![]() ![]() Impedance measures are used in various ways, including respiratory breathing rates with expansion and relaxation of a chest for mammals, the movements of a respiratory organ in crayfish to control aeration of gills, clinical neuromuscular diseases in mammals, heart rate of crustaceans submerged in water, as well as to detect when the environment causes physiological stress of crayfish, crab or shrimp. However, two leads are used to detect a change in resistance while passing a current. ![]() Thus, a Faraday cage is commonly used for such recordings to shield the environmental electrical noise.Īn impedance measure is similar to the differential recording mentioned above in that two leads are used to detect a change in the voltage. This configuration for differential recording is susceptible to field potentials in the environment, such as 50 (Europe) or 60 (North America) Hz frequency from electronic equipment. KCl is a good electrolyte for detecting voltage differences across compartments and across cell walls or membranes. For recordings within compartments and within cells of plants, a common practice is to use 0.3 or 0.1 M KCl within the recording glass microcapillary. In this procedure, the microcapillary is filled with a conductive media, such as 3 M KCl or potassium acetate as typically used for recordings across cell membranes in animal tissue. A high resistance recording lead can be obtained by coating the lead with an insulator, while leaving a small amount of wire exposed at the tip, or placing the recording lead with more surface exposure within a glass microcapillary, which has a small tip opening to the media being measured. Thus, having a small area of contact with the field being measured leads to a high resistance, and allows for small changes in current leading to a larger voltage change as established by Ohm’s law. If both the ground and recording leads are immersed within a solution with a large surface exposure on the recording lead, then a low resistance input will result. The standard differential electrical measure detects a voltage change from a ground lead to a recording lead however, if the recording lead does not have a high enough resistance, then small changes in the recording field are hard to detect. An impedance converter provides a steady current between two leads and if there is a change in the resistance between the leads, due to changes in ionic movement within the plant, a change in the resistance is detected and relayed as an alteration in voltage, which can be detected. ![]() ![]() Impedance measure in which the current is altered requires additional instrumentation to vary the current however, an impedance converter measures the correlated impedance changes. Impedance measures have been used in plants to detect changes in the environment which affects physiology. Impedance measures can detect electrical responses within a plant and are not as sensitive to field potentials in the environment. The use of intracellular recording with glass electrodes and amplification is sensitive to field potentials and requires cumbersome equipment that limits portability. The standard method to measure an electrical response in plants is to detect voltage changes with similar approaches used for detecting electrical changes across animal cells by intracellular recording techniques. The purpose of this report is to illustrate the ease in using impedance measures for monitoring electrical signals from individual plants or aggregates of plants for potentially scaling for high throughput and monitoring controlled culturing and outdoor field environments. Monitoring electrical activity in a plant that arises in a distant plant was also demonstrated using the impedance method. The impedance measures were performed in 5 different plants (tomato, eggplant, pepper, liverwort, and Coleus scutellarioides), and responses to mechanical movement of the plant, as well as injury, were recorded. Impedance measurements are able to detect injury in plants as well as exposure of the roots to environmental compounds (glutamate). An impedance measure using stainless steel wires is not as susceptible to electrically induced noises. This method is more susceptible to artifacts of equipment noise and photoelectric effects than an impedance measure. One method uses KCl-filled glass electrodes placed into the plant, similar to recording membrane/cell potentials in animal tissues. Commonly, a differential electrode recording between silver wire leads with the reference wire connected to the soil, or a part of the plant, is used. Electrical activity is widely used for assessing a plant’s response to an injury or environmental stimulus. ![]()
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