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First published online July 29, 2009; 10.1104/pp.109.138305

Plant Physiology 151:949-954 (2009)
© 2009 American Society of Plant Biologists

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WHOLE PLANT AND ECOPHYSIOLOGY

New Insights into the Mechanisms of Water-Stress-Induced Cavitation in Conifers

Hervé Cochard*, Teemu Hölttä, Stéphane Herbette, Sylvain Delzon and Maurizio Mencuccini

INRA, UMR 547 PIAF, F–63100 Clermont-Ferrand, France (H.C., S.H.); University Blaise Pascal, UMR 547 PIAF, F–63177 Aubière, France (H.C., S.H.); Department of Forest Ecology, University of Helsinki, Helsinki FIN–00014, Finland (T.H.); University of Bordeaux, UMR BIOGECO, F–33405 Talence, France (S.D.); and School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JN, United Kingdom (M.M.)

Cavitation resistance is a key parameter to understand tree drought tolerance but little is known about the mechanisms of air entry into xylem conduits. For conifers three mechanisms have been proposed: (1) a rupture of pit margo microfibrils, (2) a displacement of the pit torus from its normal sealing position over the pit aperture, and (3) a rupture of an air-water menisci in a pore of the pit margo. In this article, we report experimental results on three coniferous species suggesting additional mechanisms. First, when xylem segments were injected with a fluid at a pressure sufficient to aspirate pit tori and well above the pressure for cavitation induction we failed to detect the increase in sample conductance that should have been caused by torus displacement from blocking the pit aperture or by membrane rupture. Second, by injecting xylem samples with different surfactant solutions, we found a linear relation between sample vulnerability to cavitation and fluid surface tension. This suggests that cavitation in conifers could also be provoked by the capillary failure of an air-water meniscus in coherence with the prediction of Young-Laplace's equation. Within the bordered pit membrane, the exact position of this capillary seeding is unknown. The possible Achilles' heel could be the seal between tori and pit walls or holes in the torus. The mechanism of water-stress-induced cavitation in conifers could then be relatively similar to the one currently proposed for angiosperms.

The author 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) is: Herve Cochard (cochard{at}clermont.inra.fr).

www.plantphysiol.org/cgi/doi/10.1104/pp.109.138305

* Corresponding author; e-mail cochard{at}clermont.inra.fr.

Received March 9, 2009; accepted July 28, 2009; published July 29, 2009.

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