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JXB Advance Access originally published online on February 13, 2008
Journal of Experimental Botany 2008 59(3):619-631; doi:10.1093/jxb/erm338
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Manipulation of the apoplastic pH of intact plants mimics stomatal and growth responses to water availability and microclimatic variation

Sally Wilkinson* and William J. Davies

The Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK

* To whom correspondence should be addressed. E-mail: sally.wilkinson{at}lancaster.ac.uk

The apoplastic pH of intact Forsythiaxintermedia (cv. Lynwood) and tomato (Solanum lycopersicum) plants has been manipulated using buffered foliar sprays, and thereby stomatal conductance (gs), leaf growth rate, and plant water loss have been controlled. The more alkaline the pH of the foliar spray, the lower the gs and/or leaf growth rate subsequently measured. The most alkaline pH that was applied corresponds to that measured in sap extracted from shoots of tomato and Forsythia plants experiencing, respectively, soil drying or a relatively high photon flux density (PFD), vapour pressure deficit (VPD), and temperature in the leaf microclimate. The negative correlation between PFD/VPD/temperature and gs determined in well-watered Forsythia plants exposed to a naturally varying summer microclimate was eliminated by spraying the plants with relatively alkaline but not acidic buffers, providing evidence for a novel pH-based signalling mechanism linking the aerial microclimate with stomatal aperture. Increasing the pH of the foliar spray only reduced gs in plants of the abscisic acid (ABA)-deficient flacca mutant of tomato when ABA was simultaneously sprayed onto leaves or injected into stems. In well-watered Forsythia plants exposed to a naturally varying summer microclimate (variable PFD, VPD, and temperature), xylem pH and leaf ABA concentration fluctuated but were positively correlated. Manipulation of foliar apoplastic pH also affected the response of gs and leaf growth to ABA injected into stems of intact Forsythia plants. The techniques used here to control physiology and water use in intact growing plants could easily be applied in a horticultural context.

Key words: Abscisic acid (ABA), apoplast, leaf growth, pH, soil drying, stomatal conductance, stomatal guard cells, temperature, vapour pressure deficit (VPD), xylem

Received 17 October 2007; Revised 28 November 2007 Accepted 30 November 2007


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