Changes in Activity of the Plasma Membrane H+-ATPase as a Link Between Formation of Electrical Signals and Induction of Photosynthetic Responses in Higher Plants

Action of numerous adverse environmental factors on higher plants is spatially-heterogenous; it means that induction of a systemic adaptive response requires generation and transmission of the stress signals. Electrical signals (ESs) induced by local action of stressors include action potential, variation potential, and system potential and they participate in formation of fast physiological changes at the level of a whole plant, including photosynthetic responses. Generation of these ESs is accompanied by the changes in activity of H+-ATPase, which is the main system of electrogenic proton transport across the plasma membrane. Literature data show that the changes in H+-ATPase activity and related changes in intra- and extracellular pH play a key role in the ES-induced inactivation of photosynthesis in non-irritated parts of plants. This inactivation is caused by both suppression of CO2 influx into mesophyll cells in leaves, which can be induced by the apoplast alkalization and, probably, cytoplasm acidification, and direct influence of acidification of stroma and lumen of chloroplasts on light and, probably, dark photosynthetic reactions. The ES-induced inactivation of photosynthesis results in the increasing tolerance of photosynthetic machinery to the action of adverse factors and probability of the plant survival.

Simulated Analysis of Influence of Changes in H+-ATPase Activity and Membrane CO2 Conductance on Parameters of Photosynthetic Assimilation in Leaves

Photosynthesis is an important process in plants which influences their development and productivity. Many factors can control the efficiency of photosynthesis, including CO₂ conductance of leaf mesophyll, which affects the CO₂ availability for Rubisco. It is known that electrical stress signals can decrease this conductance, and the response is probably caused by inactivation of H⁺-ATPase in the plasma membrane. In the current work, we analyzed the influence of both CO₂ conductance in the plasma membrane, and chloroplast envelopes and H⁺-ATPase activity on photosynthetic CO₂ assimilation, using a two-dimensional mathematical model of photosynthesis in leaves. The model included a description of assimilation on the basis of the Farquhar-von Caemmerer-Berry model, ion transport through the plasma membrane, diffusion of CO₂ in the apoplast, and transport of CO₂ through the plasma membrane and chloroplast envelope. The model showed that the photosynthetic CO₂ assimilation rate was mainly dependent on the plasma membrane and chloroplast envelope conductance; direct influence of the H⁺-ATPase activity (through changes in pH and CO₂/HCO₃^- concentration ratio) on this rate was weak. In contrast, both changes in CO₂ conductance of the plasma membrane and chloroplast envelopes and changes in the H⁺-ATPase activity influenced spatial heterogeneity of the CO₂ assimilation on the leaf surface in the simulated two-dimensional system. These effects were also observed under simultaneous changes in the CO₂ conductance of the plasma membrane and H⁺-ATPase activity. Qualitatively similar influence of changes in the CO₂ conductance of the plasma membrane and chloroplast envelopes, and changes in the H⁺-ATPase activity on photosynthesis were shown for two different densities of stomata in the simulated leaf; however, lowering the density of stomata decreased the assimilation rate and increased the heterogeneity of assimilation. The results of the model analysis clarify the potential influence of H⁺-ATPase inactivation on photosynthesis, and can be the basis for development of new methods for remote sensing of the influence of electrical signals.

Development of Two-Dimensional Model of Photosynthesis in Plant Leaves and Analysis of Induction of Spatial Heterogeneity of CO2 Assimilation Rate under Action of Excess Light and Drought

Photosynthesis is a key process in plants that can be strongly affected by the actions of environmental stressors. The stressor-induced photosynthetic responses are based on numerous and interacted processes that can restrict their experimental investigation. The development of mathematical models of photosynthetic processes is an important way of investigating these responses. Our work was devoted to the development of a two-dimensional model of photosynthesis in plant leaves that was based on the Farquhar-von Caemmerer-Berry model of CO₂ assimilation and descriptions of other processes including the stomatal and transmembrane CO₂ fluxes, lateral CO₂ and HCO₃^- fluxes, transmembrane and lateral transport of H⁺ and K⁺, interaction of these ions with buffers in the apoplast and cytoplasm, light-dependent regulation of H⁺-ATPase in the plasma membrane, etc. Verification of the model showed that the simulated light dependences of the CO₂ assimilation rate were similar to the experimental ones and dependences of the CO₂ assimilation rate of an average leaf CO₂ conductance were also similar to the experimental dependences. An analysis of the model showed that a spatial heterogeneity of the CO₂ assimilation rate on a leaf surface should be stimulated under an increase in light intensity and a decrease in the stomatal CO₂ conductance or quantity of the open stomata; this prediction was supported by the experimental verification. Results of the work can be the basis of the development of new methods of the remote sensing of the influence of abiotic stressors (at least, excess light and drought) on plants.

