Electrophysiological assessment of water stress in fruit-bearing woody plants

A library of electrophysiological responses in plants - a model of transversal education and open science

Electrophysiology in plants is understudied, and, moreover, an ideal model for student inclusion at all levels of education. Here, we report on an investigation in open science, whereby scientists worked with high school students, faculty, and undergraduates from Chile, Germany, Serbia, South Korea, and the USA. The students recorded the electrophysiological signals of >15 plant species in response to a flame or tactile stimulus applied to the leaves. We observed that approximately 60% of the plants studied showed an electrophysiological response, with a delay of ~ 3-6 s after stimulus presentation. In preliminary conduction velocity experiments, we verified that observed signals are indeed biological in origin, with information transmission speeds of ~ 2-9 mm/s. Such easily replicable experiments can serve to include more investigators and students in contributing to our understanding of plant electrophysiology.

Functions and Regulatory Mechanisms of bHLH Transcription Factors during the Responses to Biotic and Abiotic Stresses in Woody Plants

Environmental stresses, including abiotic and biotic stresses, have complex and diverse effects on the growth and development of woody plants, which have become a matter of contention due to concerns about the outcomes of climate change on plant resources, genetic diversity, and world food safety. Plant basic helix-loop-helix (bHLH) transcription factors (TFs) are involved in a variety of physiological processes and play an important role in biotic and abiotic stress responses of woody plants. In recent years, an increasing body of studies have been conducted on the bHLH TFs in woody plants, and the roles of bHLH TFs in response to various stresses are increasingly clear and precise. Therefore, it is necessary to conduct a systematic and comprehensive review of the progress of the research of woody plants. In this review, the structural characteristics, research history and roles in the plant growth process of bHLH TFs are summarized, the gene families of bHLH TFs in woody plants are summarized, and the roles of bHLH TFs in biotic and abiotic stresses in woody plants are highlighted. Numerous studies mentioned in this review have shown that bHLH transcription factors play a crucial role in the response of woody plants to biotic and abiotic stresses. This review serves as a reference for further studies about enhancing the stress resistance and breeding of woody plants. Also, the future possible research directions of bHLH TFs in response to various stresses in woody plants will be discussed.

Evaluating Bacterial Nanocellulose Interfaces for Recording Surface Biopotentials from Plants

The study of plant electrophysiology offers promising techniques to track plant health and stress in vivo for both agricultural and environmental monitoring applications. Use of superficial electrodes on the plant body to record surface potentials may provide new phenotyping insights. Bacterial nanocellulose (BNC) is a flexible, optically translucent, and water-vapor-permeable material with low manufacturing costs, making it an ideal substrate for non-invasive and non-destructive plant electrodes. This work presents BNC electrodes with screen-printed carbon (graphite) ink-based conductive traces and pads. It investigates the potential of these electrodes for plant surface electrophysiology measurements in comparison to commercially available standard wet gel and needle electrodes. The electrochemically active surface area and impedance of the BNC electrodes varied based on the annealing temperature and time over the ranges of 50 °C to 90 °C and 5 to 60 min, respectively. The water vapor transfer rate and optical transmittance of the BNC substrate were measured to estimate the level of occlusion caused by these surface electrodes on the plant tissue. The total reduction in chlorophyll content under the electrodes was measured after the electrodes were placed on maize leaves for up to 300 h, showing that the BNC caused only a 16% reduction. Maize leaf transpiration was reduced by only 20% under the BNC electrodes after 72 h compared to a 60% reduction under wet gel electrodes in 48 h. On three different model plants, BNC-carbon ink surface electrodes and standard invasive needle electrodes were shown to have a comparable signal quality, with a correlation coefficient of >0.9, when measuring surface biopotentials induced by acute environmental stressors. These are strong indications of the superior performance of the BNC substrate with screen-printed graphite ink as an electrode material for plant surface biopotential recordings.

Variations of electric potential in the xylem of tree trunks associated with water content rhythms

Instantaneous electrical responses in plants have been widely studied, but the mechanism of spontaneous, periodic electric potential alternations in the xylem of tree trunks remains controversial. The generation of the electric potential can be explained by the electrode potential, which depends on ion concentrations near electrodes. However, several different hypotheses about its periodic variations have been proposed, including streaming potential, ion diffusion, charge transport, and oxygen turnover. Here, we performed long-term measurements on the electric potential and water content in the xylem of trees, and observed changes in the electric potential and transpiration rate in response to varied numbers of leaves, light radiation, temperature, and relative air humidity. The electric potential showed a distinct seasonal trend, combined with daily rhythms, and could be affected by environmental changes. Rapid changes in the electric potential routinely lagged behind those of the transpiration rate, but their ranges of change were proportional. Both annual and diurnal patterns of the electric potential were synchronous with the trees' water content. Moreover, we found potential function relationships between the electric potential and water content. Accordingly, we propose a new perspective, that the variations of the electric potential in tree xylem could be associated with water content rhythms.

