The problem of giant cells in biology.
The influence of geomagnetic field (GMF) outbursts on the cellular structure of root apices of Allium cepa L. was established. The tips of roots and shoots were fixed twice per day during a 24-day period. Abnormal binuclear, tetranuclear cells, large cells with large nuclei, and giant cells with giant nuclei were observed in the meristem zones of the root apices. They were surrounded by mononuclear diploid cells. Within some days of the experiment, the amount of polynuclear cells comprised as much as 20% of all the meristem cells. The graphical presentation of this process shows peaks and troughs in the number of polynuclear cells. By comparing this with the changes in the GMF characteristics at the same days, we found a striking correlation between the two. The in vitro experiments on isolated root tip meristems allowed us to exclude the possibility of centralized regulation of cell structure changes being affected by the mutual exchange of metabolites between organs of the whole plant. The artificial screening of the GMF led to a significant decrease of cells with enhanced nuclear DNA content. The same plant cells demonstrated greater sensitivity to fluctuation of GMF under geographical conditions of high-latitude.
It is well known that plant development is determined mainly by the functional activity of the meristems. Meristems are the most sensitive tissues that form the plant body. The sustainability of the meristems determines the resistance of the whole plant to harmful influences from the environment. (1) In our publications, we have shown that the cell structure of the root meristem of Allium cepa L. and several species of Triticum L. can be changed under the influence of the geomagnetic field (GMF). (2,3,4,5) On particular days, the peak values, phases, and periods of oscillations (frequencies) of GMF constantly vary. During the periods of sharp GMF outbursts- called magnetic storms, the polynuclear cells, large cells with large nuclei and giant cells with giant nuclei appear among the regular meristematic cells. The appearance of these cells is initiated suddenly and continues during two-three days. Usually polynuclear, these large and giant cells appear distributed as single cells. These new cells are not organized in strings or clusters. They do not become the initiators of gistogenesis. Polynuclear, large and giant cells are absent in the areas of the absorption zone of the root. In some large and giant cells, we observed the fragmentation and disintegration of the nuclei.
Production of cells with enhanced DNA content, or endo-reproduction, takes place in differentiated and functionally active tissues of plants and animals. (6,7) In our experiments, we confirmed the appearance of such giant cells in primary meristems of the zone of cell division in the root, where the cell differentiation did not take place. We demonstrated for the first time the primary role of the GMF in the initiation of the giant cells. This observation indicates the fundamental importance of the study of plant giant cell production under the influence of GMF. Results of our investigation in this field during the period from 1991 until 2002 are explained in 25 publications, mainly in Russian.
2. Cosmic Factors and Plant Adaptation
Our studies have shown that the cause of the appearance of giant cells is the fluctuations of the GMF that takes place under the influence of solar activity. It was to test the influence of the varying GMF on changes of cell structure of apical meristems that these cytology experiments were conducted. Seeds of onion Allium cepa L. were soaked in water and germinated in darkness for three-five days. The seedling root tips were fixed daily through the period of one month, stained with acetocarmine and squashed preparations prepared. This experiment has been reproduced several times in different years. The advantage of squashed preparations is the positioning of all cells in a monolayer and the distribution of chromosomes in one plane without overlapping. This is very important for the observation of very apical areas of root tips called meristems, where cells permanently divide and respond to GMF fluctuations. This allows us to measure operatively the quantity of DNA at once in all chromosomes in the metaphase plate and in the whole nucleus. By changing the degree of the maceration and orientation of the tissue on a glass slide during microscopy observation, it is possible to obtain preparations where particular tissue layers and cell allignments, organ zonation, the cells themselves, and the cell contents are clearly visible. The numbers of bi- and tetra-nuclear cells as a percentage of the total cell numbers in the preparation was plotted on the left ordinate. The Planetary Index of Geomagnetic Perturbation Kp was plotted on the right ordinate. It ranged from zero to nine, depending on the amplitude of GMF oscillations and was recorded eight times per day at three-hourly intervals. The information about the GMF fluctuations during the periods of our experiments was provided by The World Solar and Terrestrial Physics Database, Russian Academy of Sciences, Moscow.
Daily total microscopy analysis of preparations during each of one-month experiments revealed appearance of binuclear and tetranuclear cells that composed up to 20% of all cell number of root apices during outbursts of GMF (Figure 1a).
[FIGURE 1 OMITTED]
During three-four days after magnetic storm, the number of binuclear and tetra-nuclear cells decreased and the number of large cells with big nuclei increased (Figure 1b). Then, the number of large cells decreased and giant cells with giant nuclei appeared (Figure 1c). We have observed 8-17 giant cells with giant nuclei in each preparation. During four-five "calm" days after a magnetic storm, multinuclear, large and giant cells disappeared and regular diploid meristem cells were observed. After a certain period of time, the entire situation repeated with the same sequence of events. We concluded that the dynamics of the development of cell transformations that we observed in our experiments is characterized by sustainability.
