Analysis of the Transient Increase in Cytosolic Ca during the Action Potential of Higher Plants with High Temporal Resolution: Requirement of Ca Transients for Induction of Jasmonic Acid Biosynthesis and PINII Gene Expression

; Plants respond to various abiotic stimuli by activation and propagation of fast electrical signals, action potentials. To resolve the temporal increase in cytosolic Ca during the action potentials of higher plants, we regenerated transgenic potato plants that expressed the Ca photoprotein apoaequorin. These genetically engineered potato plants were used for simultaneous measurements of transient changes in the membrane potential and the Ca luminescence triggered by heat-induced action potentials. High temporal resolution for recording of the fast transient electrical and light signals was accomplished by a sampling rate of 1 kHz. Upon elicitation by heat the membrane potential depolarization preceded the rise of cytosolic Ca by 50–100 ms. Several Ca channel blockers were tested to inhibit the rise in cytosolic Ca. Treatment of plants with Ruthenium Red blocked the elevation in cytosolic Ca that was associated with heat-stimulated action potentials. Furthermore, action potentials have been demonstrated to stimulate jasmonic acid biosynthesis and PINII gene expression. Therefore, we measured jasmonic acid and PINII gene expression levels subsequent to action potential initiation by a short heating pulse. As expected, jasmonic acid biosynthesis and PINII gene expression were induced by action potentials. Pretreatment of potato plants with Ruthenium Red inhibited induction of jasmonic acid biosynthesis and PINII gene expression that was generally triggered by heat-activated action potentials.