Luis Gurovich

Evidence for the transmission of information through electric potentials in injured avocado trees

Electrical excitability and signaling, frequently associated with rapid responses to environmental stimuli, have been documented in both animals and higher plants. The presence of electrical potentials (EPs), such as action potentials (APs) and variation potentials (VPs), in plant cells suggests that plants make use of ion channels to transmit information over long distances. The reason why plants have developed pathways for electrical signal transmission is most probably the necessity to respond rapidly, for example, to environmental stress factors. We examined the nature and specific characteristics of the electrical response to wounding in the woody plant Persea americana (avocado). Under field conditions, wounds can be the result of insect activity, strong winds or handling injury during fruit harvest. Evidence for extracellular EP signaling in avocado trees after mechanical injury was expressed in the form of variation potentials. For tipping and pruning, signal velocities of 8.7 and 20.9 cm/s, respectively, were calculated, based on data measured with Ag/AgCl microelectrodes inserted at different positions of the trunk. EP signal intensity decreased with increasing distance between the tipping and pruning point and the electrode. Recovery time to pre-tipping or pre-pruning EP values was also affected by the distance and signal intensity from the tipping or pruning point to the specific electrode position. Real time detection of remote EP signaling can provide an efficient tool for the early detection of insect attacks, strong wind damage or handling injury during fruit harvest. Our results indicate that electrical signaling in avocado, resulting from microenvironment modifications, can be quantitatively related to the intensity and duration of the stimuli, as well as to the distance between the stimuli site and the location of EP detection. These results may be indicative of the existence of a specific kind of proto-nervous system in plants.

Electrical signaling, stomatal conductance, ABA and Ethylene content in avocado trees in response to root hypoxia

Avocado (Persea americana Mill.) trees are among the most sensitive of fruit tree species to root hypoxia as a result of flooded or poorly drained soil. Similar to drought stress, an early physiological response to root hypoxia in avocado is a reduction of stomatal conductance. It has been previously determined in avocado trees that an extracellular electrical signal between the base of stem and leaves is produced and related to reductions in stomatal conductance in response to drought stress. The current study was designed to determine if changes in the extracellular electrical potential between the base of the stem and leaves in avocado trees could also be detected in response to short-term (min) or long-term (days) root hypoxia, and if these signals could be related to stomatal conductance (gs), root and leaf ABA and ACC concentrations, ethylene emission from leaves and leaf abscission. In contrast to previous observations for drought-stressed trees, short-term or long-term root hypoxia did not stimulate an electrical potential difference between the base of the stem and leaves. Short-term hypoxia did not result in a significant decrease in gs compared with plants in the control treatment, and no differences in ABA concentration were found between plants subjected to hypoxia and control plants. Long-term hypoxia in the root zone resulted in a significant decrease in gs, increased leaf ethylene and increased leaf abscission. The results indicate that for avocado trees exposed to root hypoxia, electrical signals do not appear to be the primary root-to-shoot communication mechanism involved in signaling for stomatal closure as a result of hypoxia in the root zone.

Electrical signals in avocado trees: Responses to light and water availability conditions

Plant responses to environmental changes are associated with electrical excitability and signalling; automatic and continuous measurements of electrical potential differences (ΔEP) between plant tissues can be effectively used to study information transport mechanisms and physiological responses that result from external stimuli on plants. The generation and conduction of electrochemical impulses within plant different tissues and organs, resulting from abiotic and biotic changes in environmental conditions is reported. In this work, electrical potential differences are monitored continuously using Ag/AgCl microelectrodes, inserted 5 mm deep into sapwood at two positions in the trunks of several Avocado trees. Electrodes are referenced to a non polarisable Ag/AgCl microelectrode installed 20 cm deep in the soil. Systematic patterns of ΔEP during absolute darkness, day-night cycles and different conditions of soil water availability are discussed as alternative tools to assess early plant stress conditions.

Electrophysiological assessment of water stress in fruit-bearing woody plants.