Osmotic stress decreases complexity underlying the electrophysiological dynamic in soybean

Studies on plant electrophysiology are mostly focused on specific traits of single cells. Inspired by the complexity of the signalling network in plants, and by analogy with neurons in human brains, we sought evidence of high complexity in the electrical dynamics of plant signalling and a likely relationship with environmental cues. An EEG-like standard protocol was adopted for high-resolution measurements of the electrical signal in Glycine max seedlings. The signals were continuously recorded in the same plants before and after osmotic stimuli with a -2 MPa mannitol solution. Non-linear time series analyses methods were used as follows: auto-correlation and cross-correlation function, power spectra density function, and complexity of the time series estimated as Approximate Entropy (ApEn). Using Approximate Entropy analysis we found that the level of temporal complexity of the electrical signals was affected by the environmental conditions, decreasing when the plant was subjected to a low osmotic potential. Electrical spikes observed only after stimuli followed a power law distribution, which is indicative of scale invariance. Our results suggest that changes in complexity of the electrical signals could be associated with water stress conditions in plants. We hypothesised that the power law distribution of the spikes could be explained by a self-organised critical state (SOC) after osmotic stress.

Plant Science View on Biohybrid Development

Biohybrid consists of a living organism or cell and at least one engineered component. Designing robot-plant biohybrids is a great challenge: it requires interdisciplinary reconsideration of capabilities intimate specific to the biology of plants. Envisioned advances should improve agricultural/horticultural/social practice and could open new directions in utilization of plants by humans. Proper biohybrid cooperation depends upon effective communication. During evolution, plants developed many ways to communicate with each other, with animals, and with microorganisms. The most notable examples are: the use of phytohormones, rapid long-distance signaling, gravity, and light perception. These processes can now be intentionally re-shaped to establish plant-robot communication. In this article, we focus on plants physiological and molecular processes that could be used in bio-hybrids. We show phototropism and biomechanics as promising ways of effective communication, resulting in an alteration in plant architecture, and discuss the specifics of plants anatomy, physiology and development with regards to the bio-hybrids. Moreover, we discuss ways how robots could influence plants growth and development and present aims, ideas, and realized projects of plant-robot biohybrids.

Evidence for the Involvement of Electrical, Calcium and ROS Signaling in the Systemic Regulation of Non-Photochemical Quenching and Photosynthesis

In contrast to the function of reactive oxygen species, calcium, hormones and small RNAs in systemic signaling, systemic electrical signaling in plants is poorly studied and understood. Pulse amplitude-modulated Chl fluorescence imaging and surface electrical potential measurements accompanied by pharmacological treatments were employed to study stimuli-induced electrical signals in leaves from a broad range of plant species and in Arabidopsis thaliana mutants. Here we report that rapid electrical signals in response to a local heat stimulus regulate systemic changes in non-photochemical quenching (NPQ) and PSII quantum efficiency. Both stimuli-induced systemic changes in NPQ and photosynthetic capacity as well as electrical signaling depended on calcium channel activity. Use of an Arabidopsis respiratory burst oxidase homolog D (RBOHD) mutant (rbohD) as well as an RBOH inhibitor further suggested a cross-talk between ROS and electrical signaling. Our results suggest that higher plants evolved a complex rapid long-distance calcium-dependent electrical systemic signaling in response to local stimuli that regulates and optimizes the balance between PSII quantum efficiency and excess energy dissipation in the form of heat by means of NPQ.

Research on the Effect of Electrical Signals on Growth of Sansevieria under Light-Emitting Diode (LED) Lighting Environment

The plant electrical signal has some features, e.g. weak, low-frequency and time-varying. To detect changes in plant electrical signals, LED light source was used to create a controllable light environment in this study. The electrical signal data were collected from Sansevieria leaves under the different illumination conditions, and the data was analyzed in time domain, frequency domain and time–frequency domain, respectively. These analyses are helpful to explore the relationship between changes in the light environment and electrical signals in Sansevieria leaves. The changes in the plant electrical signal reflected the changes in the intensity of photosynthesis. In this study, we proposed a new method to express plant photosynthetic intensity as a function of the electrical signal. That is, the plant electrical signal can be used to describe the state of plant growth.

Use of plant woody species electrical potential for irrigation scheduling

The electrical response of plants to environmental stimuli can be measured and quantitatively related to the intensity of several stimulating sources, like temperature, solar radiation, soil water content, evapotranspiration rates, sap flow and dendrometric cycles. These relations can be used to assess the influence of different environmental situations on soil water availability to plants, defined as a steady state condition between leaf transpirative flow and soil water flow to plant roots. A restricted soil water flow due to soil dryness can trigger water stress in plants, if the atmospheric evaporative demand is high, causing partial stomata closure as a physiological response to avoid plant dehydration; water stressed and unstressed plants manifest a differential electrical response. Real time plant electrical response measurements can anticipate actions that prevent the plant reaching actual stress conditions, optimizing stomata gas exchange and photosynthetic rates. An electrophysiological sensor developed in this work, allows remote real-time recording information on plant electrical potential (EP) in the field, which is highly related to EP measurements obtained with a laboratory Keithley voltmeter sensor used in an highly controlled experimental setup. Our electrophysiological sensor is a wireless, autonomous devise, which transmits EP information via Internet to a data server. Using both types of sensors (EP electrodes with a Keithley voltmeter and the electrophysiological sensor), we measured in real time the electrical responses of Persea americana and Prunus domestica plants, to induced water deficits. The differential response for 2 scenarios: irrigation and water restriction is identified by a progressive change in slope on the daily maximal and minimal electric signal values in stressed plants, and a zero-slope for similar signals for well-watered plants. Results show a correspondence between measured signals obtained by our electrophysiological sensor and the EP electrodes connected to the Keithley voltmeter in each irrigation stage. Also, both sensors show a daily cyclical signal (circadian cycle).