Premium
Osmotic stress enhances the competence of Beta vulgaris vacuoles to respond to inositol 1,4,5‐trisphosphate
Author(s) -
Allen Gethyn J.,
Sanders Dale
Publication year - 1994
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1994.6050687.x
Subject(s) - vacuole , inositol , cytosol , biophysics , osmotic shock , inositol trisphosphate , intracellular , microbiology and biotechnology , biology , patch clamp , biochemistry , chemistry , cytoplasm , receptor , enzyme , gene
Summary Isolated vacuoles from Beta vulgaris storage roots respond to the intracellular signalling molecule inositol 1,4,5‐trisphosphate (InsP 3 ). Whole vacuole patch clamp enables measurement of an inward current (cytosol‐directed) induced by cytosolic InsP 3 which is fully reversible upon removal of InsP 3 . The reversal potentials of the InsP 3 ‐induced whole vacuolar currents indicate a permeability ratio ( P,Ca : P,K ) of 200:1. Competence of vacuoles to respond to InsP 3 is dependent upon the root tissue undergoing hyperosmotic stress before vacuole isolation. The magnitude of the hyperosmotic stress and the density of InsP 3 ‐induced current per unit membrane area are exponentially related. A standing osmotic gradient across the vacuolar membrane further enhances the InsP 3 ‐induced current, the current being larger when there is net water flux from the cytosol to the vacuolar lumen. InsP 3 ‐induced currents are not affected by the cytosolic free Ca 2+ concentration. The conductance of InsP 3 ‐induced single channel currents varied greatly between individual outside‐out patches, but all showed a non‐linear increase in single channel current at physiological potentials. The reversal potentials of these currents indicated a P Ca :P K of between 100:1 and 800:1. The significance of these findings is discussed in relation to technical aspects of monitoring InsP 3 ‐induced currents in plant vacuoles and in the context of the physiological roles of InsP 3 and its receptor in cell water relations.