Journal Article

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

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 3, pages 619-631
Published in print February 2008 | ISSN: 0022-0957
Published online February 2008 | e-ISSN: 1460-2431 | DOI:

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The apoplastic pH of intact Forsythia×intermedia (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.

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

Journal Article.  7956 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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