Potential Of Variants Research Articles

Analysis of Molecular Mechanisms of Chronic Irradiation Effects on Electrical Signals in Wheat Plants

The effect of ionizing radiation (IR) on plants is mainly realized by altering the status of signaling systems and modifying stress signals. Variation potential (VP) is one of the types of electrical signals in plants. IR contributes to an increase in the amplitude of the VP, but the mechanisms of such influence are practically unknown. A possible way to implement changes arising from the action of IR is the regulation of gene expression. In the present work, the changes in the gene expression of participants in the generation and propagation of VP in irradiated plants are investigated. The experiments were performed on 14–15-day-old soft wheat plants (Triticum aestivum L.) grown under chronic irradiation (source 90Sr-90Y) with a dose rate of 31.3 μGy/h. The maximum accumulated dose was about 11.3 mGy. The irradiated plants showed no changes in the expression of calcium (TPC1), anionic (ALMT1 and CLC1), potassium (AKT1) channels, H+-ATPase (HA1), and NADPH oxidase (RBOHs) genes. A decrease in the expression of the SKOR potassium channel gene was revealed. The potassium channel blocker, tetraethylammonium chloride, caused an increase in response amplitude in control plants comparable to the increase in amplitude in the irradiated group. The obtained results indicate that one of the ways IR influences the electrical signals of plants is to inhibit the expression of the potassium channel.

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.

Stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees

Electrical plant signaling as a variation potential (VP) occurs in response to a wide range of stimuli, and it is associated with the induction of sudden changes in xylem pressure. Additionally, there is evidence that electrical potential (EP) of plants changes with changing soil water content. Therefore, the use of EP as a direct plant measurement of plant water status may have potential as water stress monitoring information. EP measurements within plant stems indirectly correlate with sap flow (SF), which is one possible variable for estimating plant water use. However, whether this relationship is stable under drought conditions is not known. The present work investigated the relationships between SF and EP variations during an 18-day drought period on three avocado trees to test the hypothesis that the relationships between SF and EP may be lost due to drought intensity. The results showed that short-term variations in EP were positively associated with vapor pressure deficit (VPD) and SF variations but negatively associated with soil water content (SWC). An increase in VP emissions was observed as drought advanced, which was negatively associated with stem water potential (SWP). After 18 days of drought, irrigation almost completely suppressed short-term variations in EP. The present work provides preliminary results that strongly suggest a relationship between drought stress and EP variations in plant stems. Further research is needed to confirm whether the EP trends observed during drought are due to cavitation events and emission of VP signals and/or linked to other physiological processes, e.g., pH changes in response to drought or embolism. Meanwhile, the present work indicates that short-term variations in EP (dEP) are strongly associated with the intensity of drought stress, thus stem electrical potential variations may aid in the early detection of drought stress in fruit-bearing trees.

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.

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.

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.

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.

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.

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

ABSTRACT 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.

Multivariate characterization of spontaneously generated electrical signals evoked by electrical stimulation in abscisic acid mutant tomato plants

In vivo monitoring of electrical activity between plant tissues and organs can be used to study information transport mechanisms and physiological responses to external stimuli. These signals are mainly characterized as action potential (AP) and variation potential (VP), related to long- and short-distance signaling, respectively. Spontaneous action potentials (SAPs) may also occur in the absence of known stimuli at frequencies adjusted to environmental conditions. By contrast, the mechanism of spontaneous depolarizations (SDs) remain unknown. In this work, spontaneous generation and evocation of electrical signals via electrical stimulation were monitored for 72 h using Ag/AgCl electrodes inserted into the stem and petioles of two mutant tomatoes, cv. Micro-Tom notabilis (MTnot) and MTsp12::NCED (MTNCED), and wild type (MTwt). MTnot generated more SAPs than did MTwt and MTNCED, propagated through the stem and petioles, with a transmission speed of 0.50 cm min− 1. SDs propagation occurred mainly in the early morning, most often in MTwt. MTNCED gave a lower number of SDs that were associated with membrane depolarization level. The electrical stimuli promoted the generation of APs in all studied genotypes. Mutants MTnot and MTNCED were less sensitive to electrical stimulation, requiring greater stimuli to reach the excitation threshold.

