Electrical signals (action potential and variation potential, VP) caused by environmental stimuli are known to induce various physiological responses in plants, including changes in photosynthesis; however, their functional mechanisms remain unclear. In this study, the influence of VP on photosynthesis in pea (Pisum sativum L.) was investigated and the proton participation in this process analysed. VP, induced by local heating, inactivated photosynthesis and activated respiration, with the initiation of the photosynthetic response connected with inactivation of the photosynthetic dark stage; however, direct VP influence on the light stage was also probable. VP generation was accompanied with pH increases in apoplasts (0.17-0.30 pH unit) and decreases in cytoplasm (0.18-0.60 pH unit), which probably reflected H(+) -ATPase inactivation and H(+) influx during this electrical event. Imitation of H(+) influx using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) induced a photosynthetic response that was similar with a VP-induced response. Experiments on chloroplast suspensions showed that decreased external pH also induced an analogous response and that its magnitude depended on the magnitude of pH change. Thus, the present results showed that proton cellular influx was the probable mechanism of VP's influence on photosynthesis in pea. Potential means of action for this influence are discussed.

Cyclic electron flow is an important component of the total photosynthetic electron flow and participates in adaptation to the action of stressors. Local leaf stimulation induces electrical signals, including variation potential (VP), which inactivate photosynthesis; however, their influence on cyclic electron flow has not been investigated. The aim of this study was to investigate VP's influence on cyclic electron flow in pea (Pisum sativum L.). VP was induced in pea seedling leaves by local heating and measured in an adjacent, undamaged leaf by extracellular electrodes. CO2 assimilation was measured using a portable gas exchange measuring system. Photosystem I and II parameters were investigated using a measuring system for simultaneous assessment of P700 oxidation and chlorophyll fluorescence. Heating-induced VP reduced CO2 assimilation and electron flow through photosystem II. In response, cyclic electron flow rapidly decreased and subsequently slowly increased. Slow increases in cyclic flow were caused by decreased electron flow through photosystem II, which was mainly connected with VP-induced photosynthetic dark stage inactivation. However, direct influence by VP on photosystem I also participated in activation of cyclic electron flow. Thus, VP, induced by local leaf-heating, activated cyclic electron flow in undamaged leaves. This response was similar to photosynthetic changes observed under the direct action of stressors. Possible mechanisms of VP's influence on cyclic flow were discussed.

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Variation potential (VP), a propagating electrical signal unique to plants, induces a number of changes in many physiological processes. However, the mechanisms of its generation and propagation are still under discussion and require experimental and theoretical analysis, including VP simulations. The mathematical model for VP formation in plants has been worked out and is based on our previous description of electrophysiological processes in higher plant cells, including plasma membrane ion transport systems (K(+), Cl(-) and Ca(2+) channels, H(+) and Ca(2+)-ATPase, 2H(+)/Cl(-) symporter and H(+)/K(+) antiporter) and their regulation, ion concentration changes in cells and extracellular spaces and buffers in cytoplasm and apoplast. In addition, the VP model takes into account wound substance diffusion, which is described by a one-dimensional diffusion equation, and ligand-gated Ca(2+) channels, which are activated by this substance. The VP model simulates the experimental dependence of amplitude, velocity and shape of VP on the distance from the wounding site and describes the influence of metabolic inhibitors, divalent cation chelators and anion channel blockers on the generation of this electrical reaction, as shown in experiments. Thus, our model favorably simulates VP in plants and theoretically supports the role of wound substance diffusion and Ca(2+) influx in VP development.

Electrical signals presented in plants by action potential and by variation potential (VP) can induce a reversible inactivation of photosynthesis. Changes in the intracellular and extracellular pH during VP generation are a potential mechanism of photosynthetic response induction; however, this hypothesis requires additional experimental investigation. The purpose of the present work was to analyze the influence of pH changes on induction of the photosynthetic response in pumpkin. It was shown that a burning of the cotyledon induced VP propagation into true leaves of pumpkin seedlings inducing a decrease in the photosynthetic CO2 assimilation and an increase in non-photochemical quenching of fluorescence, whereas respiration was activated insignificantly. The photosynthetic response magnitude depended linearly on the VP amplitude. The intracellular and extracellular concentrations of protons were analyzed using pH-sensitive fluorescent probes, and the VP generation was shown to be accompanied by apoplast alkalization (0.4 pH unit) and cytoplasm acidification (0.3 pH unit). The influence of changes in the incubation medium pH on the non-photochemical quenching of fluorescence of isolated chloroplasts was also investigated. It was found that acidification of the medium stimulated the non-photochemical quenching, and the magnitude of this increase depended on the decrease in pH. Our results confirm the contribution of changes in intracellular and extracellular pH to induction of the photosynthetic response caused by VP. Possible mechanisms of the influence of pH changes on photosynthesis are discussed.

Variation potential (VP) in higher plants cells is a transitory depolarization of the plasma membrane occurring in response to external damage. The effects of VP on different physiological processes are actively studied, but little is known about their ionic nature, which limits the interpretation of VP-induced functional changes. It is thought that VP generation is based on transient inactivation of plasma membrane proton pumps and is not connected to passive ionic fluxes. To study burn-induced VP in wheat seedlings, we measured membrane electric potential and cell input resistance. Cell input resistance decreased during VP generation, indicating that ionic channels were activated. In addition, VP amplitude decreased when the extracellular calcium concentration was lowered. When anion channels were blocked by ethacrynic acid addition, the VP had poor depolarization speed and amplitude. A decrease in the chlorine gradient by extracellular chlorine concentration shift leads to lowering of the VP amplitude and depolarization speed. This result indicates the role of chlorine efflux in depolarization phase formation. The VP repolarization is connected to potassium ion efflux, that is confirmed by repolarization suppression under addition of the potassium channel blocker tetraethylammonium (TEA) and an increase in the extracellular potassium concentration. We also showed that the addition of a proton pump inhibitor leads to membrane potential depolarization and inhibition of VP generation. These results suggest that the VP may be formed not only by transient suppression of proton pumps but also by passive ionic fluxes through the membrane.

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The role of ions in the generation and mechanism of propagation of variation potential (VP) has been widely investigated. It is likely that Ca 2C influx via calcium channels is an initial stage of VP; however, development of longterm membrane depolarization requires prolonged open times of calcium channels. We investigated depolarization time in the present study. It was shown that local burning induced VP in wheat seedling and the electrical response was suppressed under EGTA presence. Depolarization formation, which may indicate open time of calcium channels at VP generation, was observed up to 30 s after reaction induction when calcium ions were added to initially calcium-free medium. Long-term calcium channel open time may be the reason for long membrane depolarization at VP and may also be connected with the type of channels participating in wound reaction propagation.