Analysis of the transient increase in cytosolic Ca2+ during the action potential of higher plants with high temporal resolution: Requirement of Ca2+ 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 Ca2+ during the action potentials of higher plants, we regenerated trans-genic potato plants that expressed the Ca2+, photoprotein apoaequorin. These genetically engineered potato plants were used for simultaneous measurements of transient changes in the membrane potential and the Ca2+, 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 Ca2+ by 50-100 ms. Several Ca2+ channel blockers were tested to inhibit the rise in cytosolic Ca2+. Treatment of plants with Ruthenium Red blocked the elevation in cytosolic Ca2+ 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.