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.

Spatial and Temporal Dynamics of Electrical and Photosynthetic Activity and the Content of Phytohormones Induced by Local Stimulation of Pea Plants.

A local leaf burning causes variation potential (VP) propagation, a decrease in photosynthesis activity, and changes in the content of phytohormones in unstimulated leaves in pea plants. The VP-induced photosynthesis response develops in two phases: fast inactivation and long-term inactivation. Along with a decrease in photosynthetic activity, there is a transpiration suppression in unstimulated pea leaves, which corresponds to the long-term phase of photosynthesis response. Phytohormone level analysis showed an increase in the concentration of jasmonic acid (JA) preceding a transpiration suppression and a long-term phase of the photosynthesis response. Analysis of the spatial and temporal dynamics of electrical signals, phytohormone levels, photosynthesis, and transpiration activity showed the most pronounced changes in the more distant leaf from the area of local stimulation. The established features are related to the architecture of the vascular bundles in the pea stem.

Shear-Enhanced Dispersion of a Wound Substance as a Candidate Mechanism for Variation Potential Transmission.

A variation potential (VP) is an electrical signal unique to plants that occurs in response to wounding or flaming. The propagation mechanism itself, however, is known not to be electrical. Here we examine the hypothesis that VP transmission occurs via the transport of a chemical agent in the xylem. We assume the electrical signal is generated locally by the activation of an ion channel at the plasma membrane of cells adjacent to the xylem. We work on the assumption that the ion channels are triggered when the chemical concentration exceeds a threshold value. We use numerical computations to demonstrate the combined effect of advection and diffusion on chemical transport in a tube flow, and propose shear-enhanced Taylor-Aris dispersion as a candidate mechanism to explain VP rates observed in experiments.

Circulating tumor DNA molecular profiling in rare cancer patients from the MASTER KEY Project.

e14532 Background: In April 2017, MASTER KEY Project, composed of a prospective registry study part and a multiple clinical trials part, was established to promote treatment development for rare cancers, which is lacking standard or investigational therapeutic options. Circulating tumor DNA (ctDNA) analysis by next-generation sequencing (NGS) has provided new insight into personalized medicine in a more accessible, non-invasive manner; however, most reports are focused on common cancers. We report genetic alterations detected by ctDNA NGS analysis in rare solid cancers. Methods: Prospectively consented patients (pts), also enrolled in MASTER KEY registry study, had ctDNA NGS testing at a CLIA-certified lab (Guardant360) for point mutations, indels, copy number amplifications, fusions, and microsatellite instability. Alterations were assessed for incidence according to cancer type, functional impact, therapeutic implications, and comparison with tissue NGS. Main inclusion criteria: 1) age ≥16, 2) histological diagnosis of rare cancer (annual incidence less than 6 cases per 100,000 population), cancer of unknown primary (CUP), or rare tissue subtypes of common cancers, 3) active metastatic / unresectable cancer, 4) a written consent. Results: From Nov. 2018 to Jan 2019, 50 pts had Guardant360 testing. Diseases included: soft tissue sarcoma (28), ovarian carc. (7), CUP (4), salivary gland tumor (3), thyroid carc. (2), GIST (1), adrenal cortical carc. (1), rare subtype of GI tract (1), malignant mesothelioma (1), nephroblastoma (1), NET (1), NUT carc. (1). All Japanese, male/female = 14/36, median age 61, ECOG performance status 0/1/2/3 = 30/19/0/1. 76% of pts (38/50) had ≥1 alteration detected, with median number of 2 alterations (range: 0-9), with VAF(0.1-60.3%); 87%(33/38) of those pts had a variant most likely pathogenic; 61% (20/33) of those pts had a variant potential for clinical action. Mean TAT was 10.3 days. 19 pts had tissue NGS testing and in 3 pts, alterations were detected by ctDNA NGS but not by tissue NGS. Updated results of 100 patients will be presented at the conference. Conclusions: Most rare cancer patients with advanced disease had a detectable genomic alteration by Guardant360. Clinical trial information: UMIN000034394.

