Stomatal Responses to Abscisic Acid in Natural Environments

Abstract

The role of abscisic acid (ABA) as a stress hormone has been well established through greenhouse and laboratory studies. This paper reports the results of studies investigating the role of ABA under natural stress conditions in (1) almond trees (Prunus dulcis) and several desert plants (including Anastatica hierochuntica, Hammada scoparia and Zygophyllum dumosum) in the Negev Desert, Israel, (2) Ceanothus thyrsiflorus and Chilopsis linearis shrubs in the Chapparall in S. California, and (3) Prunus avium and Cornus sanguineum [C. sanguinea] from a steep, dry, sun exposed slope in the Main Valley in Germany. Xylem sap ABA, water potential and leaf conductance were measured in all studies. ABA concentrations increased slowly with decreasing water potential until a threshold was reached and then increased quickly. In some cases there was only a clear relation between predawn water potential (a measure of soil water potential) and xylem sap ABA. In another experiment, ABA was injected into the veins of cotton [Gossypium] leaves grown in open-top chambers at high CO2 concentrations (650 жl/litre) under highly stressed field conditions in Arizona and stomatal conductance was measured. The results indicated that under increased CO2 conditions the stomata reacted more rapidly to ABA injections than under ambient conditions. It is concluded that ABA plays an important stress-physiological role as a root-shoot signal influencing stomatal responses to environmental perturbations under natural conditions.