Electrical signals (action and variation potentials)caused by environmental stimuli induce a number of physiological responses in plants including changes in photosynthesis; however, mechanisms of these changes remain unclear. We investigated the influence of the variation potential on photosynthesis in geranium (Pelargonium zonale) under different conditions (control, low external CO2 concentration, and actinic light absence). The variation potential caused by lamina burning induced a reduction in photosynthesis (decreases in effective quantum yields of photosystem I and II, CO2 assimilation rate, and stomatal conductance) in unstimulated leaves under control conditions. Changes in the majority of light-stage parameters (photosystem I and II quantum yields, coefficients of photochemical and non-photochemical quenching, quantum yield of non-photochemical energy dissipation in photosystem I due to donor-side limitation) were correlated with a decrease in CO2 assimilation rate. The changes were similar to those caused by lowering [CO2]; their magnitudes decreased both under low external CO2 concentration and without actinic light. These results support the hypothesis that Calvin cycle inactivation plays a key role in photosynthetic response induced by electrical signals. However, a decrease in electron transport through the PSI acceptor side also induced by variation potential was not correlated with a decrease in the CO2 assimilation rate and did not depend on the external CO2 concentration or actinic light intensity. Thus, we suggest that there are two different mechanisms of light-stage inactivation induced by the variation potential in geranium: one strongly dependent on dark-stage inactivation and one weakly dependent on dark-stage inactivation.
Planta. 2011. DOI 10.1007/s00425-011-1529-2. [Epub ahead of print]