Impact of Local Damage on Transpiration of Pea Leaves at Various Air Humidity

Local damages induce a wide spectrum of functional responses in intact parts of the plant, including changes in transpiration and CO2 assimilation, which may be associated with propagating variation potential (VP). In the present work carried out on pea (Pisum sativum L.) plants, an analysis of the influence of local burn leading to generation of VP on transpiration and CO2 assimilation under conditions of different air humidity was conducted. It was shown that VP induced multiphase changes in these physiological functions in intact pea leaf, including rapid lowering their parameters, slow elevation of them, and prolonged dropping transpiration and assimilation. Analysis of the impact of air humidity on these processes showed that quick and long lowering transpiration was significantly suppressed under the conditions of high humidity, while slowly increasing transpiration hardly depended on air humidity. Dependence of VP-induced CO2 assimilation response on air humidity exhibited a similar character. Additional correlation analysis of amplitudes of VP-induced transpiration and CO2 assimilation changes showed that prolonged stomata closing may be the mechanism of long-term lowering assimilation of intact leaves after the action of local burn. In general, it was established that the VP-induced transpiration response is a complex combination of activation and suppression of transpiration, and the contribution of different components to the observed responses depends on air humidity.

Chemical agents transported by xylem mass flow propagate variation potentials.

SummaryLong‐distance signalling is important for coordinating plant responses to the environment. Variation potentials (VPs) are a type of long‐distance electrical signal that are generated in plants in response to wounding or flaming. Unlike self‐propagating action potentials, VPs can be measured beyond regions of dead or chemically treated tissue that block signal generation, suggesting a different mode of propagation. Two alternative propagation mechanisms have been proposed: movement of a chemical agent and a pressure wave through the vasculature. Variants of these two signalling mechanisms have been suggested. Here, we use simple models of the underlying physical processes to evaluate and compare these predictions against independent data. Our models suggest that chemical diffusion and pressure waves are unlikely to capture existing data with parameters that are known from other sources. The previously discarded hypothesis of mass flow in the xylem transporting a chemical agent, however, is able to reproduce experimental propagation speeds for VPs. We therefore suggest that chemical agents transported by mass flow within the xylem are more likely than a pressure wave or chemical diffusion as a VP propagation mechanism. Understanding this mode of long‐distance signalling within plants is important for unravelling how plants coordinate physiological responses via cell‐to‐cell communication.

Parameters of electrical signals and photosynthetic responses induced by them in pea seedlings depend on the nature of stimulus.

Local damage induces generation and propagation of variation potentials (VPs) that affect physiological processes in plants. The aims of the work presented here were to investigate parameters of VP induced by burning, heating and mechanical injury in pea seedlings, and to undertake a theoretical analysis of the mechanisms underlying the differences in VP parameters and a study of the photosynthetic responses caused by VPs induced by the damaging factors. The velocity of propagation of burn-induced VP decreased with distance from the damaged area whereas the velocities of heating- and injury-induced VPs were constant. The amplitudes of burn- and heating-induced VPs did not depend on distance whereas the amplitude of VP induced by mechanical injury decreased. VP propagation has been simulated on the basis of wound substance spread. The simulation revealed two possible ways of wound substance propagation: turbulent diffusion from the damaged area and secondary active production in intact cells. The photosynthetic response (decrease in the quantum yield of PSII and raising the level of non-photochemical fluorescence quenching (NPQ)) developed in case of VP entering the intact leaf under heating and burn but was not registered after mechanical injury. An increase in NPQ level was biphasic under burn in comparison with a single-phase one under heating, and the NPQ amplitude was slightly higher under burn. We suggest that differences in photosynthetic responses may be determined by the parameters of VPs induced by stimuli of different nature.

