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AOBPreview published online on March 14, 2006
Annals of Botany, doi:10.1093/aob/mcl055
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received September 26, 2005
Revised December 9, 2005
Accepted February 8, 2006

Article

Hypergravity Stimulus Enhances Primary Xylem Development and Decreases Mechanical Properties of Secondary Cell Walls in Inflorescence Stems of Arabidopsis thaliana

IZUMI NAKABAYASHI 1 {dagger}, ICHIROU KARAHARA 1 * {dagger}, DAISUKE TAMAOKI 1, KYOJIRO MASUDA 1, TATSUYA WAKASUGI 1, KYOJI YAMADA 1, KOUICHI SOGA 2, TAKAYUKI HOSON 2, and SEIICHIRO KAMISAKA 1

1 Department of Biology, Faculty of Science, Toyama University, Toyama, 930-8555, Japan
2 Graduate School of Science, Osaka City University, Sumiyoshi-ku, 558-8585, Osaka, Japan

* To whom correspondence should be addressed.
ICHIROU KARAHARA, E-mail: karahara{at}sci.toyama-u.ac.jp


  Abstract

• Background and Aims The xylem plays an important role in strengthening plant bodies. Past studies on xylem formation in tension woods in poplar and also in clinorotated Prunus tree stems lead to the suggestion that changes in the gravitational conditions affect morphology and mechanical properties of xylem vessels. The aim of this study was to examine effects of hypergravity stimulus on morphology and development of primary xylem vessels and on mechanical properties of isolated secondary wall preparations in inflorescence stems of arabidopsis.

• Methods Morphology of primary xylem was examined under a light microscope on cross-sections of inflorescence stems of arabidopsis plants, which had been grown for 3-5 d after exposure to hypergravity at 300 g for 24 h. Extensibility of secondary cell wall preparation, isolated from inflorescence stems by enzyme digestion of primary cell wall components (mainly composed of metaxylem elements), was examined. Plants were treated with gadolinium chloride, a blocker of mechanoreceptors, to test the involvement of mechanoreceptors in the responses to hypergravity.

• Key Results Number of metaxylem elements per xylem, apparent thickness of the secondary thickenings, and cross-section area of metaxylem elements in inflorescence stems increased in response to hypergravity. Gadolinium chloride suppressed the effect of hypergravity on the increase both in the thickness of secondary thickenings and in the cross-section area of metaxylem elements, while it did not suppress the effect of hypergravity on the increase in the number of metaxylem elements. Extensibility of secondary cell wall preparation decreased in response to hypergravity. Gadolinium chloride suppressed the effect of hypergravity on cell wall extensibility.

• Conclusions Hypergravity stimulus promotes metaxylem development and decreases extensibility of secondary cell walls, and mechanoreceptors were suggested to be involved in these processes.

Keywords: Arabidopsis thaliana, metaxylem, protoxylem, hypergravity, mechanoreceptor, secondary cell wall, secondary thickening, mechanical property, cell wall extensibility.
{dagger} These authors made equal contributions to this work.
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