Electrical and chemical signals involved in short-term systemic photosynthetic responses of tobacco plants to local burning
ABSTRACT Short-term (up to 1h) systemic responses of tobacco (Nicotiana tabacum cv. Samsun) plants to local burning of an upper leaf were studied by measuring the following variables in a distant leaf: extracellular electrical potentials (EEPs); gas exchange parameters; fast chlorophyll fluorescence induction; and endogenous concentrations of three putative chemical signaling compounds—abscisic (ABA), jasmonic (JA), and salicylic (SA) acids. The first detected response to local burning in the distant leaves was in EEP, which started to decline within 10–20s of the beginning of the treatment, fell sharply for ca. 1–3min, and then tended to recover within the following hour. The measured gasometric parameters (stomatal conductance and the rates of transpiration and CO2 assimilation) started to decrease 5–7min after local burning, suggesting that the electrical signals may induce stomatal closure. These changes were accompanied by systemic increases in the endogenous ABA concentration followed by huge systemic rises in endogenous JA levels started after ca. 15min, providing the first evidence of short-term systemic accumulation of these plant hormones in responses to local burning. Furthermore, JA appears to have an inhibitory effect on CO2 assimilation. The correlations between the kinetics of the systemic EEP, stomatal, photosynthetic, ABA, and JA responses suggest that (1) electrical signals (probably induced by a propagating hydraulic signal) may trigger chemical defense-related signaling pathways in tobacco plants; (2) both electrical and chemical signals are interactively involved in the induction of short-term systemic stomatal closure and subsequent reductions in the rate of transpiration and CO2 assimilation after local burning events.