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Plant Physiology Preview Published on July 27, 2007; 10.1104/pp.107.102624
Received May 21, 2007 Effect of Secondary Metabolites Associated with Anaerobic Soil Conditions on Ion Fluxes and Electrophysiology in Barley Roots
School of Agricultural Science and Tasmanian Institute of Agricultural Research, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia * Corresponding author; email: Sergey.Shabala{at}utas.edu.au.
The effects of secondary metabolites produced by waterlogged soils on net K+, H+ and Ca2+ fluxes were studied in the mature zone of roots of two barley (Hordeum vulgare L.) cultivars contrasting in their waterlogging (WL) tolerance using the non-invasive MIFE ion flux measuring technique. In WL-sensitive variety Naso Nijo, all three lower monocarboxylic acids (formic, acetic and propionic acids) and three phenolic acids (benzoic, 2-hydroxybenzoic, 4-hydroxybenzoic acids) caused a substantial shift towards steady K+ efflux, accompanied by an immediate net influx of H+. Detrimental effects of secondary metabolites on K+ homeostasis in root cells were absent in WL-tolerant TX variety. Root treatment with Mn2+ caused only a temporary K+ loss that returned to the initial level 10 min after treatment. Phenolic acids slightly increased Ca2+ influx immediately after treatment, while other metabolites tested resulted in transient Ca2+ efflux from the root. In the long-term (24 h) treatment, all metabolites tested significantly reduced K+ uptake, and the adverse effects of phenolic acids were smaller than for monocarboxylic acids and Mn2+. Treatment with monocarboxylic acids for 24 h shifted H+ from net efflux to net influx, while all three phenolic acids did not cause significant effects compared with the control. Based on results of pharmacological experiments and membrane potential measurements, a model explaining the effects of secondary metabolites on membrane transport activity is proposed. We also suggest that plant tolerance to these secondary metabolites could be considered a useful trait in breeding programs.
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