Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Published on September 3, 2008; 10.1104/pp.108.125518

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Received June 28, 2008
Accepted August 26, 2008

The regulation of cell wall extensibility during shade avoidance: a study using two contrasting ecotypes of Stellaria longipes

Rashmi Sasidharan , C C Chinnappa , Laurentius A C J Voesenek *, and Ronald Pierik

Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands; Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada

* Corresponding author; email: L.A.C.J.Voesenek{at}uu.nl.

Shade avoidance in plants involves rapid shoot elongation to grow towards 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 prairie ecotype of Stellaria longipes differing in their response to shade, to study regulation of cell wall extensibility in response to low red to far-red ratio (R/FR), an early neighbour detection signal and dense canopy shade (green shade: low R/FR, blue and total light intensity). Alpine plants were non-responsive 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 that 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.






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