Plant Responses to Electromagnetic Fields

Authored by: Massimo E. Maffei

Biological and Medical Aspects of Electromagnetic Fields

Print publication date:  November  2018
Online publication date:  November  2018

Print ISBN: 9781138735262
eBook ISBN: 9781315186641
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During evolution, all living organisms experienced the action of the Earth’s magnetic field (MF) (also called geomagnetic field, GMF), which is a natural component of the environment. GMF is steadily acting on living systems, and influences many biological processes. There are significant local differences in the strength and direction of the GMF. For instance, at the surface of the Earth, the vertical component is maximal at the magnetic pole, amounting to about 67 µT and is zero at the magnetic equator. The horizontal component is maximal at the magnetic equator, about 33 µT, and is zero at the magnetic poles (Kobayashi et al., 2004). The MF strength at the Earth’s surface ranges from less than 30 µT in an area including most of South America and South Africa (the so-called south Atlantic anomaly) to almost 70 µT around the magnetic poles in northern Canada and southern Australia and in part of Siberia (Maffei, 2014; Occhipinti et al., 2014; Bertea et al., 2015). Most of the magnetic field observed at the Earth’s surface has an internal origin. It is mainly produced by the dynamo action of turbulent flows in the fluid metallic outer core of the planet, while little is due to external magnetic fields located in the ionosphere and the magnetosphere (Qamili et al., 2013). The GMF, through the magnetosphere, protects the Earth, together with its biosphere, from the solar wind deflecting most of its charged particles (Maffei, 2014).

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Plant Responses to Electromagnetic Fields

3.1  Introduction

During evolution, all living organisms experienced the action of the Earth’s magnetic field (MF) (also called geomagnetic field, GMF), which is a natural component of the environment. GMF is steadily acting on living systems, and influences many biological processes. There are significant local differences in the strength and direction of the GMF. For instance, at the surface of the Earth, the vertical component is maximal at the magnetic pole, amounting to about 67 µT and is zero at the magnetic equator. The horizontal component is maximal at the magnetic equator, about 33 µT, and is zero at the magnetic poles (Kobayashi et al., 2004). The MF strength at the Earth’s surface ranges from less than 30 µT in an area including most of South America and South Africa (the so-called south Atlantic anomaly) to almost 70 µT around the magnetic poles in northern Canada and southern Australia and in part of Siberia (Maffei, 2014; Occhipinti et al., 2014; Bertea et al., 2015). Most of the magnetic field observed at the Earth’s surface has an internal origin. It is mainly produced by the dynamo action of turbulent flows in the fluid metallic outer core of the planet, while little is due to external magnetic fields located in the ionosphere and the magnetosphere (Qamili et al., 2013). The GMF, through the magnetosphere, protects the Earth, together with its biosphere, from the solar wind deflecting most of its charged particles (Maffei, 2014).

The literature related to MF effects on living systems contains a plethora of contradictory reports, few successful independent replication studies, and a dearth of plausible biophysical interaction mechanisms. Most such investigations have been unsystematic, devoid of testable theoretical predictions and, ultimately, unconvincing (Harris et al., 2009). The progress and status of research on the effect of magnetic field on plant life have been reviewed in the past years (Phirke et al., 1996; Abe et al., 1997; Volpe, 2003; Belyavskaya, 2004; Bittl and Weber, 2005; Galland and Pazur, 2005; Minorsky, 2007; Vanderstraeten and Burda, 2012; Maffei, 2014; Occhipinti et al., 2014; Teixeira da Silva and Dobranszki, 2015; Teixeira da Silva and Dobranszki, 2016).

The first report on MF effects on plants dates back to the sixties, with the pioneering work of Krylov and Tarakonova (1960). They proposed an auxin-like effect of the MF on germinating seeds, by calling this effect magnetotropism. The auxin-like effect of MF was also suggested to explain ripening of tomato fruits (Boe and Salunkhe, 1963). Because of the insufficient understanding of the biological action of magnetic fields and its mechanism, it is rare to document the magnetic environment as a controlled factor for scientific experiment. Two experimental approaches aimed to evaluate the physiological responses of plant exposed to MF: response to weak or strong magnetic fields. This chapter updates data of a previously published review (Maffei, 2014).

3.2  Exposure of Plants to Low MF

The term weak or low magnetic field generally refers to the intensities from 100 nT to 0.5 mT, whereas superweak, near-null, or conditionally zero (the so called magnetic vacuum) is related to magnetic fields below 100 nT. Investigations of low MF effects on biological systems have attracted attention of biologists for several reasons. For instance, interplanetary navigation will introduce man, animals, and plants in magnetic environments where the magnetic field is near 1 nT. It is known that a galactic MF induction does not exceed 0.1 nT, in the vicinity of the Sun (0.21 nT), and on the Venus surface (3 nT) (Belov and Bochkarev, 1983). This brought a new wave of interest in MF role in regulating plant growth and development (Belyavskaya, 2004). In the laboratory, low MFs have been created by different methods, including shielding (surrounding the experimental zone by ferromagnetic metal plates with high magnetic permeability, which deviate MF and concentrate it in the metal) and compensating (by using Helmholtz coils) (Bertea et al., 2015). In general, developmental studies on plant responses have been performed at various MF intensities.

3.2.1  Effects of Low MF on Plant Development

Sunflower (Helianthus annuus) seedlings exposed to 20 µT vertical MF showed small, but significant increases in total fresh weights, shoot fresh weights, and root fresh weights, whereas dry weights and germination rates remained unaffected (Fischer et al., 2004).

