Guard cell cation channels are involved in Na+–induced stomatal closure in a halophyte

Authors

  • Anne-Aliénor Véry,

    1. The Plant Laboratory, Department of Biology, University of York, PO Box 373, York Y01 5YW, UK, and, Department of Biological Sciences, Institute of Environmental and Natural Sciences, University of Lancaster, Lancaster LA1 4YQ, UK
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  • Michael F. Robinson,

    1. The Plant Laboratory, Department of Biology, University of York, PO Box 373, York Y01 5YW, UK, and, Department of Biological Sciences, Institute of Environmental and Natural Sciences, University of Lancaster, Lancaster LA1 4YQ, UK
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  • Terry A. Mansfield,

    1. The Plant Laboratory, Department of Biology, University of York, PO Box 373, York Y01 5YW, UK, and, Department of Biological Sciences, Institute of Environmental and Natural Sciences, University of Lancaster, Lancaster LA1 4YQ, UK
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  • Dale Sanders

    1. The Plant Laboratory, Department of Biology, University of York, PO Box 373, York Y01 5YW, UK, and, Department of Biological Sciences, Institute of Environmental and Natural Sciences, University of Lancaster, Lancaster LA1 4YQ, UK
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Summary

The halophyte Aster tripolium, unlike well-studied non-halophytic species, partially closes its stomata in response to high Na+ concentrations. Since A. tripolium possesses no specific morphological adaptation to salinity, this stomatal response, preventing excessive accumulation of Na+ within the shoot via control of the transpiration rate, is probably a principal feature of its salt tolerance within the shoot. The ionic basis of the stomatal response to Na+ was studied in guard cell protoplasts from A. tripolium and from a non-halophytic relative, Aster amellus, which exhibits classical stomatal opening on Na+. Patch-clamp studies revealed that plasma membrane K+ channels (inward and outward rectifiers) of the halophytic and the non-halophytic species are highly selective for K+ against Na+, and are very similar with respect to unitary conductance and direct sensitivity to Na+. On the other hand, both species possess a significant permeability to Na+ through non-rectifying cation channels activated by low (physiological) external Ca2+ concentrations. Finally, it appeared that the differential stomatal response between the two species is achieved, at least in part, by a Na+-sensing system in the halophyte which downregulates K+ uptake. Thus, increases in guard cell cytosolic Na+ concentration in A. tripolium but not in A. amellus, lead to a delayed (20–30 min) and dramatic deactivation of the K+ inward rectifier. This deactivation is probably mediated by an increase in cytosolic Ca2+ since buffering it abolishes the response. The possible role of K+ inward rectifiers in the response of A. tripolium’s stomata to Na+, suggested by patch-clamp studies, was confirmed by experiments demonstrating that specific blockade of inward rectifying channels mimics Na+ effects on stomatal aperture, and renders aperture refractory to Na+.

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