Plant species developed some systemic self-protecting mechanisms inducible by local stress. Some questions about the nature of moving signals and their connection to systemic changes in the energetic processes including photosynthesis are still unresolved.
A short-term systemic response of tobacco plants (Nicotiana tabacum cv. Samsun ) to local burning was investigated. A basipetal spreading of electrical signal along the plant, evoked by the local burning of the upper leaf, was detected by changes in the extracellular electrical potential differences (EEPD) between Ag/AgCl electrodes placed on three untreated leaves and a reference electrode placed in the root nutrient solution. Simultaneously, the photosynthetic parameters (gas exchange and chlorophyll fluorescence) were measured on the selected leaves. Concentrations of potential chemical signal compounds - jasmonic (JA) and abscisic acid ( ABA ) - in measured leaves were measured by the LC-MS method.
Changes in EEPD were observed in several seconds after burning depending on the distance from the site of burning. The extent of EEPD changes was mostly within 10 - 70 mV. Main changes lasted several minutes and a steady state value was achieved in about 1 hour. In most cases the amplitude of changes decreased with increasing distance of the measured leaf from the burned one. The propagation velocity was about 1 cm s^-1. The EEPD changes were followed in several minutes by a pronounced decrease in the rate of CO₂ assimilation, transpiration and stomatal conductance. Nearly no change was detectable in the sub-stomatal concentration of CO₂. Similarly, negligible short-term changes in chlorophyll fluorescence induction and photochemical quenching were detectable. In the measured leaves, also changes in JA and ABA concentrations were observed.
We suggest that the short-term changes in photosynthesis evoked by local burning are stimulated (directly or indirectly) by the moving electrical signal. Interestingly, these photosynthesis changes do not include changes of electron transport in PSII.

Acknowledgements. The project has been supported by grant from Ministry of Education of the Czech Republic , No. MSM 6198959215.