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

Analysis of the Mechanisms Underlying the Specificity of the Variation Potential Induced by Different Stimuli

Plants are able to perceive diverse environmental factors and form an appropriate systemic functional response. Systemic responses are induced by stimulus-specific long-distance signals that carry information about the stimulus. Variation potential is proposed as a candidate for the role of such a signal. Here, we focus on the mechanisms that determine the specificity of the variation potential under the action of different local stimuli. Local stimuli such as heating, burning and wounding cause variation potential, the parameters of which differ depending on the type of stimulus. It was found that the stimulus-specific features of the hydraulic signal monitored by changes in leaf thickness and variation potential, such as a greater amplitude upon heating and burning and a significant amplitude decrement upon burning and wounding, were similar. The main features of these signals are the greater amplitude upon heating and burning, and a significant amplitude decrement upon burning and wounding. Together with the temporal correspondence of signal propagation, this evidence indicates a role for the hydraulic signal in the induction of stimulus-specific variation potential. Experiments using mechanosensitive channel inhibitors have demonstrated that the hydraulic signal contributes more to the induction of the variation potential in the case of rapidly growing stimuli, such as burning and wounding, than in the case of gradual heating. For thermal stimuli (gradual heating and burning), a greater contribution, compared to wounding, of the chemical signal related to reactive oxygen species to the induction of the variation potential was demonstrated. Thus, the specificity of the parameters of the variation potential is determined by the different contributions of hydraulic and chemical signals.

Electrical Signaling Beyond Neurons

Neural action potentials (APs) are difficult to interpret as signal encoders and/or computational primitives. Their relationships with stimuli and behaviors are obscured by the staggering complexity of nervous systems themselves. We can reduce this complexity by observing that "simpler" neuron-less organisms also transduce stimuli into transient electrical pulses that affect their behaviors. Without a complicated nervous system, APs are often easier to understand as signal/response mechanisms. We review examples of nonneural stimulus transductions in domains of life largely neglected by theoretical neuroscience: bacteria, protozoans, plants, fungi, and neuron-less animals. We report properties of those electrical signals-for example, amplitudes, durations, ionic bases, refractory periods, and particularly their ecological purposes. We compare those properties with those of neurons to infer the tasks and selection pressures that neurons satisfy. Throughout the tree of life, nonneural stimulus transductions time behavioral responses to environmental changes. Nonneural organisms represent the presence or absence of a stimulus with the presence or absence of an electrical signal. Their transductions usually exhibit high sensitivity and specificity to a stimulus, but are often slow compared to neurons. Neurons appear to be sacrificing the specificity of their stimulus transductions for sensitivity and speed. We interpret cellular stimulus transductions as a cell's assertion that it detected something important at that moment in time. In particular, we consider neural APs as fast but noisy detection assertions. We infer that a principal goal of nervous systems is to detect extremely weak signals from noisy sensory spikes under enormous time pressure. We discuss neural computation proposals that address this goal by casting neurons as devices that implement online, analog, probabilistic computations with their membrane potentials. Those proposals imply a measurable relationship between afferent neural spiking statistics and efferent neural membrane electrophysiology.

pH change accompanying long-distance electrical signal controls systemic jasmonate biosynthesis

Local damaging stimuli cause a rapid increase in the content of the defense phytohormone jasmonic acid (JA) and its biologically active derivative jasmonoyl-L-isoleucine (JA-Ile) in undamaged distal tissues. The increase in JA and JA-Ile levels was coincident with a rapid decrease in the levels of the precursor 12-oxo-phytodienoic acid (OPDA). The propagation of a stimulus-induced long-distance electrical signal, variation potential (VP), which is accompanied by intracellular changes in pH and Ca2+ levels, preceded systemic changes in jasmonate content. The decrease in pH during VP, mediated by transient inactivation of the plasma membrane H+-ATPase, induced the conversion of OPDA to JA, probably by regulating the availability of the OPDA substrate to JA biosynthetic enzymes. The regulation of systemic synthesis of JA and JA-Ile by the Ca2+ wave accompanying VP most likely occurs by the same mechanism of pH-induced conversion of OPDA to JA due to Ca2+-mediated decrease in pH as a result of H+-ATPase inactivation. Thus, the transient increase in intracellular Ca2+ levels and the transient decrease in intracellular pH are most likely the key mechanisms of VP-mediated regulation of jasmonate production in systemic tissues upon local stimulation.

Local Action of Moderate Heating and Illumination Induces Electrical Signals, Suppresses Photosynthetic Light Reactions, and Increases Drought Tolerance in Wheat Plants

Local actions of stressors induce electrical signals (ESs), influencing photosynthetic processes and probably increasing tolerance to adverse factors in higher plants. However, the participation of well-known depolarization ESs (action potentials and variation potentials) in these responses seems to be rare under natural conditions, particularly in the case of variation potentials, which are induced by extreme stressors (e.g., burning). Earlier, we showed that the local action of moderate heating and illumination can induce low-amplitude hyperpolarization ESs influencing photosynthetic light reactions in wheat plants cultivated in a vegetation room. In the current work, we analyzed ESs and changes in photosynthetic light reactions and drought tolerance that were induced by a combination of moderate heating and illumination in wheat plants cultivated under open-ground conditions. It was shown that the local heating and illumination induced low-amplitude ESs, and the type of signal (depolarization or hyperpolarization) was dependent on distance from the irritated zone and wheat age. Induction of depolarization ESs was not accompanied by photosynthetic changes in plants under favorable conditions or under weak drought. In contrast, the changes were observed after induction of these signals under moderate drought. Increasing drought tolerance was also observed in the last case. Thus, low-amplitude ESs can participate in photosynthetic regulation and increase tolerance to drought in plants cultivated under open-ground conditions.

Green leaf volatile sensory calcium transduction in Arabidopsis

Plants perceive volatile organic compounds (VOCs) released by mechanically- or herbivore-damaged neighboring plants and induce various defense responses. Such interplant communication protects plants from environmental threats. However, the spatiotemporal dynamics of VOC sensory transduction in plants remain largely unknown. Using a wide-field real-time imaging method, we visualize an increase in cytosolic Ca2+ concentration ([Ca2+]cyt) in Arabidopsis leaves following exposure to VOCs emitted by injured plants. We identify two green leaf volatiles (GLVs), (Z)-3-hexenal (Z-3-HAL) and (E)-2-hexenal (E-2-HAL), which increase [Ca2+]cyt in Arabidopsis. These volatiles trigger the expression of biotic and abiotic stress-responsive genes in a Ca2+-dependent manner. Tissue-specific high-resolution Ca2+ imaging and stomatal mutant analysis reveal that [Ca2+]cyt increases instantly in guard cells and subsequently in mesophyll cells upon Z-3-HAL exposure. These results suggest that GLVs in the atmosphere are rapidly taken up by the inner tissues via stomata, leading to [Ca2+]cyt increases and subsequent defense responses in Arabidopsis leaves.

