Electrolyte leakage accompanies plant response to stresses, such as salinity, pathogen attack, drought, heavy metals, hyperthermia, and hypothermia; however, the mechanism and physiological role of this phenomenon have only recently been clarified. Accumulating evidence shows that electrolyte leakage is mainly related to K + efflux from plant cells, which is mediated by plasma membrane cation conductances. Recent studies have demonstrated that these conductances include components with different kinetics of activation and cation selectivity. Most probably they are encoded by GORK, SKOR, and annexin genes. Hypothetically, cyclic nucleotide-gated channels and ionotropic glutamate receptors can also be involved. The stress-induced electrolyte leakage is usually accompanied by accumulation of reactive oxygen species (ROS) and often results in programmed cell death (PCD). Recent data strongly suggest that these reactions are linked to each other. ROS have been shown to activate GORK, SKOR, and annexins. ROSactivated K + efflux through GORK channels results in dramatic K + loss from plant cells, which stimulates proteases and endonucleases, and promotes PCD. This mechanism is likely to trigger plant PCD under severe stress. However, in moderate stress conditions, K + efflux could play an essential role as a ‘metabolic switch’ in anabolic reactions, stimulating catabolic processes and saving ‘metabolic’ energy for adaptation and repair needs.

/pdf/stress-induced-electrolyte-leakage-the-role-of-k-permeable-57k80417ni.pdf

Stress-induced electrolyte leakage: the role of K+-permeable channels and involvement in programmed cell death and metabolic adjustment

Electrical properties of tissues, macromolecular solutions, and cell membranes are summarized at frequencies from the extra low frequency (ELF) to microwave range. Previously presented dielectric data are supplemented by new results and a more detailed discussion of the physical mechanisms for the observed temperature coefficients of the dielectric properties. The dielectric data are discussed in terms of the interaction mechanisms which give rise to observed relaxational effects. Possible mechanisms for nonthermal weak interactions between radio-frequency (RF) energy and tissues are discussed and evaluated.

RF-field interactions with biological systems: Electrical properties and biophysical mechanisms

In a preliminary report, Dexter, Tottingham and Graber (3) have described a method of estimating the hardiness of plants as applied to three varieties of alfalfa, in which exosmosis of electrolytes from suitably frozen tissue into distilled water is determined electrometrically, and the magnitude of the electrical conductivity associated with the known hardiness of the samples. They found a progressive hardening of Grimm alfalfa, a hardy variety, as the winter season approached, and little or no hardening in a very tender strain, Hairy Peruvian. Utah Common alfalfa was intermediate in response. The principle of increased permeability and electrical conductivity of injured tissue is a familiar one in plant physiology, while the method of electrical conductance as a measure of changing electrolyte concentration has been more or less standard for many years. (See Osterhout (16) ; Dixon and Atkins (4) ; Hoagland and Davis (9) ; Hibbard and Miller (6) ; Hottes and Huelsen (10) ; Pantanelli (17) ; Merrill (13) ; Stiles and J0RGENSON (21).) In the papers listed above the principle has been applied to injuries resulting from freezing, from the action of various chemicals, from pathological causes, and from mechanical rupture. In view of the fact that the chemical and physical theories of winterhardiness of plants have been amply discussed in recent publications, and since the bibliography has been so fully covered there, the consideration of this phase of the problem will be dismissed by reference to several papers which furnish suggestive discussions and inclusive citations of the literature. Maximow (12) has reviewed the various physical and chemical studies of the hardiness problem in which compositional or osmotic and colloidal properties of plants are shown to be associated with hardiness. He cites, as well, numerous recent investigations in which growth recovery from controlled freezing treatment is used to estimate the degree of hardiness. Newton (15), Weimer (22), Steinmetz (20), Rosa (18) and Chandler (2) present excellent discussions, full bibliographies and additional data in regard to several chemical and physical methods of investigating the hardiness of plants. It may be stated briefly that most, if not all, of the theories of winter-hardiness are built around the idea of the water-relations of the plant, and that structural, osmotic or colloidal pro-

Investigations of the hardiness of plants by measurement of electrical conductivity

The toxicity of zinc compounds to aquatic animals is modified by several environmental factors, particularly the hardness of the dilution water, the dissolved oxygen concentration, and temperature. The resistance of aquatic animals to zinc poisoning varies with species. It is modified by acclimatization, and possibly by age. Survival time is inversely proportional to concentration of zinc. For these reasons concentrations reported as lethal have varied widely. The nmode of toxic action of zinc is uncertain. At acutely toxic concentrations it probably kills fish by destroying gill tissues. At chronically toxic levels it may induce stress resulting in death. The action of zinc undoubtedly differs at different concentrations, it varies with life history, and it is non-specific.

Winthrop John Van Leuven Osterhout

Papers

Injury, Recovery, and Death, in Relation to Conductivity and Permeability