Plants are constantly exposed to various stressors, including drought, fluctuations in temperature and light intensity, attacks by insects, etc. Since plants have an attached lifestyle, the only way to survive the impact of the stress factor is to quickly adapt their metabolism to the changing conditions. In the case when stressors (for example, strong light or mechanical damage) only act on certain parts of the plant organism, special stress signals propagate in the plant. One of the primary responses of the plant to local stressors is to generate and propagate electrical stress signals, in particular, the variation potential.
Variation potential is a unique electrical signal in plants arising in response to damaging effects that pose a potential threat to the plant's life. It is known that the variation potential can significantly reduce photosynthesis in plants, thereby increasing their resistance to stressors and, apparently, reducing their productivity. An important feature of the variation potential is the prolonged inactivation of ?+-ATPase in the biological membrane surrounding the cell. ?+-ATPase is a special membrane enzyme that uses ATP energy to pump hydrogen protons from the intracellular space to the extracellular space. As a consequence, a decrease in the activity of ?+-ATPase in the propagation of the variation potential should result in a rapid change in the intra- and extracellular pH. Earlier, researchers at the UNN Department of Biophysics supposed that these changes in pH underlie the decrease in photosynthesis caused by the variation potential. Currently, this hypothesis is being verified experimentally and theoretically.
The paper by Ekaterina Sukhova and her co-authors published in the latest issue of Photosynthesis Research presents the results of experimental study of photosynthesis regulation by electrical signals and the possible role of pH in this process.
According to Ekaterina Sukhova who is a graduate student of the Lobachevsky University Department of Biophysics, it was shown experimentally that the variation potential (VP) propagating across the plant caused intensification of light energy absorption by photosystem II, which is one of the key photosynthetic enzymes in chloroplasts.
"Apparently, the observed effect was associated with acidification of the chloroplast lumen, due to the inactivation of ?+-ATPase. It is important to note that this was accompanied not only by an increase in absorption, but also by an increase in the dissipation of light energy, which means that energy losses increased during the operation of the photosynthetic apparatus," Ekaterina Sukhova noted.
Another consequence of VP propagation and pH changes in the cytoplasm and chloroplasts of plant cells was a rapid and reversible increase in the flow of electrons through the chloroplast electron transport chain. Here, the initial increase in the electron flow was apparently associated with an increase in the absorption of the light energy by photosystem II. In turn, a slow decrease in the electron flow is associated with an increase in the thermal dissipation of photosynthetic energy and a decrease in the electron transfer activity between photosystem II and photosystem I, which is the second key photosynthetic enzyme. The latter process, apparently, is also a consequence of the pH decrease inside the chloroplasts.
The results obtained are of fundamental importance, since it was shown for the first time that variation potential can influence the absorption of light and the distribution of light energy in the photosynthetic apparatus, as well as the transfer of electrons between the photosystems. At the same time, these results have significant applied implications. Since intracellular signals play an important role in adapting plants to the effects of unfavorable factors, the ability to regulate them provides an additional tool for controlling the resistance of agricultural plants to such factors and increasing crop yields.