Electrical Signals, Plant Tolerance to Actions of Stressors, and Programmed Cell Death: Is Interaction Possible?

In environmental conditions, plants are affected by abiotic and biotic stressors which can be heterogenous. This means that the systemic plant adaptive responses on their actions require long-distance stress signals including electrical signals (ESs). ESs are based on transient changes in the activities of ion channels and H⁺-ATP-ase in the plasma membrane. They influence numerous physiological processes, including gene expression, phytohormone synthesis, photosynthesis, respiration, phloem mass flow, ATP content, and many others. It is considered that these changes increase plant tolerance to the action of stressors; the effect can be related to stimulation of damages of specific molecular structures. In this review, we hypothesize that programmed cell death (PCD) in plant cells can be interconnected with ESs. There are the following points supporting this hypothesis. (i) Propagation of ESs can be related to ROS waves; these waves are a probable mechanism of PCD initiation. (ii) ESs induce the inactivation of photosynthetic dark reactions and activation of respiration. Both responses can also produce ROS and, probably, induce PCD. (iii) ESs stimulate the synthesis of stress phytohormones (e.g., jasmonic acid, salicylic acid, and ethylene) which are known to contribute to the induction of PCD. (iv) Generation of ESs accompanies K⁺ efflux from the cytoplasm that is also a mechanism of induction of PCD. Our review argues for the possibility of PCD induction by electrical signals and shows some directions of future investigations in the field.

Inactivation of H+-ATPase Participates in the Influence of Variation Potential on Photosynthesis and Respiration in Peas

Local damage (e.g., burning, heating, or crushing) causes the generation and propagation of a variation potential (VP), which is a unique electrical signal in higher plants. A VP influences numerous physiological processes, with photosynthesis and respiration being important targets. VP generation is based on transient inactivation of H+-ATPase in plasma membrane. In this work, we investigated the participation of this inactivation in the development of VP-induced photosynthetic and respiratory responses. Two- to three-week-old pea seedlings (Pisum sativum L.) and their protoplasts were investigated. Photosynthesis and respiration in intact seedlings were measured using a GFS-3000 gas analyzer, Dual-PAM-100 Pulse-Amplitude-Modulation (PAM)-fluorometer, and a Dual-PAM gas-exchange Cuvette 3010-Dual. Electrical activity was measured using extracellular electrodes. The parameters of photosynthetic light reactions in protoplasts were measured using the Dual-PAM-100; photosynthesis- and respiration-related changes in O2 exchange rate were measured using an Oxygraph Plus System. We found that preliminary changes in the activity of H+-ATPase in the plasma membrane (its inactivation by sodium orthovanadate or activation by fusicoccin) influenced the amplitudes and magnitudes of VP-induced photosynthetic and respiratory responses in intact seedlings. Decreases in H+-ATPase activity (sodium orthovanadate treatment) induced fast decreases in photosynthetic activity and increases in respiration in protoplasts. Thus, our results support the effect of H+-ATPase inactivation on VP-induced photosynthetic and respiratory responses.

