A cytohistological analysis of roots whose growth is affected by a 60-Hz electric field

Roots of Pisum sativum were exposed for 48 h to 60-Hz electric fields of 430 V/m in an aqueous inorganic growth medium. The growth in length of the exposed roots was 44% of that for control roots. Root tips were analyzed for mitotic index and cell cycle duration. Mature, differentiated root sections from tissue produced after electrode energization were analyzed for cell lengths and number of files. The major reason for the observation that exposed roots are shorter than control roots is that cell elongation in the former is greatly diminished relative to controls.     

Growth rate and mitotic index analysis of Vicia faba L. roots exposed to 60-Hz electric fields

Growth, mitotic index, and growth rate recovery were determined for Vicia faba L. roots exposed to 60-Hz electric fields of 200, 290, and 360 V/m in an aqueous inorganic nutrient medium (conductivity 0.07-0.09 S/m). Root growth rate decreased in proportion to the increasing strength; the electric field threshold for a growth rate effect was about 230 V/m. The induced transmembrane potential at the threshold exposure was about 4-7 mV. The mitotic index was not affected by an electric field exposure sufficient to reduce root growth rate to about 35% of control. Root growth rate recovery from 31-96% of control occurred in 4 days after cessation of the 360 V/m exposure. The results support the postulate that the site of action of the applied electric fields is the cell membrane.     

On the mechanism of 60-Hz electric field induced effects inPisum sativum L. roots: Vertical field exposures

Roots of Pisum sativum L. were chronically exposed to 60-Hz vertical electric fields ranging from 150 to 450V/m in an aqueous medium whose conductivity was approximately 0.07 S/m. Control and exposed roots were grown concomitantly in the same tank whose medium was continuously circulated and maintained at 19 degrees C. The experiments were conducted blind. Root growth rates were determined daily and the mitotic index was determined for various intervals over a 24-h period, ranging from 12 h before to 12 h after electrode energization. Root growth rates were affected in a dose dependent relationship by exposures greater than 250 V/m. Mitotic indices were not affected by 150 V/m but were affected at 350 V/m; the former exposure did not alter root growth rates, the latter did. The growth rates of vertically exposed roots were compared to those of horizontally exposed roots; the former are more sensitive at a given field strength. The observations are consistent with the postulate that the electric field acts upon the cell through a perturbation of the transmembrane potential.     

60 Hz electric field parameters associated with the perturbation of a eukaryotic cell system

Summary Roots ofPisum sativum were exposed for seven days to 60 Hz electric fields ranging from 70–430 V/m in an aqueous medium whose conductivity was approximately 0.07 mho/m. (Corresponding current densities in the exposure medium associated with these field strengths ranged from 0.5–3.0 mA/cm²). Control and exposed roots were grown concomitantly in the same tank whose growth medium was continuously circulated. Temperature in the exposure medium was held at a constant 19° C. All experiments were conducted double blind. Root growth rates were determined daily. No perturbations in root growth were observed with electric fields of 150 V/m; there was a slight effect at 360 V/m, and a pronounced decrease in growth rate occurred at 430 V/m. Root conductivities are comparable to that of the growth medium. Under conditions in which growth inhibition occurs, it is estimated that induced 60 Hz cell membrane potentials would be of the order of 3–8 mV.     

The relationship between sensitivity to 60-Hz electric fields and induced transmembrane potentials in plants root cells

Summary Growth rates and cell diameters were determined from 12 species of plant roots exposed to a 60-Hertz (Hz) electric field of 360 Volts per meter (V/m) in an aqueous inorganic nutrient medium [conductivity: 0.07–0.09 Siemens per meter (S/m)]. The degree of growth depression ranged from zero to nearly 100 percent of control. Cell diameters ranged from 13.5 to 31.8 µm as an averaged value for procambial, cortical, and meristem cells. Sensitivity to the electric field as determined by root growth rate reduction increased with increasing cell size. Sensitivity also increased with increase in 60 Hz induced transmembrane potentials; the transmembrane potential threshold for growth reduction was about 6.0 mV and the potential for near-complete cessation of growth was about 10–11 mV.Two different hypothetical mechanisms of action by which applied electric fields induce biological effects at the cellular level were tested. The two mechanisms pertain to different possible modes of action of applied electric fields: one mechanism postulates the involvement of the transmembrane field, the other mechanism postulates the tangential electric field as the important factor for inducing biological effects. The data support the transmembrane and not the tangential field mechanism. It is concluded that the effects observed are consistent with a membrane related mechanism and that there is a narrow range (a few mV) between threshold and debilitating induced membrane potentials.     

