Participation of intracellular and extracellular pH changes in photosynthetic response development induced by variation potential in pumpkin seedlings.

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.

[Influence of a variation potential on photosynthesis in pumpkin seedlings (Cucurbita pepo L.)].

The influence of a variation potential on photosynthesis in pumpkin seedlings (Cucurbita pepo L.) was investigated in our work. It was shown that the variation potential induced by cotyledon burning propagates into a leaf. It decreases CO2 assimilation and transpiration as well as increases nonphotochemical quenching. Investigation of isolated chloroplasts showed that lowering of the pH in incubation medium from 6.9-7.2 to 6.5 increases nonphotochemical quenching. It was proposed that lowering of the cytoplasmic pH induced by the variation potential takes place in the photosynthetic response development.

[An extracellular pH changes registration by confocal microscopy in higher plant at the excitation potentials generation].

Confocal microscopy technique was applied for registration of apoplast pH changes in the Cucurbita pepo seedling stem during generation of action potential and variation potential. Fluorescent dye FITC-dextran was used for pH-changes registration. Analysis of fluorescence images and fluorescence spectra showed, that FITC-dextran was localized in cell walls. Propagation of action potential and variation potential was accompanied by transient increase of fluorescence intensity, which indicated alkalization of cell walls. This transient alkalization is proposed to be caused by a temporary inactivation of the H(+)-pump in the plasma membrane.

[Influence of propagating electrical signals on delayed luminescence of geranium leaves. II. Theoretical analysis].

A mathematical model of delayed luminescence was devised. It is based on the description of primary photosynthetic reactions, which takes the donor and acceptor parties of photosystem II and the electrochemical gradient on thylakoid membranes into account. The model was used for the theoretical analysis of the mechanisms of changes in delayed luminescence characteristics, induced by variation potentials.

[Influence of propagating electrical signals on delayed fluorescence of geranium leaves. 1. Experimental analysis].

It was shown that local damaging stimulation of geranium graft induced the generation and propagation of electrical signals (variation potential), which changed the parameters of delayed luminescence in the leaf blade. The responses of delayed luminescence included two stages, which probably occur by different mechanisms.