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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Effect of Secondary Metabolites Associated with Anaerobic Soil Conditions on Ion Fluxes and Electrophysiology in Barley Roots^1,[C]

School of Agricultural Science and Tasmanian Institute of Agricultural Research, University of Tasmania, Hobart, Tasmania 7001, Australia

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) cultivars contrasting in their waterlogging (WL) tolerance using the noninvasive microelectrode 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 toward 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.

² Present address: School of Plant Biology (MO84), University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Sergey Shabala (sergey.shabala{at}utas.edu.au).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.102624

^* Corresponding author; e-mail sergey.shabala{at}utas.edu.au.

Received May 21, 2007; accepted July 23, 2007; published July 27, 2007.

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On the Inside

Peter V. Minorsky
Plant Physiol. 2007 145: 1-2. [Full Text]