Effects of sinusoidal 60-Hz electric and magnetic fields on ATP and oxygen levels in the slime mold, Physarum polycephalum

We have previously reported that exposing the vegetative plasmodia stage of Physarum polycephalum to either individual or simultaneously applied electric and magnetic fields (45-75 Hz, 0.14-2.0 G, and 0.035-0.7 V/m) lengthens their mitotic cycle, depresses their rate of reversible shuttle streaming, and lowers their respiration rate. In this article we report the effects of simultaneously applied electromagnetic fields (60 Hz, 1.0 G, 1.0 V/m), electric fields only (60 Hz, 1.0 V/m), magnetic fields only (60 Hz, 1.0 G) on the haploid amoeba of Physarum exposed for 120-180 days. Statistically significant depressions (about 8-11%) in ATP levels were observed with all field conditions; however, respiration was significantly decreased only when amoebae were subjected to either combined fields or electric fields alone. Magnetic fields alone failed to induce a significant decrease in respiration.     

On the mechanism of a 60-Hz electric field induced growth reduction of mammalian cellsin vitro

Data on 60-Hz electric field (EF) induced reduction in growth rate of plant roots have strongly supported the hypothesis that the effect is related to an EF-induced transmembrane potential (V ⁱ _m). An investigation was undertaken to determine if this hypothesis is also applicable to 60-Hz EF-induced reductions in growth rate of mammalian cells in vitro. Human lymphoblastic (RPMI 1788) and human carcinoma (HeLa) cells were selected for study, the former having a relatively small diameter (11.2 m), and the latter having a relatively large diameter (15.4 tm). The 60-Hz EFs ranged from 430–1200 V/m in the culture medium. The growth rate of RPMI 1788 cells after 4-days was depressed by about 42% at a 60-Hz EF of 1000–1200 V/m with a response threshold occurring at 950 V/m; theV ⁱ _m at the response threshold was 8 mV There was no 60-Hz EF-induced effect on HeLa cell growth rate of aV ⁱ _m of 8 mV (60-Hz EF=700 V/m); a statistically significant effect was achieved atV ⁱ _m of 11 mV (950 V/m). The data support the hypothesis that above a threshold 60-Hz EF,V ⁱ _m acts as the initial signal leading to growth rate reductions.     

Influence of 400, 900, and 1900 MHz electromagnetic fields on Lemna minor growth and peroxidase activity

Increased use of radio and microwave frequencies requires investigations of their effects on living organisms. Duckweed (Lemna minor L.) has been commonly used as a model plant for environmental monitoring. In the present study, duckweed growth and peroxidase activity was evaluated after exposure in a Gigahertz Transversal Electromagnetic (GTEM) cell to electric fields of frequencies 400, 900, and 1900 MHz. The growth of plants exposed for 2 h to the 23 V/m electric field of 900 MHz significantly decreased in comparison with the control, while an electric field of the same strength but at 400 MHz did not have such effect. A modulated field at 900 MHz strongly inhibited the growth, while at 400 MHz modulation did not influence the growth significantly. At both frequencies a longer exposure mostly decreased the growth and the highest electric field (390 V/m) strongly inhibited the growth. Exposure of plants to lower field strength (10 V/m) for 14 h caused significant decrease at 400 and 1900 MHz while 900 MHz did not influence the growth. Peroxidase activity in exposed plants varied, depending on the exposure characteristics. Observed changes were mostly small, except in plants exposed for 2 h to 41 V/m at 900 MHz where a significant increase (41%) was found. Our results suggest that investigated electromagnetic fields (EMFs) might influence plant growth and, to some extent, peroxidase activity. However, the effects of EMFs strongly depended on the characteristics of the field exposure.     