Pea (Pisum sativum) epicotyls were longer in low magnetic field (11.2 ± 4.2 mm, n = 14) when compared to normal geomagnetic conditions (8.8 ± 4.0 mm, n = 12) (Yamashita et al., 2004). Elongation of pea epicotyl was confirmed, by microscopic observation of sectioned specimen, to result from the elongation of cells and osmotic pressure of seedlings was significantly higher in low MF than controls. This observation suggests that the promotion of cell elongation under low MF may relate to an increase of osmotic pressure in the cells (Negishi et al., 1999). Furthermore, pea seedlings showed ultrastructural peculiarities such as a noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes, and paramural bodies), and reduction of phytoferritin in plastids. Mitochondria were the most sensitive organelles to low MF treatment; and their size and relative volume in cells increased, matrix was electron-transparent, and cristae reduced. It was also observed that low MF effects on ultrastructure of root cells were due to disruptions in different metabolic systems including effects on Ca2+ homeostasis (Belyavskaya, 2001).

In broad bean (Vicia faba) seedlings, low MF intensities of 10 and 100 µT at 50 or 60 Hz were observed to alter membrane transport processes in root tips (Stange et al., 2002), whereas seeds of soybean (Glycine max) exposed to pulsed MF of 1500 nT at 0.1, 1.0 10.0, and 100.0 Hz for 5 h per day for 20 days, induced by enclosure coil systems, significantly increased the rate of seed germination, while 10 and 100 Hz pulsed MFs showed the most effective response (Radhakrishnan and Kumari, 2013). Treatment with MF also improved germination-related parameters like water uptake, speed of germination, seedling length, fresh weight, dry weight, and vigor indices of soybean seeds under laboratory conditions (Shine et al., 2011).

Controversial data have also been reported. The exposure to near null magnetic field of different in vitro cultures of various species of the genus Solanum was either stimulating or inhibiting the growth of in vitro plants. The effect was apparently also dependent on the species, genotype, type of initial explant, treatment duration, or even culture medium (Rakosy-Tican et al., 2005).

By using ferromagnetic shields, the influence of weak, alternating magnetic field, which was adjusted to the cyclotron frequency of Ca2+ and K+ ions, was studied on the fusion of tobacco (Nicotiana tabacum) and soybean protoplasts. It was observed that in these conditions protoplasts fusion increased its frequency 2–3 times with the participation of calcium ions in the induction of protoplast fusion (Nedukha et al., 2007). The observations of the increase in the [Ca2+]cyt level after exposure to very low MF suggest that Ca2+ entry into the cytosol might constitute an early MF sensing mechanism (Belyavskaya, 2001).

When wheat (Triticum aestivum) seeds were treated with low-frequency MF at the stage of esterase activation during seed swelling, the activation of esterases was enhanced by changing qualitatively the time course of the release of reaction products into the medium. These results helped to explain unusual dependences of biological effects on the amplitude of the electromagnetic field (EMF), including the atypical enhancement of these effects by the action of weak low-frequency fields (Aksenov et al., 2000). A two-layer Permalloy magnetic screen was used to test the effects of a wide range of low MF (from 20 nT to 0.1 mT) on 3–5 day old wheat seedlings. It was observed that seedlings grew slower than controls (Bogatina et al., 1978).

Barley (Hordeum vulgare) seedlings grown in Helmholtz coils with a 10 nT MF intensity showed a decrease in fresh weight of shoots (by 12%) and roots (by 35%), as well as dry weight of shoots (by 19%) and roots (by 48%) in comparison with GMF controls. From this pioneer study, it was concluded that very low MF was capable of delaying both organ formation and development (Lebedev et al., 1977).

The effect of a combined magnetic field at the resonance frequency of Ca2+ ions inside a μ-metal shield and the altered gravitropic reaction of cress (Lepidium sativum) roots was performed to evaluate the structure and functional organization of root cap statocytes. The experimented conditions were observed to change normally positively gravitropic cress root to exhibit negative gravitropism (Kordyum et al., 2005).

Artificial shielding of GMF caused a significant decrease in the cell number with enhanced DNA content in root and shoot of onion (Allium cepa) meristems. Furthermore, the uncytokinetic mitosis with formation of binuclear and then tetranuclear cells, as well as a fusion of normal nuclei resulting in appearance of giant cells with vast nuclei, seems to dominate in very low MF conditions (Nanushyan and Murashov, 2001).

Gibberellin (GA) levels and expressions of GA biosynthetic and signaling genes have been studied in wild type Arabidopsis plants and cryptochrome double mutant, cry1/cry2, grown in near-null magnetic field. Wild-type GA4, GA9, GA34, and GA51 levels were significantly decreased in near-null conditions compared with local GMF controls whereas the GA levels in the cry1/cry2 mutants were similar to controls. Expressions of some GA20-oxidase and GA3-oxidase genes in wild type plants were significantly reduced in the near-null MF compared with controls. In contrast, expressions of all the detected GA biosynthetic and signaling genes in cry1/cry2 mutants were not affected by near-null magnetic field. Based on these consideration, Xu and co-workers (Xu et al., 2017a) suggest that the effect of near-null magnetic field on Arabidopsis flowering is GA-related, which is caused by cryptochrome-involved suppression of GA biosynthesis. However, this work did not provide any proteomic or metabolomic evidence in support of the conclusions.