Ion Channels in Electrical Signaling in Higher Plants

Electrical signals (ESs) appearing in plants under the action of various external factors play an important role in adaptation to changing environmental conditions. Generation of ES in higher plant cells is associated with activation of Ca2+, K+, and anion fluxes, as well as with changes in the activity of plasma membrane H+-ATPase. In the present review, molecular nature of the ion channels contributing to ESs transmission in higher plants is analyzed based on comparison of the data from molecular-genetic and electrophysiological studies. Based on such characteristics of ion channels as selectivity, activation mechanism, and intracellular and tissue localization, those ion channels that meet the requirements for potential participation in ES generation were selected from a wide variety of ion channels in higher plants. Analysis of the data of experimental studies performed on mutants with suppressed or enhanced expression of a certain channel gene revealed those channels whose activation contributes to ESs formation. The channels responsible for Ca2+ flux during generation of ESs include channels of the GLR family, for K+ flux - GORK, for anions - MSL. Consideration of the prospects of further studies suggests the need to combine electrophysiological and genetic approaches along with analysis of ion concentrations in intact plants within a single study.

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.

Effect of low-dose ionizing radiation on spatiotemporal parameters of functional responses induced by electrical signals in tobacco plants

Plants growing under an increased radiation background may be exposed to additional stressors. Plant acclimatization is formed with the participation of stress signals that cause systemic responses-a change in the activity of physiological processes. In this work, we studied the mechanisms of the effect of ionizing radiation (IR) on the systemic functional responses induced by electrical signals. Chronic β-irradiation (31.3 μGy/h) have a positive effect on the morphometric parameters and photosynthetic activity of tobacco plants (Nicotiana tabacum L.) at rest. An additional stressor causes an electrical signal, which, when propagated, causes a temporary change in chlorophyll fluorescence parameters, reflecting a decrease in photosynthesis activity. Irradiation did not significantly affect the electrical signals. At the same time, more pronounced photosynthesis responses are observed in irradiated plants: both the amplitude and the leaf area covered by the reaction increase. The formation of such responses is associated with changes in pH and stomatal conductance, the role of which was analyzed under IR. Using tobacco plants expressing the fluorescent pH-sensitive protein Pt-GFP, it was shown that IR enhances signal-induced cytoplasmic acidification. It was noted that irradiation also disrupts the correlation between the amplitudes of the electrical signal, pH shifts, changes in chlorophyll fluorescence parameters. Also stronger inhibition of stomatal conductance by the signal was shown in irradiated plants. It was concluded that the effect of IR on the systemic response induced by the electrical signal is mainly due to its effect on the stage of signal transformation into the response.

Local Action of Increased Pressure Induces Hyperpolarization Electrical Signals and Influences Photosynthetic Light Reactions in Wheat Plants

Long-distance electrical signals caused by the local action of stressors influence numerous physiological processes in plants including photosynthesis and increase their tolerance to the action of adverse factors. Depolarization electrical signals were mainly investigated; however, we earlier showed that hyperpolarization electrical signals (HESs) can be caused by moderate stressors (e.g., local moderate heating) and induce photosynthetic inactivation. We hypothesized that HESs are related to stressor-induced increases in the hydrostatic pressure in the zone of action of the stressor and following the propagation of a hydraulic wave. In the current work, we tested this hypothesis through the direct investigation of electrical signals induced by the local action of artificially increased pressure and an analysis of the subsequent photosynthetic changes in the nonirritated parts of plants. The electrical signals and parameters of photosynthetic light reactions were investigated in wheat plants. The local action of the increased pressure was induced by the action of weights on the wheat leaf. Extracellular electrodes were used for electrical signal measurements. Pulse-amplitude-modulation fluorescent imaging was used for measurements of the quantum yield of photosystem II and nonphotochemical quenching of chlorophyll fluorescence in wheat leaves. It was shown that the local action of pressure on wheat leaf induced electrical signals near the irritated zone: HESs were caused by low pressure (10 kPa) and depolarization signals were induced by high pressure (100 kPa). The local action of moderate pressure (50 kPa) induced weak electrical signals near the irritated zone; however, HESs were observed with increasing distance from this zone. It was also shown that the local action of this moderate pressure induced the photosynthetic inactivation (decreasing the quantum yield of photosystem II and increasing the nonphotochemical quenching of chlorophyll fluorescence) in the nonirritated parts of the wheat leaves. Thus, our results show that the local action of the increased pressure and, probably, subsequent propagation of the hydraulic wave induce electrical signals (including HESs) and photosynthetic inactivation in nonirritated parts of plants that are similar to ones caused by the local action of moderate stressors (e.g., moderate heating). This means that both HESs and depolarization electrical signals can have a hydraulic mechanism of propagation.

Pea Aphid (Acyrthosiphon pisum) Host Races Reduce Heat-Induced Forisome Dispersion in Vicia faba and Trifolium pratense

Although phloem-feeding insects such as aphids can cause significant damage to plants, relatively little is known about early plant defenses against these insects. As a first line of defense, legumes can stop the phloem mass flow through a conformational change in phloem proteins known as forisomes in response to Ca²⁺ influx. However, specialized phloem-feeding insects might be able to suppress the conformational change of forisomes and thereby prevent sieve element occlusion. To investigate this possibility, we triggered forisome dispersion through application of a local heat stimulus to the leaf tips of pea (Pisum sativum), clover (Trifolium pratense) and broad bean (Vicia faba) plants infested with different pea aphid (Acyrthosiphon pisum) host races and monitored forisome responses. Pea aphids were able to suppress forisome dispersion, but this depended on the infesting aphid host race, the plant species, and the age of the plant. Differences in the ability of aphids to suppress forisome dispersion may be explained by differences in the composition and quantity of the aphid saliva injected into the plant. Various mechanisms of how pea aphids might suppress forisome dispersion are discussed.

Certain calcium channel inhibitors exhibit a number of secondary effects on the physiological properties in Nitellopsis obtusa: a voltage clamp approach

An unsolved problem of contemporary plant electrophysiology is the identity of Ca2+ channels responsible for the initiation of the action potential. We took a pharmacological approach and applied several Ca2+ channel blockers (verapamil, tetrandrine, and NED-19) on a Characean (Nitellopsis obtusa ) algae model system. The impact of the selected pharmaceuticals on the parameters of excitation transients of a single cell was analysed employing the two-electrode voltage clamp technique. It was revealed that tetrandrine exerted no effect, while both verapamil and NED-19 prolonged activation and inactivation durations of the excitatory Cl- current. NED-19 also significantly depolarised the excitation threshold membrane potential and shifted Ca2+ current reversal potential. Thus, NED-19 most specifically targeted Ca2+ channels. A viability assay paired with observations of cytoplasmic streaming revealed that verapamil affected not only Ca2+ channels but also exhibited non-specific effects, which eventually lead to cell death. Since many potential Ca2+ channel blockers exert additional undesirable non-specific effects, our study underlines the necessity to search for new more specific modulators of plant Ca2+ transport systems.