Influence of potassium ion and osomtic pressure on development of Haemonchus contortus in vitro.

Development of infective larvae of Haemonchus contortus to the fourth stage in vitro was impaired if the concentration of potassium ion in the medium was 0.26 mM or less. At or below 0.015 mM, development was almost completely stopped. High concentrations of potassium, in solutions with a ratio of sodium to potassium from 150 down to 1.3, were all equally favorable for development, but solutions composed only of salts of potassium were unfavorable. Development was impaired by osmotic pressures below 200 mosm/kg or above 350 mosm/kg and ecdysis was arrested by high but not by low osmotic pressures.     

Electrotropism of Maize (Zea mays L.) Roots (Facts and Artifacts)

Intact and decapped primary roots of maize (Zea mays L.) were exposed to DC electric fields of 0.5 to 8.0 V/cm in low-salinity media to resolve conflicting results about the direction of electrotropism. In DC fields of 0.5 V/cm or 1.0 V/cm, intact roots always curved toward the cathode. In a field of 8.0 V/cm, intact roots curved toward the anode and stopped growth. Decapped roots also curved toward the anode both in weak and strong fields. The results indicate that growth toward the cathode is the true response of healthy roots.     

二氧化硫衍生物对蚕豆幼苗生长和细胞周期的影响

研究SO₂体内衍生物NaHSO₃与Na₂SO₃(1:3,mmol/L)对蚕豆幼苗生长和细胞分裂的影响。结果表明:SO₂衍生物(浓度在0~30mmol/L)对幼苗生长的抑制作用具有剂量效应和时间效应关系,短时间处理效应不明显,处理48h后蚕豆幼根生长抑制,168h后幼苗根上部分长度(芽长)表现生长抑制,根长和芽长与处理浓度间呈负线性相关。SO₂衍生物处理12~36h,导致根尖细胞分裂指数下降,根尖中前期细胞减少,间期、后期和末期细胞增多,表明SO₂衍生物能够阻止细胞进入分裂态,延长分裂过程,这可能是SO₂衍生物处理组根尖细胞分裂指数降低,幼苗生长抑制的主要原因。     

Quick and reversible inhibition of soybean root nodule growth by nitrate involves a decrease in sucrose supply to nodules

The upper part of a nodulated soybean root hydroponically cultured in a glass bottle was monitored using a computer microscope under controlled environmental conditions, and the diameter of individual nodules was measured from 10-24 d after planting. The diameter of a root nodule attached to the primary root increased from 1 mm to 6 mm for 2 weeks under nitrogen-free conditions. The increase in diameter of the nodules was almost completely stopped after 1 d of supplying 5 mM nitrate, and was due to the cessation of nodule cell expansion. However, nodule growth quickly returned to the normal growth rate following withdrawal of nitrate from the solution. The reversible depression of nodule growth by nitrate was similar to the restriction of photoassimilate supply by continuous dark treatment for 2 d followed by normal light/dark conditions. In addition, the inhibitory effect of nitrate was partially alleviated by the addition of 3% (w/v) sucrose to the medium. Plant leaves were exposed to (11)C or (14)C-labelled carbon dioxide to investigate the effects of 5 mM nitrate on the translocation and distribution of photosynthates to nodules and roots. Supplying 5 mM nitrate stimulated the translocation rate and the distribution of labelled C in nitrate-fed parts of the roots. However, the (14)C partitioning to nodules decreased from 9% to 4% of total (14)C under conditions of 5 mM nitrate supply. These results indicate that the decrease in photoassimilate supply to nodules may be involved in the quick and reversible nitrate inhibition of soybean nodule growth.     

Short term cultivation of isolated barley roots and their mitotic activity

Roots were excised from barley embryos cultivated in the complete liquid nutrient solution and cultivated in the same nutrient solution separately. The excised roots continued their growth but a progressive decrease in the growth rate was observed. There was a considerable short-term drop of the mitotic activity immediately after excision, which was followed by a compensatory increase and then equilibrium was reached 12 h after excision. During the next at least three days, the mitotic index of isolated barley roots varied between 5–6.5%, which is slightly lower than the mitotic index of the root meristems of isolated barley embryos under identical conditions. The mitotic cycle index of isolated barley roots and the size of the root meristem later decreased gradually.     