Changes in the ultrastructural organization of some organelles and cellular compartments, alterations in condensed chromatin distribution and reduction in volume of granular nucleolus component with the appearance of nucleolus vacuoles were also found in several other species exposed to very low MF, indicating a decrease in activities of rRNA synthesis in some nucleoli (Belyavskaya, 2004 and references cited therein).

The exposure of Lemna minor plants to reduced GMF significantly stimulated growth rate of the total frond area in the magnetically treated plants and suggest that the efficiency of photosystem II is not affected by variations in GMF (Jan et al., 2015).

3.2.2  Effects of Low MF on Transition to Flowering

Near-null magnetic field can be produced by three mutually perpendicular couples of Helmholtz coils and three sources of high-precision direct current power, which can counteract the vertical, north–south and east–west direction components of the geomagnetic field (Xu et al., 2012; Bertea et al., 2015).

Perilla plants (Perilla nankinensis Lour. Decne.) grown in weak permanent horizontal magnetic field (PHMF) of 500 µT flux density under controlled illumination, temperature, and humidity retarded plant flowering as compared to control. This treatment increased total lipid content, including polar lipids, among them glycolipids and phospholipids; however, it did not affect the content of neutral lipids. These studies indicate that PHMF stimulated synthesis of membrane lipids of chloroplasts, mitochondria, and cytoplasm in Perilla leaves (Novitskii et al., 2016).

Although the functions of cryptochrome have been well demonstrated for Arabidopsis thaliana, the effect of the GMF on the growth of Arabidopsis and its mechanism of action are poorly understood. In Arabidopsis, seedlings grown in a near-null magnetic field show a flowering delay of ca. 5 days compared with those grown in the GMF. Moreover, PCR analyses of three cryptochrome-signaling-related genes, PHYB, CO, and FT also changed; the transcript level of PHYB was elevated ca. 40%, and that of CO and FT was reduced ca. 40% and 50%, respectively. These data suggest that the effects of a near-null magnetic field on Arabidopsis might be cryptochrome-related, which may be revealed by a modification of the active state of cryptochrome and the subsequent signaling cascade (Xu et al., 2012). Moreover, the biomass accumulation of plants in the near-null magnetic field was significantly suppressed at the time when plants were switching from vegetative growth to reproductive growth compared with that of plants grown in the local GMF, which was caused by the delay in the flowering of plants in the near-null magnetic field conditions. These resulted in a significant reduction of about 20% in the harvest index of plants in the near-null magnetic field compared with that of the controls. Therefore, the removal of the local geomagnetic field negatively affects the reproductive growth of Arabidopsis, which thus affects the yield and harvest index (Xu et al., 2013).

To further demonstrate that the effect of near-null magnetic field on Arabidopsis flowering is associated with CRY, Arabidopsis wild type and cry mutant plants were grown in the near-null magnetic field under blue or red light with different light cycle and photosynthetic photon flux density. Arabidopsis flowering was significantly suppressed by near-null magnetic field in blue light with lower intensity and shorter cycle (12 h period: 6 h light/6 h dark). However, flowering time of cry1/cry2 mutants did not show any difference between plants grown in near-null magnetic field and in local geomagnetic field under detected light conditions. In red light, no significant difference was shown in Arabidopsis flowering between plants in near-null magnetic field and local geomagnetic field under detected light cycles and intensities. According to Xu and co-workers (Xu et al., 2015), these results suggest that changes of blue light cycle and intensity alter the effect of near-null magnetic field on Arabidopsis flowering, which is mediated by CRY. However, much more is still to be understood and a thorough proteomic and transcriptomic analysis is needed to better understand the involvement of photoreceptors in GMF perception.

3.3  Exposure of Plants to MF Intensities Higher than the Geomagnetic Filed

A consistent number of papers described the effect of MF intensities higher than the GMF levels. In general, intensities higher than the GMF relate to values higher than 100 µT. Experimental values can reach very high MF levels, ranging from 500 µT up to 15 T. Most of the attention has been focused on seed germination of important crops like wheat, rice, and legumes. However, many other physiological effects of high MF on plants described plant responses in terms of growth, development, photosynthesis, and redox status.

3.3.1  Effects of High MF on Germination

Standardization of magnetic field was done for maximum enhancement in germination characteristics of maize seeds. Seeds of maize were exposed to static magnetic fields of strength 50, 100, 150, 200, and 250 mT for 1, 2, 3, and 4 h for all field strengths. MF application enhanced percentage germination, speed of germination, seedling length, and seedling dry weight compared to unexposed control. 200 mT for 1 h exposure was found to provide the best results. Furthermore, MF exposure improved seed coat membrane integrity by reducing cellular leakage and, consequently, electrical conductivity. Experiments conducted at a research farm showed that exposure to 200 mT for 1 h prompted higher values of leaf area index, shoot length, number of leaves, chlorophyll content, shoot/root dry weight, and increased seed yield as compared to corresponding values in untreated control (Vashisth and Joshi, 2017).

Aged green pea seeds were magnetoprimed by exposure to pulsed MF of 100 mT for 1 h in three pulsed modes. The 6 min on and off MF showed significant improvement in germination (7.6%) and vigor (84.8%) over aged seeds (Bhardwaj et al., 2016).

In soybean, exposure to 100 and 200 mT MF effectively slowed the rate of biochemical degradation and loss of cellular integrity in seeds stored under conditions of accelerated aging and thus, protected the deterioration of seed quality (Kumar et al., 2015).