Systemic Signals Induced by Single and Combined Abiotic Stimuli in Common Bean Plants

To survive in a dynamic environment growing fixed to the ground, plants have developed mechanisms for monitoring and perceiving the environment. When a stimulus is perceived, a series of signals are induced and can propagate away from the stimulated site. Three distinct types of systemic signaling exist, i.e., (i) electrical, (ii) hydraulic, and (iii) chemical, which differ not only in their nature but also in their propagation speed. Naturally, plants suffer influences from two or more stimuli (biotic and/or abiotic). Stimuli combination can promote the activation of new signaling mechanisms that are explicitly activated, as well as the emergence of a new response. This study evaluated the behavior of electrical (electrome) and hydraulic signals after applying simple and combined stimuli in common bean plants. We used simple and mixed stimuli applications to identify biochemical responses and extract information from the electrical and hydraulic patterns. Time series analysis, comparing the conditions before and after the stimuli and the oxidative responses at local and systemic levels, detected changes in electrome and hydraulic signal profiles. Changes in electrome are different between types of stimulation, including their combination, and systemic changes in hydraulic and oxidative dynamics accompany these electrical signals.

The Effect of an Extremely Low-Frequency Electromagnetic Field on the Drought Sensitivity of Wheat Plants

Extremely low-frequency magnetic fields are thought to be capable of modulating the resistance of plants to adverse factors, particularly drought. Magnetic fields in this frequency range occur in nature in connection with so-called Schumann resonances, excited by lightning discharges in the Earth-ionosphere cavity. The aim of this work was to identify the influence of a magnetic field with a frequency of 14.3 Hz (which corresponds to the second Schumann harmonic) on the transpiration and photosynthesis of wheat plants under the influence of drought. The activity of photosynthesis processes, the crop water stress index, relative water content and leaf area were determined during drought intensification. At the end of the experiment, on the 12th day of drought, the length, and fresh and dry weight of wheat shoots were measured. The results obtained indicate a protective effect of the magnetic field on plants in unfavorable drought conditions; the magnetic field delayed the development of harmful changes in the transpiration and photosynthesis processes for several days. At the same time, in the absence of the stressor (drought), the effect of the electromagnetic field was not detected, except for a decrease in relative transpiration. In favorable conditions, there were only minimal modifications of the photosynthetic processes and transpiration by the magnetic field.

Integration of Electrical Signals and Phytohormones in the Control of Systemic Response

Plants are constantly exposed to environmental stresses. Local stimuli sensed by one part of a plant are translated into long-distance signals that can influence the activities in distant tissues. Changes in levels of phytohormones in distant parts of the plant occur in response to various local stimuli. The regulation of hormone levels can be mediated by long-distance electrical signals, which are also induced by local stimulation. We consider the crosstalk between electrical signals and phytohormones and identify interaction points, as well as provide insights into the integration nodes that involve changes in pH, Ca²⁺ and ROS levels. This review also provides an overview of our current knowledge of how electrical signals and hormones work together to induce a systemic response.

Summation of activation at the branch-stem transition of Mimosa pudica; a comparison with summation in cardiac tissue

In Mimosa pudica plants, local and global responses to environmental stimuli are associated with different types of electrical activity. Non-damaging stimuli (e.g. cooling) generate action potentials (APs), whereas damaging stimuli (e.g. heating) are associated with variation potentials (VPs). Local cooling of Mimosa branches resulted in APs that propagated up to the branch-stem interface and caused drooping of the branch (local response). This electrical activation did not pass the interface. If the branch was triggered by heat, however, a VP was transferred to the stem and caused activation of the entire plant (global response). VPs caused by heat were always preceded by APs and summation of the two types of activation appeared to be necessary for the activation to pass the branch-stem interface. Mechanical cutting of leaves also resulted in VPs preceded by APs, but in those cases a time delay was present between the two activations, which prevented adequate summation and transmission of activation. Simultaneous cold-induced activation of a branch and the stem below the interface occasionally resulted in summation sufficient to activate the stem beyond the interface. To investigate the effect of activation delay on summation, a similar structure of excitable converging pathways, consisting of a star-shaped pattern of neonatal rat heart cells, was used. In this model, summation of activation was not hindered by a small degree of asynchrony. The observations indicate that summation occurs in excitable branching structures and suggest that summation of activation plays a role in the propagation of nocuous stimuli in Mimosa.

Hyperpolarization electrical signals induced by local action of moderate heating influence photosynthetic light reactions in wheat plants

Local action of stressors induces fast changes in physiological processes in intact parts of plants including photosynthetic inactivation. This response is mediated by generation and propagation of depolarization electrical signals (action potentials and variation potentials) and participates in increasing plant tolerance to action of adverse factors. Earlier, we showed that a local action of physiological stimuli (moderate heating and blue light), which can be observed under environmental conditions, induces hyperpolarization electrical signals (system potentials) in wheat plants. It potentially means that these signals can play a key role in induction of fast physiological changes under the local action of environmental stressors. The current work was devoted to investigation of influence of hyperpolarization electrical signals induced by the local action of the moderate heating and blue light on parameters of photosynthetic light reactions. A quantum yield of photosystem II (Ф_PSII) and a non-photochemical quenching of chlorophyll fluorescence (NPQ) in wheat plants were investigated. It was shown that combination of the moderate heating (40°C) and blue light (540 µmol m^-2s^-1) decreased Ф_PSII and increased NPQ; these changes were observed in 3-5 cm from border of the irritated zone and dependent on intensity of actinic light. The moderate soil drought (7 days) increased magnitude of photosynthetic changes and shifted their localization which were observed on 5-7 cm from the irritated zone; in contrast, the strong soil drought (14 days) suppressed these changes. The local moderate heating decreased Ф_PSII and increased NPQ without action of the blue light; in contrast, the local blue light action without heating weakly influenced these parameters. It meant that just local heating was mechanism of induction of the photosynthetic changes. Finally, propagation of hyperpolarization electrical signals (system potentials) was necessary for decreasing Ф_PSII and increasing NPQ. Thus, our results show that hyperpolarization electrical signals induced by the local action of the moderate heating inactivates photosynthetic light reactions; this response is similar with photosynthetic changes induced by depolarization electrical signals. The soil drought and actinic light intensity can influence parameters of these photosynthetic changes.

Effect of extremely low-frequency magnetic fields on light-induced electric reactions in wheat

Magnetic field oscillations resulting from atmospheric events could have an effect on growth and development of plants and on the responsive reactions of plants to other environmental factors. In the current work, extremely low-frequency magnetic field (14.3 Hz) was shown to modulate light-induced electric reactions of wheat (Triticum aestivum L.). Blue light-induced electric reaction in wheat leaf comprises depolarization and two waves of hyperpolarization resulting in an increase of the potential to a higher level compared to the dark one. Fluorescent and inhibitory analysis demonstrate a key role of calcium ions and calcium-dependent H⁺-ATPase of the plasma membrane in the development of the reaction. Activation of H⁺-ATPase by the increased calcium influx is suggested as a mechanism of the influence of magnetic field on light-induced electric reaction.