Development and evaluation of a real-time plant water stress sensor, based on the electrophysiological behavior of fruit-bearing woody plants is presented. Continuous electric potentials are measured in tree trunks for different irrigation schedules, inducing variable water stress conditions; results are discussed in relation to soil water content and micro-atmospheric evaporative demand, determined continuously by conventional sensors, correlating this information with tree electric potential measurements. Systematic and differentiable patterns of electric potentials for water-stressed and no-stressed trees in 2 fruit species are presented. Early detection and recovery dynamics of water stress conditions can also be monitored with these electrophysiology sensors, which enable continuous and non-destructive measurements for efficient irrigation scheduling throughout the year. The experiment is developed under controlled conditions, in Faraday cages located at a greenhouse area, both in Persea americana and Prunus domestica plants. Soil moisture evolution is controlled using capacitance sensors and solar radiation, temperature, relative humidity, wind intensity and direction are continuously registered with accurate weather sensors, in a micro-agrometeorological automatic station located at the experimental site. The electrophysiological sensor has two stainless steel electrodes (measuring/reference), inserted on the stem; a high precision Keithley 2701 digital multimeter is used to measure plant electrical signals; an algorithm written in MatLab(®), allows correlating the signal to environmental variables. An electric cyclic behavior is observed (circadian cycle) in the experimental plants. For non-irrigated plants, the electrical signal shows a time positive slope and then, a negative slope after restarting irrigation throughout a rather extended recovery process, before reaching a stable electrical signal with zero slope. Well-watered plants presented a continuous signal with daily maximum and a minimum EP of similar magnitude in time, with zero slope. This plant electrical behavior is proposed for the development of a sensor measuring real-time plant water status.

The electrical response of fruit trees to soil water availability and diurnal light-dark cycles

Recent studies have associated the effect of water stress, irrigation, and light cycles with electrical signaling in fruit tree species including avocado, blueberry, lemon and olive. In those studies, changes in the electrical potential (EP) difference were detected between the base of the stem and leaf in response to drought, irrigation, and diurnal changes in light and dark. In avocado, the changes in EP between the base of the stem and leaf petiole (ΔVL-S) observed in response to decreased soil water content have been associated with a decrease in stomatal conductance, indicating that stomatal closure might be associated with an electrical signal. New experiments were conducted to determine the effects of short- and long-term drought on root to leaf electrical signaling in avocado confirming that in both situations significant changes in EP differences can be detected and that an extra-cellular electrical signal appears to be involved in root to leaf communication initiating stomatal closure. Day-to-night fluctuations in EP observed in fruit trees appeared to correspond to the time of day and were therefore presumably affected by diurnal changes in ambient light and vapor pressure deficit. Addendum to: Gil PM, Gurovich L, Schaffer B, Alcayaga J, Rey S, Iturriaga R. Root to leaf electrical signaling in avocado in response to light and soil water content. J Plant Physiol 2008; 165:1070-8.

Experimental Evaluation of Agricultural Drains

AbstractCurrent models used to design agricultural drains assume that perforated pipes (field drains) are ideal drains, and some models do not include the water entrance resistance factor at pipe p...

New Approaches to Agricultural Land Drainage: A Review

A review on agricultural effects of restricted soil drainage conditions is presented, related to soil physical, chemical and biological properties, soil water availability to crops and its effects on crop development and yield, soil salinization hazards, and the differences on drainage design main objectives in soils under tropical and semi-arid water regime conditions. The extent and relative importance of restricted drainage conditions in Agriculture, due to poor irrigation management is discussed, and comprehensive studies for efficient drainage design and operation required are outlined, as related to data gathering, revision and analysis about geology, soil science, topography, wells, underground water dynamics under field conditions, the amount, intensity and frequency of precipitations, superficial flow over the area to be drained, climatic characteristics, irrigation management and the phenology of crop productive development stages. These studies enable determining areas affected by drainage restrictions, as well as defining the optimal drainage net design and performance, in order to sustain soil conditions suitable to crops development.

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).

Simulating Hydraulic Behavior of an Agricultural Drain Based on Experimental Data

AbstractSimulation models have been used in a limited fashion to describe and characterize soil water flow in saturated conditions as an approach to optimize drainage design parameters. The dynamic...

Modeling Agricultural Drainage Hydraulic Nets

A review on mathematical models available in the literature to design and evaluate agricultural drainage hydraulic nets is presented, including open ditch and buried pipe alternatives, for steady state and no steady state soil water flows, homogeneous and stratified soil profiles and smooth and corrugated drainage pipes. Effective drainage pipe radius effects on drainage performance is considered, based on its perforation density and distribution, as it affects pipe weight bearing strength and pipe deformation intensity. Also, quantitative considerations on perforation density upon water flow resistance into the drain pipe are analyzed.