The speed of germination was in general increased for Pinus taeda L. seeds treated with a static MF of 150 mT for 10, 30, and 60 min, whereas a negative impact was found in seeds treated for 24 and 48 h (Yao and Shen, 2015).

A magnetic field applied to dormant seeds was found to increase the rate of subsequent seedling growth of barley, corn (Zea mays), beans, wheat, certain tree fruits, and other tree species. Moreover, a low-frequency magnetic field (16 Hz) can be used as a method of post-harvest seed improvement for different plant species, especially for seeds of temperature sensitive species germinating at low temperatures (Rochalska and Orzeszko-Rywka, 2005).

Seeds of hornwort (Cryptotaenia japonica) exposed to sinusoidally time-varying extremely low-frequency (ELF) magnetic fields (AC fields) in combination with the local GMF showed a promoted activity of cells and enzymes in germination stage of the seed. This suggests that an optimum ELF MF might exist for the germination of hornwort seeds under the local GMF (Kobayashi et al., 2004). The application of AC field also promoted the germination of bean (Phaseolus vulgaris) seeds (Sakhnini, 2007).

In seeds of mung bean (Vigna radiata), exposed in batches to static magnetic fields of 87–226 mT intensity for 100 min, a linear increase in germination magnetic constant with increasing intensity of MF was found. Calculated values of mean germination time, mean germination rate, germination rate coefficient, germination magnetic constant, transition time, and water uptake indicate that the impact of applied static MF improves the germination of mung beans seeds even in off-season (Mahajan and Pandey, 2014).

The seeds of pea exposed to full-wave rectified sinusoidal nonuniform MF of strength 60, 120, and 180 mT for 5, 10, and 15 min prior to sowing showed significant increase in germination. The emergence index, final emergence index, and vigor index increased by 86%, 13%, and 205%, respectively. Furthermore, it was found that exposure of 5 min for MF strengths of 60 and 180 mT significantly enhanced the germination parameters of the pea and these treatments could be used practically to accelerate the germination in pea (Iqbal et al., 2012).

MF application with a strength from 0 to 250 mT in steps of 50 mT for 1–4 h significantly enhanced speed of germination, seedling length, and seedling dry weight compared to unexposed control in chickpea (Cicer arietinum). It was also found that magnetically treated chickpea seeds may perform better under rainfed (un-irrigated) conditions where there was a restrictive soil moisture regime (Vashisth and Nagarajan, 2008).

Different intensities of static MF (4 or 7 mT) were tested on seed germination and seedling growth of bean or wheat seeds in different media having 0, 2, 6, and 10 atmospheres osmotic pressure prepared with sucrose or salt. The application of both MFs promoted the germination ratios, regardless of increasing osmotic pressure of sucrose or salt. The greatest germination and growth rates in both plants were from the test groups exposed to 7 mT (Cakmak et al., 2010).

Wheat seeds were imbibed in water overnight and then treated with or without a 30 mT static magnetic field (SMF) and a 10 kHz electromagnetic field (EMF) for 4 days, each 5 h. Exposure to both MF increased the speed of germination, compared to the control group, suggesting promotional effects of EMFs on membrane integrity and growth characteristics of wheat seedlings (Payez et al., 2013).

Pre-sowing treatment of corn seeds with pulsed electromagnetic fields for 0, 15, 30, and 45 min improved germination percentage, vigor, chlorophyll content, leaf area, plant fresh and dry weight, and finally yields. Seeds that have been exposed to magnetic field for 30 and 45 min have been found to perform the best results with economic impact on producer’s income in a context of a modern, organic, and sustainable agriculture (Bilalis et al., 2012).

Various combinations of MF strength and exposure time significantly improved tomato (Solanum lycopersicum) cv. Lignon seed performance in terms of reduction of time required for the first seeds to complete germination, time to reach 50% germination, time between 10 and 90% germination with increasing germination rate, and increased germination percentage at 4 and 7 days, seedling shoot and root length compared to the untreated control seeds. The combinations of 160 mT for 1 min and 200 mT for 1 min gave the best results (De Souza et al., 2010). Higher germination (about 11%) was observed in magnetically exposed tomato var. MST/32 seed than in non-exposed ones, suggesting a significant effect of nonuniform MFs on seed performance with respect to relative humidity (RH) (Poinapen et al., 2013a).

The effect of pre-sowing magnetic treatments was investigated on germination, growth, and yield of okra (Abelmoschus esculentus cv. Sapz paid) with an average magnetic field exposure of 99 mT for 3 and 11 min. A significant increase (P < 0.05) was observed in germination percentage, number of flowers per plant, leaf area, plant height at maturity, number of fruits per plant, pod mass per plant, and number of seeds per plant. The 99 mT for 11 min exposure showed better results as compared to control (Naz et al., 2012).

However, contrasting results have also been reported. For instance, the mean germination time of rice (Oryza sativa) seeds exposed to one of two magnetic field strengths (125 or 250 mT) for different times (1 min, 10 min, 20 min, 1 h, 24 h, or chronic exposure) was significantly reduced compared to controls, indicating that this type of magnetic treatment clearly affects germination and the first stages of growth of rice plants (Florez et al., 2004).