Can electrophysiological information reflect the response of mangrove species to salt stress? A case study of rewatering and Sodium nitroprusside application

The changes in plant life behaviors and water status are accompanied by electrophysiological activities. In this study, the theoretical relationship between clamping force (C_F) and leaf resistance (R), capacitive reactance (X_C), inductive reactance (XL), impedance (Z), and capacitance (C) were exposed as 3-parameter exponential decay and linear models based on bioenergetics, respectively, for mangrove species. The intracellular water metabolism parameters and salt transport characteristics were also determined based on mechanical equations with influences of Sodium nitroprusside (SNP) and rewatering (R_W). The results show that the inherent capacitance and effective thickness could better represent Aegiceras corniculatum (A. corniculatum) species, and inherent resistance and impedance show obvious effects on Kandelia obovate (K. obovate) species at different salt levels. SNP application shows positive effect on different salt-resistance capacities of A. corniculatum, while K. obovate perform better in R_W phase at high salt level. These outcomes indicates that K. obovate is more salt-resistant because R_W process is consistent with actual situation, and response of A. corniculatum at high salt stress is irreversible, even in R_W. It is concluded that the electrophysiological parameters could be used for the determination of salt-resistant capacities, which gave more enhanced and reliable information of mangroves' life activities.

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.

Carbon supply and water status regulate fatty acid and triacylglycerol biosynthesis at transcriptional level in the olive mesocarp

The relative contribution of carbon sources generated from leaves and fruits photosynthesis for triacylglycerol biosynthesis in the olive mesocarp and their interaction with water stress was investigated. With this aim, altered carbon source treatments were combined with different irrigation conditions. A higher decrease in mesocarp oil content was observed in fruits under girdled and defoliated shoot treatment compared to darkened fruit conditions, indicating that both leaf and fruit photosynthesis participate in carbon supply for oil biosynthesis being leaves the main source. The carbon supply and water status affected oil synthesis in the mesocarp, regulating the expression of DGAT and PDAT genes and implicating DGAT1-1, DGAT2, PDAT1-1, and PDAT1-2 as the principal genes responsible for triacylglycerol biosynthesis. A major role was indicated for DGAT2 and PDAT1-2 in well-watered conditions. Moreover, polyunsaturated fatty acid content together with FAD2-1, FAD2-2 and FAD7-1 expression levels were augmented in response to modified carbon supply in the olive mesocarp. Furthermore, water stress caused an increase in DGAT1-1, DGAT1-2, PDAT1-1, and FAD2-5 gene transcript levels. Overall, these data indicate that oil content and fatty acid composition in olive fruit mesocarp are regulated by carbon supply and water status, affecting the transcription of key genes in both metabolic pathways.

Encoding, transmission, decoding, and specificity of calcium signals in plants

Calcium acts as a signal and transmits information in all eukaryotes. Encoding machinery consisting of calcium channels, stores, buffers, and pumps can generate a variety of calcium transients in response to external stimuli, thus shaping the calcium signature. Mechanisms for the transmission of calcium signals have been described, and a large repertoire of calcium binding proteins exist that can decode calcium signatures into specific responses. Whilst straightforward as a concept, mysteries remain as to exactly how such information processing is biochemically implemented. Novel developments in imaging technology and genetically encoded sensors (such as calcium indicators), in particular for multi-signal detection, are delivering exciting new insights into intra- and intercellular calcium signaling. Here, we review recent advances in characterizing the encoding, transmission, and decoding mechanisms, with a focus on long-distance calcium signaling. We present technological advances and computational frameworks for studying the specificity of calcium signaling, highlight current gaps in our understanding and propose techniques and approaches for unravelling the underlying mechanisms.

Effects of NaHSO3 on Cellular Metabolic Energy, Photosynthesis and Growth of Iris pseudacorus L

According to the law of energy conservation, the energy consumed by plants to resist adversity is equal to the difference between photosynthetic energy and growth energy consumption and cellular metabolic energy in plants. The cellular metabolic energy is calculated based on the electrical signals in plants. This study mainly investigated the effect of NaHSO3 on the growth and energy traits of the aquatic plant Iris pseudacorus L. and explored the effect of NaHSO3 on energy consumption in the process of plant development. In this study, NaHSO3 was used for simulating sulfur pollution in water medium. During the 20-day experiment period, the response of I. pseudocorus to the polluted water sources simulated by adding different concentrations of NaHSO3 (0, 0.5, 2, 4, 10 mmol·L−1) was monitored, and the internal mechanism of the relationship between the forms of energy and the removal of sulfur pollution was analyzed. After the 20-day exposure experiment, the growth and nutrient absorption capacity were significantly inhibited, and this inhibition proved to be concentration-dependent. In addition, high concentrations (4 and 10 mmol·L−1) of NaHSO3 might affect photosynthesis by disrupting cell membrane systems as it may interfere with membrane proteins and lipids and thus alter membrane integrity. Therefore, the cellular metabolic energy was increased and the sulfur absorption by I. pseudocorus was promoted under the low concentration (0.5 mmol/L−1) compared with the control, the role of NaHSO3 in promoting the growth of I. pseudocorus is much greater than its toxic effect under low concentrations. Under the hydroponic culture which contained 0.5 mmol·L−1 of NaHSO3, I. pseudocorus grew well and absorbed more sulfur. The results can be used as a reference for the cultivation of aquatic plants dealing with sulfur pollution, and dilution strategy can be set up to treat water medium that is seriously polluted with sulfur.

Influence of Burning-Induced Electrical Signals on Photosynthesis in Pea Can Be Modified by Soil Water Shortage

Local damage to plants can induce fast systemic physiological changes through generation and propagation of electrical signals. It is known that electrical signals influence numerous physiological processes including photosynthesis; an increased plant tolerance to actions of stressors is a result of these changes. It is probable that parameters of electrical signals and fast physiological changes induced by these signals can be modified by the long-term actions of stressors; however, this question has been little investigated. Our work was devoted to the investigation of the parameters of burning-induced electrical signals and their influence on photosynthesis under soil water shortage in pea seedlings. We showed that soil water shortage decreased the amplitudes of the burning-induced depolarization signals (variation potential) and the magnitudes of photosynthetic inactivation (decreasing photosynthetic CO₂ assimilation and linear electron flow and increasing non-photochemical quenching of the chlorophyll fluorescence and cyclic electron flow around photosystem I) caused by these signals. Moreover, burning-induced hyperpolarization signals (maybe, system potentials) and increased photosynthetic CO₂ assimilation could be observed under strong water shortage. It was shown that the electrical signal-induced increase of the leaf stomatal conductance was a potential mechanism for the burning-induced activation of photosynthetic CO₂ assimilation under strong water shortage; this mechanism was not crucial for photosynthetic response under control conditions or weak water shortage. Thus, our results show that soil water shortage can strongly modify damage-induced electrical signals and fast physiological responses induced by these signals.

Effect of Photoconversion Coatings for Greenhouses on Electrical Signal-Induced Resistance to Heat Stress of Tomato Plants

The use of photoconversion coatings is a promising approach to improving the quality of light when growing plants in greenhouses in low light conditions. In this work, we studied the effect of fluoropolymer coatings, which produce photoconversion of UV-A radiation and violet light into blue and red light, on the growth and resistance to heat stress of tomato plants (Solanum lycopersicum L.). The stimulating effect of the spectrum obtained as a result of photoconversion on plant growth and the activity of the photosynthesis process are shown. At the same time, the ability to withstand heat stress is reduced in plants grown under a photoconversion coating. Stress electrical signals, which normally increase resistance, in such plants have a much weaker protective effect on the photosynthetic apparatus. The observed effects are apparently explained by a decrease in the concentration of H₂O₂ in plants grown using photoconversion technologies, which leads to a shift in the development program towards increased productivity to the detriment of the protective function. Thus, when using photoconversion technologies in agricultural practice, it is necessary to pay increased attention to maintaining stable conditions during plant cultivation.

