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(American Journal of Botany. 2009;96:652-660.) doi: 10.3732/ajb.0800261 © 2009 Botanical Society of America, Inc.

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Gravity control of growth form in Brassica rapa and Arabidopsis thaliana (Brassicaceae): Consequences for secondary metabolism¹

² Department of Plant Science, University of Connecticut, Storrs, Connecticut 06269 USA ³ Dynamac Corp., Kennedy Space Center, Florida 32899 USA ⁴ Department of Biology, University of Texas Pan American, Edinburg, Texas 78539 USA ⁵ DESC @ OCB-ACTA, Vrije Universiteit and University of Amsterdam, Amsterdam, The Netherlands

ABSTRACT

How gravity influences the growth form and flavor components of plants is of interest to the space program because plants could be used for food and life support during prolonged missions away from the planet, where that constant feature of Earth’s environment does not prevail. We used plant growth hardware from prior experiments on the space shuttle to grow Brassica rapa and Arabidopsis thaliana plants during 16-d or 11-d hypergravity treatments on large-diameter centrifuge rotors. Both species showed radical changes in growth form, becoming more prostrate with increasing g-loads (2-g and 4-g). In Brassica, height decreased and stems thickened in a linear relationship with increasing g-load. Glucosinolates, secondary compounds that contribute flavor to Brassica, decreased by 140% over the range of micro to 4-g, while the structural secondary compound, lignin, remained constant at 15% (w/w) cell wall dry mass. Stem thickening at 4-g was associated with substantial increases in cell size (47%, 226%, and 33% for pith, cortex, and vascular tissue), rather than any change in cell number. The results, which demonstrate the profound effect of gravity on plant growth form and secondary metabolism, are discussed in the context of similar thigmostresses such as touch and wind.

Key Words: Arabidopsis thaliana • Brassica rapa • Brassicaceae • centrifuge • glucosinolates • hypergravity • lignin • plant growth

Received for publication 28 July 2008. Accepted for publication 10 November 2008.

FOOTNOTES

¹ The authors thank M. Regan, A. Spinale, B. Wells, H. Levine, D. Shultz, and D. Gruendel from Kennedy Space Center, FL; Tom Luzod, T. Shaw, and J. Rask at Ames Research Center, Moffett Field, CA, and R. Wagers-Hughes and Erica Escobeda from UT Pan American, for supporting the experiments. This project was funded by NASA grants NAG10-329 and NNX07AT77G to M.E.M. and by NWO-ALW-SRON grant MG-057 to J.v.L.

⁶ Author for correspondence (e-mail: mary.musgrave{at}uconn.edu)

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