Signalling mechanisms involved in the response of two varieties of Humulus lupulus L. to soil drying: II. changes in the concentration of abscisic acid catabolites and stress-induced phytohormones
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Abscisic acid (ABA) is one of the most common stress signals that appear in plant organs in response to soil drying. Equilibrium between ABA biosynthesis and catabolism regulates ABA accumulation in plants under water stress. The aim of our work was to explore the dynamics of changes in ABA metabolites as well as other stress-induced phytohormones such as jasmonic acid, indole-3-acetic acid, and their respective metabolites in hop [Humulus lupulus (L.)] plants during drying and to identify among them potential signals involved in drought signalling. We showed that the concentrations of all ABA metabolites (except the concentration of ABA glucosyl ester in leaves) increased in the same manner in leaves and xylem sap approximately at the same level of soil water content when the relative water content of leaves decreased. The predominant metabolites in leaves and xylem sap were phaseic acid and dihydroxyphaseic acid. ABA glucosyl ester was not a source of the increased concentration of ABA in leaves and xylem sap because of its considerably lower concentration compared to ABA. The concentration of jasmonates decreased in leaves of hop plants. Changes in auxin concentration suggest that this hormone is involved in the response of hop plants to soil drying.
KeywordsABA metabolites ABAGE Hop Jasmonic acid Relative water content
Abscisic acid glucosyl ester
Indole-3-acetic acid aspartate
Jasmonic acid isoleucine
Relative water content
Stem water potential
The authors would like to thank Oldřich Jůza and Helena Steigerová for help with experimental work; Marie Vitásková and Petra Amakorová for help with ABA metabolite and stress induced phyhormone analyses; Petr Svoboda from the Hop Research Institute in Žatec for providing the plant material; and Matthew Nicholls for proofreading. This work was supported by projects no. 206/09/1967 and GA14-34792S from the Czech Science Foundation. 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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