Induction of ELF transmembrane potentials in relation to power-frequency electric field bioeffects in a plant root model system

Summary Seminal roots ofCucumis sativus andCucurbita maxima were exposed to 60 Hz electric fields of 100–500 Vm^–1 in a conducting aqueous inorganic growth medium. Root growth rates were measured to produce a dose-response relationship for each species. The species were selected for study because of their familial relationship, reported sensitivity to 60 Hz, 360 Vm^–1 electric fields, and differing average root cell sizes. The latter characteristic influences the magnitude of ELF membrane potentials induced by constant-strength applied electric fields, but does not affect the magnitude of the electric field strength tangent to the cell surface. The difference in average root cell size betweenC. sativus (smaller cells) andC. maxima (larger cells) was used to evaluate two alternate hypotheses that the observed effect on root growth is stimulated by [1] the electric field tangent to the cell surface, or (2) a field-induced perturbation in the normal transmembrane potential of the cells.The results of the dose-response relationship studies are qualitatively consistent with the hypothesis that the effect is elicited by induced transmembrane potentials. The smaller-celled roots showed a substantially higher response threshold [C. sativus; E ₀ ^TH 330 Vm^–1] than did the larger-celled species [C. maxima; E ₀ ^TH 200 Vm^–1]. At field strengths above the response thresholds in both species, the growth rate ofC. sativus roots was less affected than that ofC. maxima roots exposed to the same field strength.     

Priming of seeds with NaCl induces physiological changes in tomato plants grown under salt stress

The effects of seed priming with 6 M NaCl solution have been investigated with respect to growth and physiological responses of tomato plants ( Lycopersicon esculentum Mill. cv. Pera) exposed to 70 and 140 m M NaCl nutrient solutions from 11 to 60 days after sowing. Tomato seedlings from primed seeds emerged earlier than from non-primed seeds. At 70 m M , a lower shoot and root dry weight reduction was found in plants from primed seeds at the different harvests (30, 45 and 60 days after sowing), while at 140 m M the positive effect of seed priming was only shown in roots. Significant changes in Na⁺ and CI⁻ accumulation with seed priming were only found in roots at 60 days after sowing, with ion accumulation in roots being higher in plants grown at 70 and 140 m M from primed seeds. In leaves of salt-treated plants, significant increases in sugars and organic acids with seed priming were found from 30 days after sowing, and these increases were higher at longer treatment times. In roots, however, only the organic acids tended to increase in plants from primed seeds, although they increased less than in leaves, especially at 60 days after sowing. These results support the hypothesis that priming of seeds with NaCl induces physiological changes in the plants, changes which are shown more clearly at advanced growth stages.     

CELL CYCLE COMPARTMENT ANALYSIS OF CHINESE HAMSTER CELLS IN STATIONARY PHASE CULTURES

The distribution of Chinese hamster cells with respect to the compartments of the cell generation cycle was studied in cultures in the stationary phase of growth in two different media. A measure of the state of depletion of the nutrient medium was formulated by defining a quantity termed the nutritive capacity of the medium. This quantity was used to verify that the cessation of cell proliferation is due to nutrient deficiencies and not to density dependent growth inhibition. Cell cultures in stationary phase were diluted into fresh medium and as growth resumed, mitotic index, cumulative mitotic index, label index and viability were measured as a function of time. The distribution of cells with respect to compartments of the cell generation cycle in stationary phase populations was reconstructed from these data. Stationary phase populations of Chinese hamster cells that retained the capacity for renewed growth when diluted into fresh medium were found to be arrested in the G₁ and G₂ portions of the cycle; the relative proportion of these cells in G₁ increased with time in the stationary phase, but the sequence differs in the two media. In early stationary phase, in the less rich medium, more cells are in G₂ than in G₁. Also in this medium a fraction of the population was observed to be synthesizing DNA during stationary phase, but this fraction was not stimulated to renewed growth by dilution into fresh medium.     