Ratio of Intensities of Blue and Red Light at Cultivation Influences Photosynthetic Light Reactions, Respiration, Growth, and Reflectance Indices in Lettuce

LED illumination can have a narrow spectral band; its intensity and time regime are regulated within a wide range. These characteristics are the potential basis for the use of a combination of LEDs for plant cultivation because light is the energy source that is used by plants as well as the regulator of photosynthesis, and the regulator of other physiological processes (e.g., plant development), and can cause plant damage under certain stress conditions. As a result, analyzing the influence of light spectra on physiological and growth characteristics during cultivation of different plant species is an important problem. In the present work, we investigated the influence of two variants of LED illumination (red light at an increased intensity, the "red" variant, and blue light at an increased intensity, the "blue" variant) on the parameters of photosynthetic dark and light reactions, respiration rate, leaf reflectance indices, and biomass, among other factors in lettuce (Lactuca sativa L.). The same light intensity (about 180 µmol m-2s-1) was used in both variants. It was shown that the blue illumination variant increased the dark respiration rate (35-130%) and cyclic electron flow around photosystem I (18-26% at the maximal intensity of the actinic light) in comparison to the red variant; the effects were dependent on the duration of cultivation. In contrast, the blue variant decreased the rate of the photosynthetic linear electron flow (13-26%) and various plant growth parameters, such as final biomass (about 40%). Some reflectance indices (e.g., the Zarco-Tejada and Miller Index, an index that is related to the core sizes and light-harvesting complex of photosystem I), were also strongly dependent on the illumination variant. Thus, our results show that the red illumination variant contributes a great deal to lettuce growth; in contrast, the blue variant contributes to stress changes, including the activation of cyclic electron flow around photosystem I.

Melatonin improves the photosynthesis in Dracocephalum kotschyi under salinity stress in a Ca2+/CaM-dependent manner

This study investigated: (1) the effects of various concentrations of melatonin (MT) and Ca2+; and (2) the impact of crosstalk between these signal molecules on photosynthesis and salt tolerance of Dracocephalum kotschyi Boiss. Results indicated that 5mM CaCl2, as well as 100μM MT were the best concentrations for increasing shoot dry weight, leaf area, SPAD index, maximum quantum efficiency of photosystem II (Fv/Fm), and decreasing malondialdehyde content under salinity stress. The impact of MT on growth and photosynthesis was closely linked to its effect on enhancing antioxidant enzyme activities in leaves. Application of p-chlorophenylalanine, as an inhibitor of MT biosynthesis, negated the impacts of MT on the aforementioned attributes. Salinity and MT boosted cytosolic Ca2+ concentration. Exogenous MT, as well as Ca2+, enhanced tolerance index, membrane stability, leaf area, the content of chlorophyll (Chl) a, Chl b, and carotenoids (Car), Fv/Fm, and stomatal conductance under salinity stress. These impacts of MT were eliminated by applying a calmodulin antagonist, a Ca2+ chelator and a Ca2+ channel blocker. These novel findings indicate that the MT-induced effects on photosynthetic parameters and salt-evoked oxidative stress were mediated through calcium/calmodulin (Ca2+/CaM) signalling.

A comparative study on the circadian rhythm of the electrical signals of Broussonetia papyrifera and Morus alba

The circadian clock regulates a wide range of physiological processes in plants. Here we showed the circadian variations of the electrical signals in Broussonetia papyrifera L. and Morus alba L. in a natural state, which were analyzed using the day-night cycle method. The circadian characteristics of different plant electrical signals were compared by constructing a coupling model for the circadian rhythm of plant electrical signals. The electrical signal sensor had two electrode plates, which were fixed on the two ends of the splint, leaves could then be clamped and measured. The clamping force between the two electrode plates was uniform, which enabled continuous and nondestructive measurements. The results showed that an electric cyclic behavior was observed (circadian cycle) with the circadian variation in the plants within 24 h. Both the resistance (R) and the impedance (Z) increased firstly in the early morning and then decreased subsequently, while the capacitance (C) showed an opposite variation. Under different weather conditions, plant electrical signals showed periodic changes when the temperature and light intensity in the environment slightly changed within the physiological tolerance of plant. This indicated that the circadian clock of plant electrical signals could be maintained endogenously. The variation curves of plant electrical signals as time increased were fitted using the sine equation. The characteristic parameters of circadian rhythm of plant electrical signals were obtained. We found that although all plant electrical signals exhibited electric cyclic behavior, but the characteristics of circadian rhythms of electrical signals were different. This study provided a scientific basic for precisely monitoring plant electrical signals, and a reference for revealing circadian rhythms of plant electrical signals and their occurrence rules.

Stem bending generates electrical response in poplar

Under natural conditions, plants experience external mechanical stresses such as wind and touch that impact their growth. A remarkable feature of this mechanically induced growth response is that it may occur at a distance from the stimulation site, suggesting the existence of a signal propagating through the plant. In this study, we investigated the electrical response of poplar trees to a transient controlled bending stimulation of the stem that mimics the mechanical effect of wind. Stem bending was found to cause an electrical response that we called "gradual" potential, similar in shape to an action potential. However, this signal can be distinguished from the well-known plant action potential by its propagation up to 20 cm along the stem and its strong dumping in velocity and amplitude. Two hypotheses regarding the mode of propagation of the "gradual" potential are discussed.

Broadening the definition of a nervous system to better understand the evolution of plants and animals

Most textbook definitions recognize only animals as having nervous systems. However, for the past couple decades, botanists have been meticulously studying long-distance signaling systems in plants, and some researchers have stated that plants have a simple nervous system. Thus, an academic conflict has emerged between those who defend and those who deny the existence of a nervous system in plants. This article analyses that debate, and we propose an alternative to answering yes or no: broadening the definition of a nervous system to include plants. We claim that a definition broader than the current one, which is based only on a phylogenetic viewpoint, would be helpful in obtaining a deeper understanding of how evolution has driven the features of signal generation, transmission and processing in multicellular beings. Also, we propose two possible definitions and exemplify how broader a definition allows for new viewpoints on the evolution of plants, animals and the nervous system.

Electrical Signaling of Plants under Abiotic Stressors: Transmission of Stimulus-Specific Information

Plants have developed complex systems of perception and signaling to adapt to changing environmental conditions. Electrical signaling is one of the most promising candidates for the regulatory mechanisms of the systemic functional response under the local action of various stimuli. Long-distance electrical signals of plants, such as action potential (AP), variation potential (VP), and systemic potential (SP), show specificities to types of inducing stimuli. The systemic response induced by a long-distance electrical signal, representing a change in the activity of a complex of molecular-physiological processes, includes a nonspecific component and a stimulus-specific component. This review discusses possible mechanisms for transmitting information about the nature of the stimulus and the formation of a specific systemic response with the participation of electrical signals induced by various abiotic factors.

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.