3.3.2  Effects of High MF on Cryptochrome

The blue light receptor cryptochrome can form radical pairs after exposure to blue light and has been suggested to be a potential magnetoreceptor based on the proposition that radical pairs are involved in magnetoreception. Nevertheless, the effects of MF on the function of cryptochrome are poorly understood. When Arabidopsis seedlings were grown in a 500 μT magnetic field and a near-null MF it was found that the 500 μT MF enhanced the blue light-dependent phosphorylations of CRY1 and CRY2, whereas the near-null magnetic field weakened the blue light-dependent phosphorylation of CRY2 but not CRY1. Dephosphorylations of CRY1 and CRY2 in the darkness were slowed down in the 500 μT MF, whereas dephosphorylations of CRY1 and CRY2 were accelerated in the near-null MF. These results suggest that MF with strength higher or weaker than the local geomagnetic field affects the activated states of cryptochromes, which thus modifies the functions of cryptochromes (Xu et al., 2014). Moreover, the magnitude of the hyperfine coupling constants (Amax (iso) = 1.75 mT) suggests that artificial magnetic fields (0.1–0.5 mT) involved in experiments with Arabidopsis can affect the signal transduction rate. On the other hand, hyperfine interactions in the FADH-Trp•+ biradicals are much stronger than the Zeeman interaction with the magnetic field of the Earth (≈0.05 mT). Therefore, an alternative mechanism for the bird avian compass has been proposed recently. This mechanism involves radicals with weaker hyperfine interactions (O2 •− and FADH), and thus, it could be more plausible for explaining incredible sensitivity of some living species to even tiny changes in the MF (Izmaylov et al., 2009).

Contrasting results were obtained when the intensity of the ambient magnetic field was varied from 33–44 to 500 μT. According to Ahmad et al. (2007), there was an enhanced growth inhibition in Arabidopsis under blue light, when cryptochromes are the mediating photoreceptor, but not under red light when the mediating receptors are phytochromes, or in total darkness. Hypocotyl growth of Arabidopsis mutants lacking cryptochromes was unaffected by the increase in magnetic intensity. Additional cryptochrome-dependent responses, such as blue-light-dependent anthocyanin accumulation and blue-light-dependent degradation of CRY2 protein, were also enhanced at the higher magnetic intensity. On the contrary, Harris et al. (2009), by using the experimental conditions chosen to match those of the Ahmad study, found that in no case consistent, statistically significant magnetic field responses were detected. For a more comprehensive discussion on cryptochromes, see below.

3.3.3  Effects of High MF on Roots and Shoots

Increased growth rates have been observed in different species when seeds where treated with increased MF. Treated corn plants grew higher and heavier than control, corresponding with increase of the total fresh weight. The greatest increases were obtained for plants continuously exposed to 125 or 250 mT (Florez et al., 2007). A stimulating effect on the first stages of growth of barley seeds was found for all exposure times studied. When germinating barley seeds were subjected to a magnetic field of 125 mT for different times (1, 10, 20, and 60 min, 24 h, and chronic exposure), increases in length and weight were observed (Martinez et al., 2000). Pants of pea exposed to 125 or 250 mT stationary MF generated by magnets under laboratory conditions for 1, 10 and 20 min, 1 and 24 h and continuous exposure were longer and heavier than the corresponding controls at each time of evaluation. The major increases occurred when seeds were continuously exposed to the MF (Carbonell et al., 2011).

Z. mays plants exposed to modulated continuous wave homogenous MF at specific absorption rate (SAR) of 1.69 ± 0.0 × 10−1 W kg−1 for A1/2, 1, 2, and 4 h for 7 days revealed that short-term exposure did not induce any significant change, while longer exposure of 4 h caused significant growth and biochemical alterations. Maize plants showed a reduction in the root and coleoptile length with more pronounced effect on coleoptile growth (23% reduction on 4 h exposure) (Kumar et al., 2016).

By treating with twice-gradient MF Dioscorea opposita, it was found that they could grow best in the seedling stage. Compared with the control, the rate of emergence increased by 39%, root number increased by 8%, and the average root length increased by 2.62 cm (Li, 2000). The 16 Hz frequency and 5 mT MF as well as alternating MF influence increased sugar beet (Beta vulgaris var. saccharifera) root and leaf yield (Rochalska, 2008), while a dramatic increase in root length, root surface area, and root volume was observed in chickpea exposed in batches to static MF of strength from 0 to 250 mT in steps of 50 mT for 1–4 h (Vashisth and Nagarajan, 2008). In the same conditions, seedlings of sunflower showed higher seedling dry weight, root length, root surface area, and root volume. Moreover, in germinating seeds, enzyme activities of α-amylase, dehydrogenase, and protease were significantly higher in treated seeds than controls (Vashisth and Nagarajan, 2010).

3.3.4  Effects of High MF on Gravitropic Responses

The growth response that is required to maintain the spatial orientation is called gravitropism and consists of three phases: reception of a gravitational signal, its transduction to a biochemical signal that is transported to the responsive cells and finally the growth response, or bending of root or shoot. Primary roots exhibit positive gravitropism, i.e., they grow in the direction of a gravitational vector. Shoots respond negatively gravitropic and grow upright opposite to the gravitational vector. However, lateral roots and shoots branches are characterized by intermediate set-point angles and grow at a particular angle that can change over time (Firn and Digby, 1997). Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient MF provides a new approach to selectively manipulate the gravisensing system.

