• In the sensitive species Mimosa pudica electric signals arise when the leaves are stimulated by touching or wounding. Experiments reported here provide information about a photosynthetic response that results from heat-induced electrical signalling in leaves. • Electric potential measurements, combined with chlorophyll fluorescence, as well as gas exchange measurements showed that wounding evokes an electrical signal that travels rapidly into the neighbouring leaf pinna to eliminate the net-CO2 uptake rate. At the same time the PSII quantum yield of electron transport is reduced from c. 0.6 to 0.2. Two-dimensional imaging analysis of the chlorophyll fluorescence signal revealed that the yield reduction spreads acropetally through the pinna and via the veins through the leaflets. • To determine the speed of a chemical signal, a part of a pinna was exposed to 14 CO2 . The remaining parts of the leaf were provided with label only when the translocation was extended to 12 h, indicating that a chemical signal is much too slow to account for the photosynthetic response after heat stimulation. • The results provide evidence for a role of the electrical signal in the regulation of photosynthesis because the high speed of the signal transduction rules out the involvement of a chemical signal, and the photosynthetic response occurs after the arrival of the electrical signal in the leaf pinna.
Keywords: Mimosa pudica; Photosystem II electron quantum yield; chlorophyll fluorescence imaging; electrical signals.