Stochastic Spatial Heterogeneity in Activities of H+-ATP-Ases in Electrically Connected Plant Cells Decreases Threshold for Cooling-Induced Electrical Responses

H⁺-ATP-ases, which support proton efflux through the plasma membrane, are key molecular transporters for electrogenesis in cells of higher plants. Initial activities of the transporters can influence the thresholds of generation of electrical responses induced by stressors and modify other parameters of these responses. Previously, it was theoretically shown that the stochastic heterogeneity of individual cell thresholds for electrical responses in a system of electrically connected neuronal cells can decrease the total threshold of the system (“diversity-induced resonance”, DIR). In the current work, we tested a hypothesis about decreasing the thresholds of generation of cooling-induced electrical responses in a system of electrically connected plant cells with increasing stochastic spatial heterogeny in the initial activities of H⁺-ATP-ases in these cells. A two-dimensional model of the system of electrically connected excitable cells (simple imitation of plant leaf), which was based on a model previously developed in our works, was used for the present investigation. Simulation showed that increasing dispersion in the distribution of initial activities of H⁺-ATP-ases between cells decreased the thresholds of generation of cooling-induced electrical responses. In addition, the increasing weakly influenced the amplitudes of electrical responses. Additional analysis showed two different mechanisms of the revealed effect. The increasing spatial heterogeneity in activities of H⁺-ATP-ases induced a weak positive shift of the membrane potential at rest. The shift decreased the threshold of electrical response generation. However, the decreased threshold induced by increasing the H⁺-ATP-ase activity heterogeneity was also observed after the elimination of the positive shift. The result showed that the “DIR-like” mechanism also participated in the revealed effect. Finally, we showed that the standard deviation of the membrane potentials before the induction of action potentials could be used for the estimation of thresholds of cooling-induced plant electrical responses. Thus, spatial heterogeneity in the initial activities of H⁺-ATP-ases can be a new regulatory mechanism influencing the generation of electrical responses in plants under actions of stressors.

Plant's electrophysiological information manifests the composition and nutrient transport characteristics of membrane proteins

Almost all life activities of plants are accompanied by electrophysiological information. Plant's electrical parameters are considered to be the fastest response to environment. In this study, the theoretically intrinsic relationships between the clamping force and leaf resistance (R) and inductive reactance (XL) were revealed as 3-parameter exponential decay based on bioenergetics for the first time. The intrinsic resistance (IR), capacitive reactance (IXc), inductive reactance (IXL), impedance (IZ), and capacitance (IC) in plant leaves were successfully monitored. The nutrient flux per unit area (UNF), nutrient transfer rate (NTR) and nutrient transport capacity (NTC) in plants based on IR, IXc, IXL, IZ and IC were defined to reflect nutrient transport characteristics. The results indicate that IXc and IXL could be used to manifest the relative composition characteristics of cell membrane proteins, and are inversely proportional to the amount of surface and binding proteins that induce membrane Xc and XL in plant leaves, respectively. UNF, NTR or NTC exhibited good correlations with crude protein or crude ash, and accurately revealed the nutrient transport strategies of tested plants and their diversity. This study highlights that plant's electrophysiological information could effectively manifest the composition and nutrient transport characteristics of membrane proteins in plant cells.

Plant electrical signals: A multidisciplinary challenge

Plant electrical signals, an early event in the plant-stimulus interaction, rapidly transmit information generated by the stimulus to other organs, and even the whole plant, to promote the corresponding response and trigger a regulatory cascade. In recent years, many promising state-of-the-art technologies applicable to study plant electrophysiology have emerged. Research focused on expression of genes associated with electrical signals has also proliferated. We propose that it is appropriate for plant electrical signals to be considered in the form of a "plant electrophysiological phenotype". This review synthesizes research on plant electrical signals from a novel, interdisciplinary perspective, which is needed to improve the efficient aggregation and use of plant electrical signal data and to expedite interpretation of plant electrical signals.

Understanding Plant Behavior: A Student Perspective

Biology students need special incentive to learn plant physiology. Framing plant function as 'behavior' analogous to animal neurobiology and behavior and integrating active learning methods is a successful way to generate an inclusive space for a wide range of learning styles, cultural backgrounds, and scientific contributions.

Influence of Local Burning on Difference Reflectance Indices Based on 400-700 nm Wavelengths in Leaves of Pea Seedlings

Local damage (e.g., burning) induces a variation potential (VP), which is an important electrical signal in higher plants. A VP propagates into undamaged parts of the plant and influences numerous physiological processes, including photosynthesis. Rapidly increasing plant tolerance to stressors is likely to be a result of the physiological changes. Thus, developing methods of revealing VP-induced physiological changes can be used for the remote sensing of plant systemic responses to local damage. Previously, we showed that burning-induced VP influenced a photochemical reflectance index in pea leaves, but the influence of the electrical signals on other reflectance indices was not investigated. In this study, we performed a complex analysis of the influence of VP induction by local burning on difference reflectance indices based on 400–700 nm wavelengths in leaves of pea seedlings. Heat maps of the significance of local burning-induced changes in the reflectance indices and their correlations with photosynthetic parameters were constructed. Large spectral regions with significant changes in these indices after VP induction were revealed. Most changes were strongly correlated to photosynthetic parameters. Some indices, which can be potentially effective for revealing local burning-induced photosynthetic changes, are separately shown. Our results show that difference reflectance indices based on 400–700 nm wavelengths can potentially be used for the remote sensing of plant systemic responses induced by local damages and subsequent propagation of VPs.

Participation of calcium ions in induction of respiratory response caused by variation potential in pea seedlings

Electrical signals in plants caused by external stimuli are capable of inducing various physiological responses. The mechanisms of transformation of a long-distance electrical signal (ES) into a functional response remain largely unexplored and require additional research. In this work, we investigated the role of calcium ions in the development of ES-induced respiratory response. Gradual heating of the leaf causes the propagation of variation potential (VP) in the pea seedling. The propagation of VP leads to a transient activation of respiration in an unaffected leaf. During the VP generation, a transient increase in the intracellular calcium concentration takes place. A calcium channel blocker inhibits the respiratory response, and a calcium ionophore induces the activation of respiration. Inhibitory analysis has showed that the VP-induced increase in respiration activity is probably associated with calcium-mediated activation of rotenone-insensitive alternative NADPH dehydrogenases in mitochondria.

Friends, neighbours and enemies: an overview of the communal and social biology of plants

Plants were traditionally seen as rather passive actors in their environment, interacting with each other only in so far as they competed for the same resources. In the last 30 years, this view has been spectacularly overturned, with a wealth of evidence showing that plants actively detect and respond to their neighbours. Moreover, there is evidence that these responses depend on the identity of the neighbour, and that plants may cooperate with their kin, displaying social behaviour as complex as that observed in animals. These plant-plant interactions play a vital role in shaping natural ecosystems, and are also very important in determining agricultural productivity. However, in terms of mechanistic understanding, we have only just begun to scratch the surface, and many aspects of plant-plant interactions remain poorly understood. In this review, we aim to provide an overview of the field of plant-plant interactions, covering the communal interactions of plants with their neighbours as well as the social behaviour of plants towards their kin, and the consequences of these interactions. We particularly focus on the mechanisms that underpin neighbour detection and response, highlighting both progress and gaps in our understanding of these fascinating but previously overlooked interactions.

