Electrical impedance spectroscopy (EIS) is a useful tool for the investigation of the structural characteristics of solid materials and also biological tissues. The structural changes in plant or animal tissues reflect the physiological state of the organism. Electrical impedance measurement seems to be applicable both for analytical and research laboratories, since once a stress or a quality trait is correlated with an impedance parameter the method is quick and safe for further analysis of great number of samples. This work attempted to explore the current state of literature in terms of the application of EIS that has already been done on animal and plant tissues, and more specifically searching for the possibility of wider future applicability in plant stress detection.

A b s t r a c t. Importance of phase angle measurement during the application of electrical impedance spectroscopy was studied by executing pot experiments with maize. Electrical impedance, phase angle (strength of capacitive character), and dissipation factor in the plant-soil system were scanned between 100 and 10 000 Hz current frequency. The frequency-dependent change in the phase angle could be described by optimum curves culminating within 920-3 650 Hz. Since the rate of energy dissipation is independent of root extent, the higher phase angle and lower energy dissipation were associated with the higher coefficient of determination achieved for the root electrical impedance -root system size (root dry mass and root surface area) regressions. The characteristic frequency selected on the basis of phase angle spectra provided a higher significance level at statistical comparison of plant groups subjected to stress conditions influencing root development. Due to the physicochemical changes observable in aging root tissue, the apex of phase angle spectra, thus the characteristic frequency, shifted continuously toward the higher frequencies over time. Consequently, the regularly repeated phase angle measurement is advisable in time-course studies for effective application of the electrical impedance method, and the systematic operation at the same frequency without determination of phase angle spectra should be avoided.K e y w o r d s: dissipation factor, root capacitance, electrical impedance spectroscopy, phase angle, root surface area INTRODUCTIONDestructive root investigation methods, such as soil cores, in-growth cores, or monoliths are unsuitable for continuous monitoring of root development or activity in response to changing environmental conditions. The applicability of the non-destructive ground penetrating radar, radioactive tracers, MRI or X-ray imaging techniques is also strongly limited in many cases: providing little resolution of root structure (detect clearly coarse roots only), these methods are not adapted for quantification of root surface area and examination of many plant phenomena related to root development (Cao et al., 2010;Èermák et al., 2006). Conversely, electrical impedance (EI) and electrical capacitance (EC) measurements in a plant-soil system offer good opportunities of rapid in situ investigation of the root system size and root activity without any intrusion into plant life function. By fixing an electrode at the plant stem and embedding the other one in the soil and connecting them by an LCR-instrument, the measured root EI and EC are directly correlated with root mass, root length, or root surface area (Chloupek, 1972;Ozier-Lafontaine and Bajazet, 2005;Rajkai et al., 2002). EI and EC methods have been used for investigation of detached plant tissues and organs subjected to various stress conditions (cold acclimation, freeze-thaw injury, drought, nutrient deficiency, or pathogen infection) as well as for studying intact root systems of plants cultivated in soil or grown in hydro...

A b s t r a c t. Electrical properties of food materials can give information about the inner structure and physiological state of biological tissues. Generally, the process of drying of fruits and vegetables is followed by weight loss. The aim of this study was to measure the impedance spectra of carrot slices during drying and to correlate impedance parameters to moisture content in different drying periods. Cylindrical slices were cut out from the carrot root along the axis. The slices were dried in a Venticell 111 air oven at 50°C. The weight of the slices was measured with a Denver SI-603 electronic analytical and precision balance. The weighing of the samples was performed every 30 min at the beginning of drying and every 60 min after the process. The moisture content of the samples was calculated on wet basis. The magnitude and phase angle of electrical impedance of the slices were measured with HP 4284A and 4285A precision LCR meters in the frequency range from 30 Hz to 1 MHz and from 75 kHz to 30 MHz, respectively, at voltage 1 V. The impedance measurement was performed after weighting. The change in the magnitude of impedance during drying showed a good correlation with the change in the moisture content.

16Background and aims The measurement of electrical capacitance in root-soil system (C R ) is a useful method for

The electrical impedance spectra of Jonathan apples exposed to different pressing force were measured in the frequency range from 1 kHz to 1 MHz with an HP 4284A precision RLC meter. The apoplasmic resistance (Ra), the symplasmic resistance (Rs), and the Ra/Rs ratio were determined as a function of the force and the deformation. Below the bioyield deformation, there was no observable change in the value of Ra/Rs. Above the bioyield, the Ra/Rs ratio markedly decreased in consequence of the Ra decrease due to both the increased ion concentration in the apoplasmic part and the decrease of cell membrane resistance as a result of cell membrane rupture.