High-gradient MF has been used to induce intracellular magnetophoresis of amyloplasts and the obtained data indicate that a magnetic force can be used to study the gravisensing and response system of roots (Kuznetsov and Hasenstein, 1996). The data reported strongly support the amyloplast-based gravity-sensing system in higher plants and the usefulness of high MF to substitute gravity in shoots (Kuznetsov and Hasenstein, 1997; Kuznetsov et al., 1999). For example, in shoots of the lazy-2 mutant of tomato that exhibit negative gravitropism in the dark, but respond positively gravitropically in (red) light, induced magnetophoretic curvature showed that lazy-2 mutants perceive the displacement of amyloplasts in a similar manner than wild type and that the high MF does not affect the graviresponse mechanism (Hasenstein and Kuznetsov, 1999). Arabidopsis stems positioned in a high MF on a rotating clinostat demonstrate that the lack of apical curvature after basal amyloplast displacement indicates that gravity perception in the base is not transmitted to the apex (Weise et al., 2000). The movement of corn, wheat, and potato (Solanum tuberosum) starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20–25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external MF that caused repulsion of starch grains. Magnetic gradients were able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments (Hasenstein et al., 2013). The response of transgenic seedlings of Arabidopsis, containing either the CycB1-GUS proliferation marker or the DR5-GUS auxin-mediated growth marker, to diamagnetic levitation in the bore of a superconducting solenoid magnet was evaluated. Diamagnetic levitation led to changes that are very similar to those caused by real [i.e., on board the International Space Station (ISS)] or mechanically simulated microgravity [i.e., using a random positioning machine (RPM)]. These changes decoupled meristematic cell proliferation from ribosome biogenesis, and altered auxin polar transport (Manzano et al., 2013). Arabidopsis in vitro callus cultures were also exposed to environments with different levels of effective gravity and MF strengths simultaneously. The MF itself produced a low number of proteomic alterations, but the combination of gravitational alteration and MF exposure produced synergistic effects on the proteome of plants (Herranz et al., 2013). However, MF leads to redistribution of the cellular activities and this is why application of the proteomic analysis to the whole organs/plants is not so informative.

3.3.5  Effects of High MF on Redox Status

Effects of MFs have been related to uncoupling of free radical processes in membranes and enhanced ROS generation. It has been experimentally proven that MF can change activities of some scavenging enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), glutathione transferase (GT), peroxidase (POD), ascobtate peroxidase (APX), and polyphenoloxidase (POP). Experiments have been performed on several plant species, including pea, land snail (Helix aspesa), radish (Raphanus sativus), Leymus chinensis, soybean, cucumber (Cucumis stivus), broad bean, corn, parsley (Petroselinum crispum), and wheat (Xia and Guo, 2000; Regoli et al., 2005; Baby et al., 2011; Polovinkina et al., 2011; Anand et al., 2012; Bhardwaj et al., 2012; Jouni et al., 2012; Radhakrishnan and Kumari, 2012; Shine and Guruprasad, 2012; Shine et al., 2012; Payez et al., 2013; Radhakrishnan and Kumari, 2013; Rajabbeigi et al., 2013; Serdyukov and Novitskii, 2013; Aleman et al., 2014; Haghighat et al., 2014). The results suggest that exposure to increased MF causes accumulation of reactive oxygen species and alteration of enzyme activities.

The effects of continuous, low-intensity static MF (7 mT) and EF (20 kV/m) on antioxidant status of shallot (Allium ascalonicum) leaves, increased lipid peroxidation and H2O2 levels in EF applied leaves. These results suggested that apoplastic constituents may work as potentially important redox regulators sensing and signaling MF changes. Static continuous MF and EF at low intensities have distinct impacts on the antioxidant system in plant leaves, and weak MF is involved in antioxidant-mediated reactions in the apoplast, resulting in overcoming a possible redox imbalance (Cakmak et al., 2012).

In mung bean seedlings treated with 600 mT MF followed by cadmium stress the concentration of malondialdehyde, H2O2 and O2 , and the conductivity of electrolyte leakage decreased, while the NO concentration and NOS activity increased compared to cadmium stress alone, showing that magnetic field compensates for the toxicological effects of cadmium exposure are related to NO signal (Chen et al., 2011).

Superoxide and hydrogen peroxide production increased in green pea germinating primed seeds by 27% and 52%, respectively, over aged seeds when exposed to 100 mT MF. In particular, NADH peroxidase and superoxide dismutase involved in generation of H2O2 showed increased activity in MF primed seeds. Increase in catalase, ascorbate peroxidase and glutathione reductase activity after 36 h of imbibition in primed seeds demonstrated its involvement in seed recovery during magnetopriming. An increase in total antioxidants also helped in maintaining the level of free radicals for promoting germination of magnetoprimed seeds. A 44% increase in the level of protein carbonyls after 36 h indicated involvement of protein oxidation for counteracting and/or utilizing the production of ROS and faster mobilization of reserve proteins. Higher production of free radicals in primed seeds did not cause lipid peroxidation as malondialdehyde content was low. Lipoxygenase was involved in the germination-associated events as the magnitude of activity was higher in primed aged seeds compared to aged seeds. This study elucidated that MF-mediated improvement in seed quality of aged pea seeds was facilitated by fine tuning of free radicals by the antioxidant defense system and protein oxidation (Bhardwaj et al., 2016).

3.3.6  Effects of High MF on Photosynthesis

Photosynthesis, stomatal conductance, and chlorophyll content increased in corn plants exposed to static MFs of 100 and 200 mT, compared to control under irrigated and mild stress condition (Anand et al., 2012).

Pre-seed electromagnetic treatments have been used to minimize the drought-induced adverse effects on different crop plants. Pretreatment of seeds of two corn cultivars with different magnetic treatments significantly alleviated the drought-induced adverse effects on growth by improving chlorophyll a (Chl a) and photochemical quenching and non-photochemical quenching. Of all magnetic treatments, 100 and 150 mT for 10 min were most effective in alleviating the drought-induced adverse effects (Javed et al., 2011).

