350.
Ground Based Results Publications
Cucumber roots grew laterally in space following 70 hours in microgravity on STS-95. Image courtesy of JAXA.
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NASA Image: ISS025E007780 - NASA astronaut Shannon Walker, Expedition 25 flight engineer, works with the Japan Aerospace Exploration Agency (JAXA) experiment HydroTropi (Hydrotropism & Auxin-Inducible Gene Expression in Roots Grown under Microgravity Conditions) in the Kibo laboratory of the International Space Station.
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