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WHOLE PLANT AND ECOPHYSIOLOGY

The Regulation of Cell Wall Extensibility during Shade Avoidance: A Study Using Two Contrasting Ecotypes of Stellaria longipes^1,[C],[OA]

Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, 3584 CA Utrecht, The Netherlands (R.S., L.A.C.J.V., R.P.); and Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (R.S., C.C.C.)

Shade avoidance in plants involves rapid shoot elongation to grow toward the light. Cell wall-modifying mechanisms are vital regulatory points for control of these elongation responses. Two protein families involved in cell wall modification are expansins and xyloglucan endotransglucosylase/hydrolases. We used an alpine and a prairie ecotype of Stellaria longipes differing in their response to shade to study the regulation of cell wall extensibility in response to low red to far-red ratio (R/FR), an early neighbor detection signal, and dense canopy shade (green shade: low R/FR, blue, and total light intensity). Alpine plants were nonresponsive to low R/FR, while prairie plants elongated rapidly. These responses reflect adaptation to the dense vegetation of the prairie habitat, unlike the alpine plants, which almost never encounter shade. Under green shade, both ecotypes rapidly elongate, showing that alpine plants can react only to a deep shade treatment. Xyloglucan endotransglucosylase/hydrolase activity was strongly regulated by green shade and low blue light conditions but not by low R/FR. Expansin activity, expressed as acid-induced extension, correlated with growth responses to all light changes. Expansin genes cloned from the internodes of the two ecotypes showed differential regulation in response to the light manipulations. This regulation was ecotype and light signal specific and correlated with the growth responses. Our results imply that elongation responses to shade require the regulation of cell wall extensibility via the control of expansin gene expression. Ecotypic differences demonstrate how responses to environmental stimuli are differently regulated to survive a particular habitat.

The authors responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) are: Rashmi Sasidharan (r.sasidharan{at}uu.nl) and Ronald Pierik (r.pierik{at}uu.nl).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.125518

^* Corresponding author; e-mail l.a.c.j.voesenek{at}uu.nl.

Received June 28, 2008; accepted August 26, 2008; published September 3, 2008.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2008 148: 1185-1186. [Full Text]