Exogenous Abscisic Acid Can Influence Photosynthetic Processes in Peas through a Decrease in Activity of H+-ATP-ase in the Plasma Membrane

Simple Summary

Numerous stressors (drought, low and high temperatures, mechanical damages, etc.) act on plants under environmental conditions, suppressing their physiological processes (in particular, photosynthesis). Abscisic acid (ABA) is an important hormone, which participates in increasing plant tolerance to the action of stressors; as a result, treatment by exogenous ABA is a perspective way of regulating the tolerance in agriculture. We investigated the influence of ABA spraying on photosynthetic processes, as well as on their heat tolerance and their regulation by electrical signals propagating after local burning and modifying photosynthesis. It was shown that ABA spraying decreased photosynthetic activity and increased photosynthetic heat tolerance; additionally, the ABA treatment weakened the influence of electrical signals on photosynthesis. We revealed that these responses could be caused by a decrease in activity of H⁺-ATP-ase, which is an important ion transporter in plant cell plasma membrane that supports efflux of H⁺ from cytoplasm. As a whole, our results show the potential influence of the ABA treatment on photosynthetic processes, which is related to a decrease in activity of H⁺-ATP-ase. The result can be potentially useful for development of new methods of management of plant tolerance in agriculture.

Abstract

Abscisic acid (ABA) is an important hormone in plants that participates in their acclimation to the action of stressors. Treatment by exogenous ABA and its synthetic analogs are a potential way of controlling the tolerance of agricultural plants; however, the mechanisms of influence of the ABA treatment on photosynthetic processes require further investigations. The aim of our work was to investigate the participation of inactivation of the plasma membrane H⁺-ATP-ase on the influence of ABA treatment on photosynthetic processes and their regulation by electrical signals in peas. The ABA treatment of seedlings was performed by spraying them with aqueous solutions (10⁻⁵ M). The combination of a Dual-PAM-100 PAM fluorometer and GFS-3000 infrared gas analyzer was used for photosynthetic measurements; the patch clamp system on the basis of a SliceScope Pro 2000 microscope was used for measurements of electrical activity. It was shown that the ABA treatment stimulated the cyclic electron flow around photosystem I and decreased the photosynthetic CO₂ assimilation, the amplitude of burning-induced electrical signals (variation potentials), and the magnitude of photosynthetic responses relating to these signals; in contrast, treatment with exogenous ABA increased the heat tolerance of photosynthesis. An investigation of the influence of ABA treatment on the metabolic component of the resting potential showed that this treatment decreased the activity of the H⁺-ATP-ase in the plasma membrane. Inhibitor analysis using sodium orthovanadate demonstrated that this decrease may be a mechanism of the ABA treatment-induced changes in photosynthetic processes, their heat tolerance, and regulation by electrical signals.

The electrical signal-induced systemic photosynthetic response is accompanied by changes in the photochemical reflectance index in pea

Plants can be affected by numerous environmental stressors with spatially heterogeneous actions on their bodies. A fast systemic photosynthetic response, which is connected with long-distance electrical signalling, plays an important role in the adaptation of higher plants to the action of stressors. Potentially, measurement of the response by using a photochemical reflectance index (PRI) could be the basis of monitoring photosynthesis under spatially heterogeneous stressors; however, the method has not been previously used for investigating the systemic photosynthetic response. We investigated changes in PRI and photosynthetic parameters (quantum yields of PSI and PSII and nonphotochemical quenching) in intact leaves of pea (Pisum sativum L.) after local heating of another leaf and the propagation of electrical signals through the plant body. We showed that electrical signals decreased the quantum yields of PSI and PSII and increased the nonphotochemical quenching of intact leaves in times ranging from minutes to tens of minutes; the changes were strongly connected with changes in PRI. Additional analysis showed that changes in PRI were caused by an increase of the energy-dependent quenching induced by electrical signals. Thus PRI can be potentially used for monitoring the systemic photosynthetic response connected with long-distance electrical signalling.

Long-distance electrical signals as a link between the local action of stressors and the systemic physiological responses in higher plants

Our review is devoted to the analysis of the role of long-distance electrical signals in the development of the fast systemic physiological responses in higher plants. The characteristics and mechanisms of basic electrical signals (variation potential, action potential and system potential) are analyzed, and a potential schema of the generation and propagation of the system potential is proposed. The review summarizes the physiological changes induced by the variation potential, action potential and system potential in higher plants, including changes in gene expressions, the production of phytohormones, photosynthesis, phloem mass-flow, respiration, ATP content, transpiration and plant growth. Potential mechanisms of the changes are analyzed. Finally, a hypothetical schema, which describes a hierarchy of the variation potential, action potential and system potential, in the development of the fast systemic non-specific adaptation of plants to stressors, is proposed.