Changes of the number of polynuclear cells as the function of days of fixation are described graphically as a curve with peaks and gaps. During comparison of this curve with average day fluctuations of GMF, we discovered the complete coincidence of two of these effects (Fig. 2).
[FIGURE 2 OMITTED]
To answer the question whether the regulation of adaptive changes that we observed in our experiments is dependent on whole plant organism, we conducted special experiments with sterile isolated root apices that had been cultivated on the surface of artificial agar medium. The dynamics of cell structure changes in isolated roots is the same as in seedling roots. This observation indicates the lack of centralized hormonal regulation of cell structure changes in root apical meristems.
3. Permalloy Shielding
To identify the influence of magnetic storms, we germinated the onion seeds and incubated the seedling roots during three-five days in darkness under the protection of a permalloy shield manufactured from an alloy of nickel and iron that reduces the GMF strength. In shielded root apical meristems, the numbers of poly-nuclear, large, and giant cells were significantly reduced in comparison with control meristems incubated without shielding. These results support the fact of plant geomagnetic reception. It is known that continuous shielding (hypomagnetic milieu) leads to a reduction of proliferative activity of formative tissues and functional genome activity in all studied plants. (8) These data provide evidence for the importance of the magnetic field of the Earth as one of the global factors necessary for normal plant growth and development.
Polyploid cells with increased DNA content usually appear in differentiated and functionally active tissues. The appearance of these cells in non-differentiated meristem tissues probably can be considered as an adaptive reaction to changes of the Earth's magnetic field. (2,3,4) Stress reaction to GMF exposure leads to loss of sustainable state by the system and causes the system to search for new states that might be expressed in cell transformation. This is supported by studies in which it was shown that at the cellular level, the action of the GMF might be realized through nonspecific change of cell membrane polarization and permeability. (9,10) Initiation and synchronization of a variety of cellular processes are closely connected with the fluctuations of GMF. It was shown that the magnetic field of the Earth influenced the mechanisms of membrane permeability and might control sustainability of the genetic systems and processes, and initiate their cyclic changes. (11,12)
The change of cell membrane permeability is one of the manifestations of plant reactions to an environmental stress influence. The permeability of the plasmalemma for electrolytes is the integral characteristic of the functional state of plants during the stresses. During magnetic field storms, apparently not only do the cell membranes change their permeability, but the process of membrane formation might be modified resulting in cell structure change.13 Our data can be accounted for by the interaction of natural low-frequency electromagnetic fields with endogenous cellular fields that leads to further change of cell structure. (14)
In considering the interrelations of GMF with homeostasis of biological systems, it is necessary to take into account that living organisms have their own fields, which are composed of complex interactions of fields at all organizational levels of living matter starting with the sub-atomic level. Each cell possesses its own fields and selectively responds to frequency characteristics of geophysical fields. The GMF comprises stationary and variable components. The period of change in the stationary GMF of the Earth amounts to hundreds of years. The variable GMF changes are within the periods ranging from the fractions of seconds to several months. The value of the variable GMF does not exceed 2% of the static GMF, yet its biological role is very significant. The cell is a rhythmic oscillatory system. At the same time, the cell is an emitter and receiver of electromagnetic fields. Thus, the regularities of synchronization and resonance might be applied to the living cell. The greatest effect of the GMF might be observed during the appearance of the resonance processes. The experimental observations that magnetic fields with strength equal to GMF, or lower in some cases, produce greater biological effects than magnetic fields with high and superhigh strength might be accounted for by resonance interactions.15 In spite of low intensity, natural magnetic fields express fundamental influence on physiological activity of all living organisms. Variable biological responses to the GMF are also due to the magnetic field orientation.10 Another important feature of the GMF is the continuity of its action everywhere during long periods of time. (15)
4. The Effects of Latitude
Along with universal action of the GMF, which can be considered as the general space and time coordinate for living organisms, another interesting characteristic of the GMF is the variety of the reactions of biological systems to GMF. Geomagnetic storms represent a significant stress-generating factor, which initiates a large set of adaptive reactions in living organisms. In accordance with the theory of academician Vernadsky, the Earth sphere represents for the planet Earth a geological formation, the product of astrophysical, physical and chemical processes continuing during billions of the years. Geological and geochemical analysis of the processes taking place at the Earth's surface is impossible without taking into account interaction between living nature and lifeless nature. (16) Russian Near-Pole and Far-North regions might be considered a unique laboratory, where the influence of geomagnetic fluctuations on bio-systems is much more significant than in Central Russia, due to particularities of geo-sphere and bio-sphere interactions. These particularities are determined by the influence of solar activity and the dependence of GMF on latitude. Thus, at the North magnetic pole, the strength of Earth's magnetic field is 0.6 Oe, at the South magnetic pole 0.7 Oe, at the magnetic equator 0.35 Oe. (11) It is in the area of high latitude that interaction of solar corpuscular and wave irradiations with the system magnetosphere-ionosphere-atmosphere-Earth leads to the most intense and diverse effects of electromagnetic field variations on living organisms. (11,12)
The electromagnetic background in polar regions is particularly important as the environmental factor due to generation of polar tension syndrome, a special regime of functioning of adaptive mechanisms of the organism. (17) Polar tension syndrome is the accumulation of fatigue in bio-systems under the environmental pressure of extreme conditions of high latitude. GMF in polar regions could be considered as a stress factor involved in generation of pre-morbid states of living organisms. 17 At all latitudes of the Earth, the geomagnetic storms more or less negatively influence human health. They negatively affect almost all systems of the organism-nervous, endocrine, cardiovascular, and blood generation. During the maximum geomagnetic activity, the viscosity of blood increases, the aggregation of erythrocytes and thrombocytes enforces. At the cellular level, during enhanced geomagnetic outbursts, in preparations of in vitro cultures of human blood cells, the giant cells and poly-nuclear cells were present. (18) The normalization of blood cell characteristics takes place only on the third day after the peak of a magnetic outburst. (17)
The viability of biosystems in Northern latitudes is determined by their resistance to significant fluctuations of natural factors of environment, including the variations of GMF. To elucidate the type of adaptive reactions and degree of realization of adaptive potential of biosystems at different geographical latitudes, we conducted the set of parallel experiments during which we analyzed the cytological structure of apical meristems of Allium cepa L., which we have chosen as the model system.
