Signalling mechanisms involved in the response of two varieties of Humulus lupulus L. to soil drying: I. changes in xylem sap pH and the concentrations of abscisic acid and anions
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Background and aims
Soil drying leads to the generation of chemical signals in plants that regulate water use via control of the stomatal aperture. The aim of our work was to identify the presence and identity of potential chemical signals, their dynamics, and their relationship with transpiration rate during soil drying in hop (Humulus lupulus (L.)) plants.
We used pressure chamber technique for measurement of shoot water potential and collection of shoot xylem sap. We analyzed concentrations of abscisic acid (ABA), nitrate, phosphate, sulphate and malate in sap and also the rate of whole plant transpiration.
Transpiration rate decreased prior to changes in shoot water potential. The concentration of ABA in xylem sap continuously increased from early to later stages of water stress, whereas in leaves it increased only at later stages. Shoot sap pH increased simultaneously with the decrease of transpiration rate. Xylem sap alkalization was in some cases accompanied by a decrease in nitrate concentration and an increase in malate concentration. Concentration of sulphate increased in xylem sap during drying and sulphate in combination with a higher ABA concentration enhanced stomatal closure.
Several early chemical signals appear in sap of hop plants during soil drying and their impact on transpiration may vary according to the stage of soil drying.
KeywordsAbscisic acid (ABA) Hops Malate Sulphate Transpiration rate
Stem water potential
Soil water content
The authors would like to thank Helena Steigerová and Martina Fojtů for help with experimental work, Marie Vitásková and Petra Amakorová for ABA purification, and Petr Svoboda from the Hop Research Institute in Žatec for providing the plant material. This work was supported by project no. 206/09/1967 from the Czech Science Foundation and by the Internal Grant Agency of Palacký University (IGA_PrF_2014006). We also would like to thank two anonymous reviewers for their comments and recommendations, which helped us improve the manuscript considerably.
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