Manipulation of the apoplastic pH of intact plants mimics stomatal and
growth responses to water availability and microclimatic variation
William J. Davies
The Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK
An open access article from Journal of Experimental Botany 2008 59(3):619-631.
The apoplastic pH of intact Forsythiaxintermedia (cv. Lynwood)and tomato (Solanum lycopersicum) plants has been manipulatedusing 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 thegs and/or leaf growth rate subsequently measured. The most alkalinepH that was applied corresponds to that measured in sap extractedfrom 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 gsdetermined in well-watered Forsythia plants exposed to a naturallyvarying summer microclimate was eliminated by spraying the plantswith relatively alkaline but not acidic buffers, providing evidencefor a novel pH-based signalling mechanism linking the aerialmicroclimate with stomatal aperture. Increasing the pH of thefoliar spray only reduced gs in plants of the abscisic acid(ABA)-deficient flacca mutant of tomato when ABA was simultaneouslysprayed onto leaves or injected into stems. In well-wateredForsythia(variable PFD, VPD, and temperature), xylem pH and leaf ABAconcentration fluctuated but were positively correlated. Manipulationof foliar apoplastic pH also affected the response of gs andleaf growth to ABA injected into stems of intact ForsythiaThe techniques used here to control physiology and water usein intact growing plants could easily be applied in a horticulturalcontext. plants exposed to a naturally varying summer microclimate plants.
Key words: Abscisic acid (ABA), apoplast, leaf growth, pH, soil drying,
stomatal conductance, stomatal guard cells, temperature, vapour
pressure deficit (VPD), xylem