Root apices was fixed at the same time twice a day, every day, during the period of 24 days in Moscow (55.7 N; 37.8 E) and on Srednii island in the White Sea (66.3 N; 33.7 E). Root apical meristems were stained with acetocarmine. Then, squashed cytological preparations of root meristem tips were analyzed. If we present our data graphically, showing the number of cells with enlarged genome on the Y-axis and days of fixation in Moscow and on the White Sea on X-axis, we obtain curves with coinciding peaks and troughs. However, the amplitude of cell response was greater on the White Sea than in Moscow, which is consistent, because the GMF fluctuations are more intense in North region (Figure 2).
Researchers consider the appearance of giant cells to be an adaptive reaction of biosystems to changes of environmental factors. (1,19,20) These authors explain this phenomenon with the hypothesis that the genetic protection of polyploids is provided by increasing the number of repeated genomes. This process eliminates chromosome aberrations that might appear at one genome. Increasing of ploidy in cell populations is one of the universal reactions that develop in response to destructive influence of environment and is aimed at the preservation of sustainability that is crucial to system viability. Living organisms and cells, which are affected by different environmental factors, including GMF, apparently developed compensative mechanisms of adaptation to this factor. Low-energy magnetic fields, such as the GMF, might influence the adaptive cell processes. Cells as biological systems possess the capability of adaptation to environmental factors. Ontogenesis of large and giant cells, in accordance with our observations, is terminated by fragmentation and decay of nuclear DNA. We propose the hypothesis that during stress situations, such as magnetic storms, the giant nuclei are formed as compensative structures. Later, the giant nuclei are fragmented and disintegrate. Then, neighboring cells absorb the nuclear material together with other organelles of giant cells. This plays a role during the process of utilization of assimilates and could be viewed as "endogenous nutrition." Similar processes have been observed in animal cell cultures in vitro. Thus, genetically programmed death of the cell-apoptosis-appears as a necessary process to support the homeostasis of an organism during a stress situation. The morphogenetic and adaptive role of apoptosis was demonstrated by Voeikov. (21)
In conclusion, we can say that during environmental influences that exceed the level of tolerance, the cells pass to another functional level as a whole system. The structural and functional changes that we observe during this process are aimed at the preservation of the living system, i.e., these changes possess adaptive characteristics.
Resulting from the study of squashed preparations during many years, we have established changes in apical meristems of Allium cepa L. These changes include the appearance of poly-nuclear and giant cells. We have studied the dynamics of this process. The lack of centralized regulation of observed phenomenon is confirmed experimentally. We show for the first time that these changes are synchronous to fluctuations of the magnetic field of the Earth.
On the basis of our conducted studies, we can make the following conclusions.
1) The plant cells possess a capability for geo-magneto-reception. Under the influence of external factors (GMF fluctuations), noncentralized cell self-regulation takes place in plant meristems.
2) Under the extreme environmental conditions in Northern latitudes, biosystems are affected by intense fluctuations of geomagnetic fields (magnetic storms) and have to express higher adaptive potential to preserve their own viability.
We thank Professor A. P. Dubrov for fruitful discussions on the role of geomagnetic field (GMF) in cell functioning and for help during manuscript preparation.
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E. R. Nanushyan, A.Y. Skripnikov, V.V. Murashov
Lomonosow Moscow State University, Laboratory of Plant Development Biology,
Leninskie Gory 1-12, GSP-2, Moscow, 119992, Russia
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|Author:||Nanushyan, E.R.; Skripnikov, A.Y.; Murashov, V.V.|
|Date:||Sep 22, 2004|
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