Excitability and propagation of the electrical impulse in Venus flytrap; a comparative electrophysiological study of unipolar electrograms with myocardial tissue

Mammalian heart cells and cells of leaves of Dionaea muscipula share the ability to generate propagated action potentials, because the excitable cells are electrically coupled. In the heart the propagated action potential causes synchronized contraction of the heart muscle after automatic generation of the impulse in the sinus node. In Dionaea propagation results in closure of the trap after activation of trigger hairs by an insect. The electrical activity can be recorded in the extracellular space as an extracellular electrogram, resulting from transmembrane currents. Although the underlying physiological mechanism that causes the electrogram is similar for heart and Dionaea cells, the contribution of the various ions to the transmembrane current is different. We recorded extracellular electrograms from Dionaea leaves and compared the recorded signals with those known from the heart. The morphology of the electrograms differed considerably. In comparison to activation in mammalian myocardium, electrograms of Dionaea are more temporally and spatially variable. Whereas electrograms in healthy myocardium recorded at some distance from the site of activation reveal a simple biphasic pattern, Dionaea activation showed positive, negative or biphasic deflections. Comparison of patch clamp data from plant cells and cardiomyocytes suggests a role of temperature and ion concentrations in extracellular space for the diversity of morphologies of the Dionaea electrograms.

Impact of Mammalian Two-Pore Channel Inhibitors on Long-Distance Electrical Signals in the Characean Macroalga Nitellopsis obtusa and the Early Terrestrial Liverwort Marchantia polymorpha

Inhibitors of human two-pore channels (TPC1 and TPC2), i.e., verapamil, tetrandrine, and NED-19, are promising medicines used in treatment of serious diseases. In the present study, the impact of these substances on action potentials (APs) and vacuolar channel activity was examined in the aquatic characean algae Nitellopsis obtusa and in the terrestrial liverwort Marchantia polymorpha. In both plant species, verapamil (20-300 µM) caused reduction of AP amplitudes, indicating impaired Ca²⁺ transport. In N. obtusa, it depolarized the AP excitation threshold and resting potential and prolonged AP duration. In isolated vacuoles of M. polymorpha, verapamil caused a reduction of the open probability of slow vacuolar SV/TPC channels but had almost no effect on K⁺ channels in the tonoplast of N. obtusa. In both species, tetrandrine (20-100 µM) evoked a pleiotropic effect: reduction of resting potential and AP amplitudes and prolongation of AP repolarization phases, especially in M. polymorpha, but it did not alter vacuolar SV/TPC activity. NED-19 (75 µM) caused both specific and unspecific effects on N. obtusa APs. In M. polymorpha, NED-19 increased the duration of repolarization. However, no inhibition of SV/TPC channels was observed in Marchantia vacuoles, but an increase in open probability and channel flickering. The results indicate an effect on Ca²⁺ -permeable channels governing plant excitation.

Mechanisms of specific systemic response in wheat plants under different locally acting heat stimuli

Mechanisms of the specific systemic response of plant to different adverse factors are poorly understood. We studied the mechanisms acting in wheat (Triticum aestivum L.) under the action of local burn and gradual heating. Both stimuli induce a variation potential (VP) propagation and a biphasic (fast and long-term phases) photosynthetic response in non-stimulated zones of plant with stimulus-specific parameters of the latter: the fast phase or long-term phase predominance in responses induced by burn or heating, respectively. The burn-induced VP and photosynthetic response attenuate with distance, while the heating-induced VP and photosynthetic response were of more stable amplitude in distant part of the stimulated plant. VP propagation in both cases induced apoplast alkalization with dynamics well corresponding to such of VP and of the fast phase of photosynthetic response. Gradual heating induced a significant rise in jasmonate production along with a decrease in stomatal conductance with characteristic times well corresponding to the long-term phase of the photosynthetic response. We suppose that the VP-induced pH shift is responsible for in the induction of the fast phase, while jasmonate production for the long-term phase of the photosynthetic response. The revealed differences in the systemic response to stressors studied, apparently, reflect two distinct plant adaptation strategies to fast and slow-growing stimuli. The immediate response in the tissue nearest to the damage zone is the most important under a fast-growing stimulus. The fundamentally different situation is under a slowly-growing stimulus which provokes long-term changes in the plant that ensure the preparation of the whole organism for impending environmental changes.

A Theoretical Analysis of Relations between Pressure Changes along Xylem Vessels and Propagation of Variation Potential in Higher Plants

Variation potential (VP) is an important long-distance electrical signal in higher plants that is induced by local damages, influences numerous physiological processes, and participates in plant adaptation to stressors. The transmission of increased hydraulic pressure through xylem vessels is the probable mechanism of VP propagation in plants; however, the rates of the pressure transmission and VP propagation can strongly vary. We analyzed this problem on the basis of a simple mathematical model of the pressure distribution along a xylem vessel, which was approximated by a tube with a pressure gradient. It is assumed that the VP is initiated if the integral over pressure is more than a threshold one, taking into account that the pressure is transiently increased in the initial point of the tube and is kept constant in the terminal point. It was shown that this simple model can well describe the parameters of VP propagation in higher plants, including the increase in time before VP initiation and the decrease in the rate of VP propagation with an increase in the distance from the zone of damage. Considering three types of the pressure dynamics, our model predicts that the velocity of VP propagation can be stimulated by an increase in the length of a plant shoot and also depends on pressure dynamics in the damaged zone. Our results theoretically support the hypothesis about the impact of pressure variations in xylem vessels on VP propagation.

Influence of Magnetic Field with Schumann Resonance Frequencies on Photosynthetic Light Reactions in Wheat and Pea

Photosynthesis is an important target of action of numerous environmental factors; in particular, stressors can strongly affect photosynthetic light reactions. Considering relations of photosynthetic light reactions to electron and proton transport, it can be supposed that extremely low frequency magnetic field (ELFMF) may influence these reactions; however, this problem has been weakly investigated. In this paper, we experimentally tested a hypothesis about the potential influence of ELFMF of 18 µT intensity with Schumann resonance frequencies (7.8, 14.3, and 20.8 Hz) on photosynthetic light reactions in wheat and pea seedlings. It was shown that ELFMF decreased non-photochemical quenching in wheat and weakly influenced quantum yield of photosystem II at short-term treatment; in contrast, the changes in potential and effective quantum yields of photosystem II were observed mainly under chronic action of ELFMF. It is interesting that both short-term and chronic treatment decreased the time periods for 50% activation of quantum yield and non-photochemical quenching under illumination. Influence of ELFMF on pea was not observed at both short-term and chronic treatment. Thus, we showed that ELFMF with Schumann resonance frequencies could influence photosynthetic light processes; however, this effect depends on plant species (wheat or pea) and type of treatment (short-term or chronic).