Age-dependent changes of photosynthetic responses induced by electrical signals in wheat seedlings

Electrical signals in plants, namely, the action potential (AP) and variation potential (VP) alter the activity of many processes, including photosynthesis. The functional responses induced by electrical signals vary in direction and amplitude, which might be determined by variable conditions of plants prior to stimulation, by the development stage in particular. In this work, the parameters of VP-induced photosynthetic responses were analyzed at various stages of wheat seedling development. Local wounding of the second leaf in wheat plants induced the propagation of VP and altered the activity of photosynthesis at a distance from the wound location. The amplitude of VP was enlarged when the seedling age increased from 11 to 18 days. The VP-induced photosynthetic response changed with age both qualitatively and quantitatively. The amplitude of VP-induced changes in CO2 assimilation and nonphotochemical quenching (NPQ) increased with age, which might be due to the increase in VP amplitude and associated changes in Ca2+ and H+ concentrations. The quantum yield of photosystem II photoreaction was subject to age-dependent changes: the photochemical quantum yield (γ(PSII)) was found to increase after VP in young leaves, whereas the decline in γ(PSII) was observed after the VP propagation in mature leaves. The results may explain the diversity of photosynthetic responses caused by the electrical signals.

Application of a mathematical model of variation potential for analysis of its influence on photosynthesis in higher plants

Local injuries induce generation of variation potential (VP) in higher plants; VP propagates into intact parts of a plant and induces the photosynthesis inactivation, which is probably connected with a proton influx into the cells. The aim of this work was to theoretically investigate participation of the intra- and extracellular pH changes in this process using the VP mathematical model developed earlier. The VP model took into account main systems of ion transport in a cell and their regulation; concentrations of the potential-forming ions; buffering properties, and the involvement of a “wound substance” in a signal propagation. To describe the dependence of the photosynthetic parameters on the pH changes, experimentally obtained linear relations were used. The model was shown to give a good qualitative description of the photosynthetic response at a distance of 10 cm from the injury area and simulated a considerable attenuation of the response at a distance of 22 cm. Analysis of the dependence of the photosynthetic response parameters on the VP amplitude also showed a qualitative correspondence of the model with the experimental results. Thus, experimental photosynthetic response is described well by the VP model that presumes linear dependencies of the photosynthetic parameter changes on pH shifts. This theoretical result supports a hypothesis about a key role of pH shifts in the development of the photosynthetic response.

Changes in H(+)-ATP Synthase Activity, Proton Electrochemical Gradient, and pH in Pea Chloroplast Can Be Connected with Variation Potential.

Local stimulation induces generation and propagation of electrical signals, including the variation potential (VP) and action potential, in plants. Burning-induced VP changes the physiological state of plants; specifically, it inactivates photosynthesis. However, the mechanisms that decrease photosynthesis are poorly understood. We investigated these mechanisms by measuring VP-connected systemic changes in CO2 assimilation, parameters of light reactions of photosynthesis, electrochromic pigment absorbance shifts, and light scattering. We reveal that inactivation of photosynthesis in the pea, including inactivation of dark and light reactions, was connected with the VP. Inactivation of dark reactions decreased the rate constant of the fast relaxation of the electrochromic pigment absorbance shift, which reflected a decrease in the H+-ATP synthase activity. This decrease likely contributed to the acidification of the chloroplast lumen, which developed after VP induction. However, VP-connected decrease of the proton motive force across the thylakoid membrane, possibly, reflected a decreased pH in the stroma. This decrease may be another mechanism of chloroplast lumen acidification. Overall, stroma acidification can decrease electron flow through photosystem I, and lumen acidification induces growth of fluorescence non-photochemical quenching and decreases electron flow through photosystem II, i.e., pH decreases in the stroma and lumen, possibly, contribute to the VP-induced inactivation of light reactions of photosynthesis.