Effect of the General Anaesthetic Ketamine on Electrical and Ca²⁺ Signal Propagation in Arabidopsis thaliana

The systemic electrical signal propagation in plants (i.e., from leaf to leaf) is dependent on GLUTAMATE RECEPTOR-LIKE proteins (GLRs). The GLR receptors are the homologous proteins to the animal ionotropic glutamate receptors (iGluRs) which are ligand-gated non-selective cation channels that mediate neurotransmission in the animal's nervous system. In this study, we investigated the effect of the general anaesthetic ketamine, a well-known non-competitive channel blocker of human iGluRs, on systemic electrical signal propagation in Arabidopsis thaliana. We monitored the electrical signal propagation, intracellular calcium level [Ca2+](cyt) and expression of jasmonate (JA)-responsive genes in response to heat wounding. Although ketamine affected the shape and the parameters of the electrical signals (amplitude and half-time, t(1/2)) mainly in systemic leaves, it was not able to block a systemic response. Increased [Ca2+](cyt) and the expression of jasmonate-responsive genes were detected in local as well as in systemic leaves in response to heat wounding in ketamine-treated plants. This is in contrast with the effect of the volatile general anaesthetic diethyl ether which completely blocked the systemic response. This low potency of ketamine in plants is probably caused by the fact that the critical amino acid residues needed for ketamine binding in human iGluRs are not conserved in plants' GLRs.