Polyphasic Chl a fluorescence transients from magnetically treated soybean plants gave a higher fluorescence yield. The total soluble proteins of leaves showed increased intensities of the bands corresponding to a larger subunit (53 KDa) and smaller subunit (14 KDa) of Rubisco in the treated plants. Therefore, pre-sowing magnetic treatment was found to improve biomass accumulation in soybean (Shine et al., 2011).

Other general effects on MF application on chlorophyll content have been documented for several plant species (Voznyak et al., 1980; Rochalska, 2005; Turker et al., 2007; Radhakrishnan and Kumari, 2013).

The CO2 uptake rate of MF exposed radish seedlings was lower than that of the control seedlings. The dry weight and the cotyledon area of MF exposed seedlings were also significantly lower than those of the control seedlings (Yano et al., 2004).

A MF of around 4 mT had beneficial effects, regardless of the direction of magnetic field, on the growth promotion and enhancement of CO2 uptake of potato plantlets in vitro. However, the direction of magnetic field at the MF tested had no effects on the growth and CO2 exchange rate (Iimoto et al., 1998).

A permanent magnetic field induces significant changes in bean leaf fluorescence spectra and temperature. The fluorescence intensity ratio (FIR) and change of leaf temperature ΔT increase with the increase of magnetic field intensity. The increase of ΔT due to magnetic fields is explained in bean with a simple ion velocity model. Reasonable agreement between calculated ΔT, based on the model, and measured ΔT was obtained (Jovanic and Sarvan, 2004).

The contents of maize photosynthetic pigments and total carbohydrates declined by 13% and 18%, respectively, in 4 h exposure treatments to increased MF compared to unexposed control (Kumar et al., 2016). Furthermore, the activity of starch-hydrolyzing enzymes α- and β-amylases increased by similar to 92% and 94%, respectively, at an exposure duration of 4 h, over that in the control. In response to 4 h exposure treatment, the activity of sucrolytic enzymes acid invertases and alkaline invertases increased by 88% and 266%, whereas the specific activities of phosphohydrolytic enzymes (acid phosphatases and alkaline phosphatases) showed initial increase and then declined at >2 h exposure duration. The results of this study indicate MF inhibited seedling growth of Z. mays by interfering with starch and sucrose metabolism (Kumar et al., 2016).

The effects of enhanced MF on growth and Chl a fluorescence of Lemna minor plants were investigated under controlled conditions in extreme geomagnetic environments of 150 mT. The strong static magnetic field seems to have the potential to increase initial Chl a fluorescence and energy dissipation in Lemna minor plants (Jan et al., 2015).

3.3.7  Effects of High MF on Lipid Composition

In radish seedlings grown in lowlight and darkness in an extremely low frequency (ELF) magnetic field characterized by 50 Hz frequency and approximate to 500 µT flux density, MF exposure increased the production of polar lipids by threefold specifically, glycolipids content increased fourfold, and phospholipids content rose 2.5 times, compared to seeds. MF stimulated lipid synthesis in chloroplast, mitochondrial, and other cell membranes (Novitskii et al., 2014). Furthermore, among fatty acids, MF exerted the strongest effect on the content of erucic acid: it increased in the light and in darkness approximately by 25% and decreased in the light by 13%. Therefore, MF behaved as a correction factor affecting lipid metabolism on the background of light and temperature action (Novitskaya et al., 2010).

Plasma membranes of seeds of tomato plants were purified, extracted, and applied to a silicon substrate in a buffer suspension and their molecular structure was studied using X-ray diffraction. While MFs had no observable effect on protein structure, enhanced lipid order was observed, leading to an increase in the gel components and a decrease in the fluid component of the lipids (Poinapen et al., 2013b).

A field experiment on cardoon seeds (Cynara cardunculus L.) was carried out during two successive seasons to study the effect of electromagnetic fields (EMF) on cardoon growth and its palmitic acid content. A 75 mT (millitesla) MF was used on cardoon seeds (Cynara cardunculus L.) during two successive seasons to study the effect of MF on plant growth and palmitic acid content. The EMF had significant effects on the palmitic acid (C16:0) content in producing seeds and the maximum value of palmitic acid content was 11.83% compared to a control value of 9.30%. These results suggest that MF treatments of cardoon seeds might have the potential to enhance the cardoon plant growth and the palmitic acid content (Sharaf-Eldin, 2016).

3.3.8  Other Effects of High MF on Plants

MF-induced DNA damage and methylation was studied in wheat calli by using random amplified polymorphic DNA and coupled restriction enzyme digestion-random amplification techniques. When calli were exposed to 7 mT static MF for 24, 48, 72, 96, or 120 h of incubation, the highest change in polymorphism rate was obtained after 120 h in both 7- and 14-day-old calli. Moreover, increase in MF duration caused DNA hypermethylation in both 7- and 14-day-old calli. The highest methylation level with a value of 25.1% was found in 7-day-old calli exposed to MF for 120 h (Aydin et al., 2016).

