Magnesium sensitizes slow vacuolar channels to physiological cytosolic calcium and inhibits fast vacuolar channels in fava bean guard cell vacuoles

Journal Article (Journal Article)

Vacuolar ion channels in guard cells play important roles during stomatal movement and are regulated by many factors including Ca , calmodulin, protein kinases, and phosphatases. We report that physiological cytosolic and luminal Mg levels strongly regulate vacuolar ion channels in fava bean (Vicia faba) guard cells. Luminal Mg inhibited fast vacuolar (FV) currents with a K of approximately 0.23 mM in a voltage-dependent manner at positive potentials on the cytoplasmic side. Cytosolic Mg at 1 mM also inhibited FV currents. Furthermore, in the absence of cytosolic Mg , cytosolic Ca at less than 10 μM did not activate slow vacuolar (SV) currents. However, when cytosolic Mg was present, submicromolar concentrations of cytosolic Ca activated SV currents with a K(d) of approximately 227 nM, suggesting a synergistic Mg -Ca effect. The activation potential of SV currents was shifted toward physiological potentials in the presence of cytosolic Mg concentrations. The direction of SV currents could also be changed from outward to both outward and inward currents. Our data predict a model for SV channel regulation, including a cytosolic binding site for Ca with an affinity in the submicromolar range and a cytosolic low-affinity Mg -Ca binding site. SV channels are predicted to contain a third binding site on the vacuolar luminal side, which binds Ca and is inhibitory. In conclusion, cytosolic Mg sensitizes SV channels to physiological cytosolic Ca elevations. Furthermore, we propose that cytosolic and vacuolar Mg concentrations ensure that FV channels do not function as a continuous vacuolar K leak, which would prohibit stomatal opening. 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ + 1

Full Text

Duke Authors

Cited Authors

  • Pei, ZM; Ward, JM; Schroeder, JI

Published Date

  • January 1, 1999

Published In

Volume / Issue

  • 121 / 3

Start / End Page

  • 977 - 986

International Standard Serial Number (ISSN)

  • 0032-0889

Digital Object Identifier (DOI)

  • 10.1104/pp.121.3.977

Citation Source

  • Scopus