Species-Specific and Distance-Dependent Dispersive Behaviour of Forisomes in Different Legume Species

Forisomes are giant fusiform protein complexes composed of sieve element occlusion (SEO) protein monomers, exclusively found in sieve elements (SEs) of legumes. Forisomes block the phloem mass flow by a Ca2+-induced conformational change (swelling and rounding). We studied the forisome reactivity in four different legume species-Medicago sativa, Pisum sativum, Trifolium pratense and Vicia faba. Depending on the species, we found direct relationships between SE diameter, forisome surface area and distance from the leaf tip, all indicative of a developmentally tuned regulation of SE diameter and forisome size. Heat-induced forisome dispersion occurred later with increasing distance from the stimulus site. T. pratense and V. faba dispersion occurred faster for forisomes with a smaller surface area. Near the stimulus site, electro potential waves (EPWs)-overlapping action (APs), and variation potentials (VPs)-were linked with high full-dispersion rates of forisomes. Distance-associated reduction of forisome reactivity was assigned to the disintegration of EPWs into APs, VPs and system potentials (SPs). Overall, APs and SPs alone were unable to induce forisome dispersion and only VPs above a critical threshold were capable of inducing forisome reactions.

Detection of Different Hosts From a Distance Alters the Behaviour and Bioelectrical Activity of Cuscuta racemosa

In our study, we investigated some physiological and ecological aspects of the life of Cuscuta racemosa Mart. (Convolvulaceae) plants with the hypothesis that they recognise different hosts at a distance from them, and they change their survival strategy depending on what they detect. We also hypothesised that, as an attempt of prolonging their survival through photosynthesis, the synthesis of chlorophylls (a phenomenon not completely explained in these parasitic plants) would be increased if the plants don't detect a host. We quantified the pigments related to photosynthesis in different treatments and employed techniques such as electrophysiological time series recording, analyses of the complexity of the obtained signals, and machine learning classification to test our hypotheses. The results demonstrate that the absence of a host increases the amounts of chlorophyll a, chlorophyll b, and β-carotene in these plants, and the content varied depending on the host presented. Besides, the electrical signalling of dodders changes according to the species of host perceived in patterns detectable by machine learning techniques, suggesting that they recognise from a distance different host species. Our results indicate that electrical signalling might underpin important processes such as foraging in plants. Finally, we found evidence for a likely process of attention in the dodders toward the host plants. This is probably to be the first empirical evidence for attention in plants and has important implications on plant cognition studies.

Imidacloprid-mediated stress on non-Bt and Bt cotton, aphid and ladybug interaction: Approaches based on insect behaviour, fluorescence, dark respiration and plant electrophysiology

Plants and insects are parts of a complex system that involves interactions among many trophic levels, and it is important to understand the nature of such interactions. In the complex of interactions involving aphids and transgenic cotton expressing Bacillus thuringiensis, both the spraying of neonicotinoids and the occurrence of predatory coccinellids are common. However, there are gaps regarding the knowledge about possible impacts of neonicotinoids on physiological variables of the host plant and behavioural traits of the aphid (Aphis gossypii) and predator (Cycloneda sanguinea). Therefore, this study aimed to highlight the photosynthetic and electrical responses of the plant to the stress caused by the aphid attack combined with the stress generated by the use of imidacloprid in Bt and non-Bt cotton (Gossypium hirsutum L.) cultivars and to evaluate how this stress can influence the behavioural ecology of the predator and prey. Chlorophyll a fluorescence tests, dark respiration and electrophysiology on non-Bt and Bt cotton were carried out, the behaviour of the prey and predator was also evaluated with a video capture system. Our research is a study model that generates insights about possible impacts when using Imidacloprid without the occurrence of the pest on the plant, because the exposure of non-Bt and Bt cotton plants and the predator to imidacloprid unnecessarily, may result in stress on the physiology of the cotton plants and on the behaviour of the predator.

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.

Glyphosate-dependent effects on photosynthesis of Solanum lycopersicum L.-An ecophysiological, ultrastructural and molecular approach

This study aimed to assess the toxicity of glyphosate (GLY; 0, 10, 20 and 30 mg kg-1) in Solanum lycopersicum L., particularly focusing on the photosynthetic metabolism. By combining ecophysiological, ultrastructural, biochemical and molecular tools, the results revealed that the exposure of tomato plants to GLY led to alterations in leaf water balance regulation [increasing stomatal conductance (gs) and decreasing water use efficiency (WUEi) at higher concentrations] and induced slight alterations in the structural integrity of cells, mainly in chloroplasts, accompanied by a loss of cell viability. Moreover, the transcriptional and biochemical control of several photosynthetic-related parameters was reduced upon GLY exposure. However, in vivo chlorophyll fluorometry and IRGA gas-exchange studies revealed that the photosynthetic yield of S. lycopersicum was not repressed by GLY. Overall, GLY impacts cellular and subcellular homeostasis (by affecting chloroplast structure, reducing photosynthetic pigments and inhibiting photosynthetic-related genes transcription), and leaf structure, but is not reducing the carbon flow on a leaf area basis. Altogether, these results suggest a trade-off effect in which GLY-induced toxicity is compensated by a higher photosynthetic activity related to GLY-induced dysfunction in gs and an increase in mesophyll thickness/density, allowing the viable leaf cells to maintain their photosynthetic capacity.

Glutamate and NMDA affect cell excitability and action potential dynamics of single cell of macrophyte Nitellopsis obtusa

The effect of glutamate and N-methyl-d-aspartate (NMDA) on electrical signalling - action potentials (AP) and excitation current transients - was studied in intact macrophyte Nitellopsis obtusa (Characeaen) internodal cell. Intracellular glass electrode recordings of single cell in current clamp and two-electrode voltage clamp modes indicate that glutamate (Glu, 0.1-1.0 mM) and NMDA (0.01-1.0 mM) increase electrically induced AP amplitude by hyperpolarising excitation threshold potential (Eth) and prolong AP fast repolarisation phase. Amplitude of Cl- current transient, as well as its activation and inactivation durations were also increased. Both Glu and NMDA act in a dose-dependent manner. The effect of NMDA exceeds that of Glu. Ionotropic glutamate receptor inhibitors AP-5 (NMDA-type receptors) and DNQX (AMPA/Kainate-type) have no effect on Nitellopsis cell electrical signalling per se, yet robustly inhibit excitatory effect of NMDA. This study reinforces NMDA as an active component in glutamatergic signalling at least in some plants and stresses the elaborate fine-tuning of electrical signalling.

Development and application of photoconversion fluoropolymer films for greenhouses located at high or polar latitudes

To convert and store energy in the process of photosynthesis, plants primarily use quanta of the red and blue parts of the spectrum. At high latitudes, the average daily intensity of red and blue parts of the spectrum is not very high; for many crops cultivated under greenhouse conditions, it reaches the sufficient level only on clear summer days. The problem of insufficient illumination in greenhouses is usually solved with artificial light sources. This article describes a technology for the manufacture of photoconversion fluoropolymer films for greenhouses. The fluoropolymer films described in the paper make use of original gold nanoparticles and nanoparticles with fluorescence in the blue or red region of the spectrum. In the polymer film, nanoparticles aggregate in the form of "beads", which enhances the field of the optical wave. The film photoconverts UV and violet light into blue and red light. Gold nanoparticles also partially convert energy in the green region of the spectrum (not used by plants) into heat, which is also important for agriculture at high latitudes. In addition, impregnation of gold nanoparticles into fluoropolymer significantly increases the lifetime of the film. The films described in the paper can significantly increase the productivity of greenhouses located at high latitudes. Plants cultivated under the films have more chlorophyll and a higher intensity of photosynthesis - although their system of distance stress signals is, to a certain degree, suppressed.