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Effects of Xylem pH on Transpiration from Wild-Type and flacca Tomato Leaves¹
A Vital Role for Abscisic Acid in Preventing Excessive Water Loss Even from Well-Watered Plants

Sally Wilkinson^*, Janet E. Corlett, Ludovic Oger, and William J. Davies

Institute of Environmental and Natural Sciences, Lancaster University, Bailrigg, Lancaster, LA1 4YQ, United Kingdom, (S.W., W.J.D.); and Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, United Kingdom (J.E.C., L.O.)

The pH of xylem sap from tomato (Lycopersicon esculentum) plants increased from pH 5.0 to 8.0 as the soil dried. Detached wild-type but not flacca leaves exhibited reduced transpiration rates when the artificial xylem sap (AS) pH was increased. When a well-watered concentration of abscisic acid (0.03 µM) was provided in the AS, the wild-type transpirational response to pH was restored to flacca leaves. Transpiration from flacca but not from wild-type leaves actually increased in some cases when the pH of the AS was increased from 6.75 to 7.75, demonstrating an absolute requirement for abscisic acid in preventing stomatal opening and excessive water loss from plants growing in many different environments.

Plant Physiol. (1998) 117: 703-709
Copyright Clearance Center:   0032-0889/98/117/0703/07
© 1998 American Society of Plant Physiologists

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