LIGAND-GATED CA2-PLANTS( CHANNELS AND CA2+ SIGNALING IN HIGHER)

Ligand-gated Ca2+ channels provide a possible mechanism for linking pe rception of stimuli to intracellular Ca2+ mobilization. Evidence for l igand-gated Ca2+ release in plant cells arises from radiolabelled liga nd 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 (InsP(3 )) and the second is gated by cyclic adenosine 5'-diphosphoribose (cAD PR), Previous biochemical studies on plant InsP(3) binding sites have been hampered by tow density of specific binding. The present work rep orts optimization of yield for solubilized InsP(3) binding sites with respect to detergent type and concentration, and the originating tissu e. Further studies reveal a pharmacological similarity between cADPR-a ctivated Ca2+ release in plant and animal cells and demonstrate that t he extent of cADPR-induced Ca2+ release is dependent on the plant tiss ue type. In animal cells cADPR releases Ca2+ through activation of at least one isoform of the so-called ryanodine receptor. It is shown her e that ryanodine itself is able to activate single channel currents in vacuolar membranes. These observations are integrated into current mo dels for ligand-gated Ca2+ release in plant and animal cells and their role in Ca2+-based cell signalling.