Ligand-gated Ca²⁺ channels and Ca²⁺ signalling in higher plants
1997
Muir, Shelagh R. | Bewell, Michael A. | Sanders, D (Dale) | Allen, Gethyn J.
Ligand-gated Ca²⁺ channels provide a possible mechanism for linking perception of stimuli to intracellular Ca²⁺ mobilization. Evidence for ligand-gated Ca²⁺ release in plant cells arises from radiolabeled ligand binding, microsomal ion flux, and electrophysiological approaches. Results from these diverse approaches demonstrate that two classes of ligand-gated channels are present at the plant cell vacuolar membrane. One class of channel is gated by inositol 1,4,5 trisphosphate (InsP₃) and the second is gated by cyclic adenosine 5'-diphosphoribose (cADPR). Previous biochemical studies on plant InsP₃ binding sites have been hampered by low density of specific binding. The present work reports optimization of yield for solubilized InsP₃ binding sites with respect to detergent type and concentration, and the originating tissue. Further studies reveal a pharmacological similarity between cADPR-activated Ca²⁺ release in plant and animal cells and demonstrate that the extent of cADPR-induced Ca²⁺ release is dependent on the plant tissue type. In animal cells cADPR releases Ca²⁺ through activation of at least one isoform of the so-called ryanodine receptor. It is shown here that ryanodine itself is able to activate single channel currents in vacuolar membranes. These observations are integrated into current models for ligand-gated Ca²⁺ release in plant and animal cells and their role in Ca²⁺-based cell signalling.
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