Effect of static electric fields in root cells of Vicia faba (Fabaceae)

Serial electron microscopic sections were prepared from half-ripened meristematic root cells of Vicia faba (Fabaceae) which had been exposed gradually to 700, 1000, 2500, 3500, and 5000 V/m static electric fields during seven days with and without Zn and Cd electrodes. At the end of five weeks, wall loosenings and very small nuclei were observed in those root cells which were exposed to static electric currents from the lower side of the medium without electrodes, while abnormalities in cell formation, e.g., two cells with one nucleus, and GER occurrence were present in an electrolytic (Cd upward and Zn downward) medium. The cells exposed to a static current from the upper side of the medium had small nuclei and abnormal cell divisions in the electrolyte, but in a non-electrolyte very large nuclei and thicker cell walls were observed, the cytoplasm was dense with GER, pinocytosis was seen filled with mitochondria, and protoplast formation with big nuclei was seen in exocytosis.     

Cell cycle modulation in the response of the primary root of Arabidopsis to salt stress

Salt stress inhibits plant growth and development. We investigated the importance of cell cycle regulation in mediating the primary root growth response of Arabidopsis to salt stress. When seedlings were transferred to media with increasing concentrations of NaCl, root growth rate was progressively reduced. At day 3 after transfer of seedlings to growth medium containing 0.5% NaCl the primary roots grew at a constant rate well below that prior to the transfer, whereas those transferred to control medium kept accelerating. Kinematic analysis revealed that the growth reduction of the stressed roots was due to a decrease in cell production and a smaller mature cell length. Surprisingly, average cell cycle duration was not affected. Hence, the reduced cell production was due to a smaller number of dividing cells, i.e. a meristem size reduction. To analyze the mechanism of meristem size adaptation prior to day 3, we investigated the short-term cell cycle events following transfer to saline medium. Directly after transfer cyclin-dependent kinase (CDK) activity and CYCB1;2 promoter activity were transiently reduced. Because protein levels of both CDKA;1 and CDKB1;1 were not affected, the temporary inhibition of mitotic activity that allows adaptation to the stress condition is most likely mediated by posttranslational control of CDK activity. Thus, the adaptation to salt stress involves two phases: first, a rapid transient inhibition of the cell cycle that results in fewer cells remaining in the meristem. When the meristem reaches the appropriate size for the given conditions, cell cycle duration returns to its default.     

Interrelationship between the growth rate of wheat roots,their excretory activity,and the number of border cells

Excretion of proteins and carbohydrates, the number of root border cells (BC), and the effect of different concentrations of NaF (1, 5, 10, and 20 mM) on the growth rate of the roots were investigated in the seedlings of wheat (Triticum aestivum L.) with low (LGR) and high growth rate (HGR). At the early stage of growth (1 day), the rate of protein excretion to the medium was much greater in the LGR roots; as to carbohydrates, the difference between the LGR and HGR roots was less pronounced. When added to the germination medium, NaF suppressed root growth and induced excretion of high-molecular-weight proteins into the medium; this phenomenon was more pronounced in the HGR-roots. The number of BC did not depend on the rate of protein excretion into the medium. The population of BC was the same in the HGR and LGR roots. When 1 mM NaF was added to the medium, the number of BC in the rhizosphere equally increased in both HGR and LGR roots. The elevation of NaF concentration did not affect the number of BC.     

Influence of airborne suspended matter on mitotic cell division

The effect of organic extracts of airborne suspended matter collected in the highly polluted industrial region of Silesia (Poland) on mitotic cell division was evaluated in the Chinese hamster V79 cell line. Crude benzene extracts as well as sequential elution solvent chromatography (SESC) fractions were investigated for their ability to affect the mitotic index, the proportion of anaphases-telophases to metaphases (AT/M ratio), the cloning efficiency and to produce aneuploid cells. The incidence of cell division disturbances in V79 cells exposed to extracts increased in a concentration-dependent manner. Mitotic arrest, manifested as a highly increased mitotic index and a concomitant decrease in the AT/M ratio, was found for the crude extract at a dose corresponding to 0.75 m3 of air. Comparable effects were noticed for SESC fraction 4, probably containing monophenol compounds. A strong dose-dependent reduction of cloning efficiency of V79 cells demonstrated cytotoxic activity of both the crude extract and fraction 4.