The effectiveness of magnetopriming was assessed for alleviation of salt-induced adverse effects on soybean growth. Soybean seeds were pretreated with static MF of 200 mT for 1h to evaluate the effect of magnetopriming on growth, carbon and nitrogen metabolism, and yield of soybean plants under different salinity levels (0, 25, and 50 mM NaCl). MF pretreatment significantly increased the number of root nodules, nodules, fresh weight, biomass accumulation, and photosynthetic performance under both nonsaline and saline conditions as compared to untreated seeds. Furthermore, nitrate reductase activity, PIABS, photosynthetic pigments, and net rate of photosynthesis were also higher in plants that emerged from MF pretreated seeds as compared to untreated seeds. MF pretreatment also increased leghemoglobin content and hemechrome content in root nodules, indicating that pre-sowing exposure of seeds to MF enhanced carbon and nitrogen metabolism, improved the yield of soybeans and alleviated salinity stress (Baghel et al., 2016).

Inflorescences from Tradescantia clones subjected to high MF showed pink mutations in stamen hair cells were observed (Baum and Nauman, 1984), whereas pollen grains of papaya (Carica papaya) exposed to MF germinated faster and produced longer pollen tubes than the controls (Alexander and Ganeshan, 1990).

In kiwifruit (Actinidia deliciosa), MF treatment partially removed the inhibitory effect caused by the lack of Ca2+ in the pollen culture medium, inducing a release of internal Ca2+ stored in the secretory vesicles of pollen plasma membrane (Betti et al., 2011).

Short day strawberry (Fragaria vesca) plants treated with MF strengths of 0.096, 0.192, and 0.384 Tesla (T) in heated greenhouse conditions showed increased fruit yield per plant (208.50 and 246.07 g, respectively) and fruit number per plant (25.9 and 27.6, respectively), but higher MF strengths than 0.096 T reduced fruit yield and fruit number. Increasing MF strength from control to 0.384 T also increased contents of N, K, Ca, Mg, Cu, Fe, Mn, Na, and Zn, but reduced P and S contents (Esitken and Turan, 2004).

The effects of pre-sowing magnetic treatments on growth and yield of tomato increased significantly (P < 0.05) the mean fruit weight, the fruit yield per plant, the fruit yield per area, and the equatorial diameter of fruits in comparison with the controls. Total dry matter was also significantly higher for plants from magnetically treated seeds than controls (De Souza et al., 2006).

In the presence of a static MF, the rhythmic leaflet movements of the plant Desmodium gyrans tended to slowdown. Leaflets moving up and down in a MF of approximately 50 mT flux density increased the period by about 10% due to a slower motion in the “up” position. Since, during this position, a rapid change of the extracellular potentials of the pulvinus occurs, it was proposed that the effects could be mediated via the electric processes in the pulvinus tissue (Sharma et al., 2000).

Electric process implies ion flux variations. The influence of a high-gradient MF on spatial distribution of ion fluxes along the roots, cytoplasmic streaming, and the processes of plant cell growth connected with intracellular mass and charge transfer was demonstrated (Kondrachuk and Belyavskaya, 2001).

In tomato, a significant delay in the appearance of first symptoms of geminivirus and early blight and a reduced infection rate of early blight were observed in the plants from exposed seeds to increased MFs (De Souza et al., 2006).

Single suspension-cultured plant cells of the Madagascar rosy periwinkle (Catharanthus roseus) and their protoplasts were anchored to a glass plate and exposed to a MF of 302 ± 8 mT for several hours. Analysis suggested that exposure to the magnetic field roughly tripled Young’s modulus of the newly synthesized cell wall without any lag (Haneda et al., 2006).

In vitro tissue cultures of Paulownia tomentosa and Paulownia fortunei exposed to a magnetic flow density of 2.9–4.8 mT and 1 m s−1 flow rate for a period of 0, 2.2, 6.6, and 19.8 s showed increased regeneration capability of Paulownia cultures and a shortening of the regeneration time. When the cultures were exposed to a MF with strength of 2.9–4.8 mT for 19.8 s, the regenerated P. tomentosa and P. fortunei plants dominated the control plants (Yaycili and Alikamanoglu, 2005).

Increase in MF conditions may also affect secondary plant metabolism. The growth of suspension cultures of Taxus chinensis var. mairei and Taxol production were promoted both by a sinusoidal alternating current magnetic field (50 Hz, 3.5 mT) and by a direct current magnetic field (3.5 mT). Taxol production increased rapidly from the fourth day with the direct current MF but most slowly with the alternating current MF. The maximal yield of Taxol was 490 µg l−1 with the direct current MF and 425 µg l−1 with the alternating current MF after 8 days of culture, which were, respectively, 1.4-fold and 1.2-fold of that without exposure to a MF (Shang et al., 2004).

The biological impact of MF strengths up to 30 T on transgenic Arabidopsis plants engineered with a stress response gene consisting of the alcohol dehydrogenase (Adh) gene promoter driving the β-glucuronidase (GUS) gene reporter. Field strengths in excess of about 15 T induce expression of the Adh/GUS transgene in the roots and leaves. From the microarray analyses that surveyed 8,000 genes, 114 genes were differentially expressed to a degree greater than 2.5-fold over the control. The data suggest that MF in excess of 15 T have far-reaching effect on the genome. The widespread induction of stress-related genes and transcription factors, and a depression of genes associated with cell wall metabolism, are prominent examples. The roles of magnetic field orientation of macromolecules and magnetophoretic effects are possible factors that contribute to the mounting of this response (Paul et al., 2006).

The influence of high MF was also studied on the growth and biomass composition of Spirulina sp. and Chlorella fusca cultivated in vertical tubular photobioreactors. MFs of 30 and 60 mT for 1 h d−1 stimulated Spirulina growth, leading to higher biomass concentration by comparison with the control culture. Increase in productivity, protein and carbohydrate contents were also observed by showing that MF may also influence the growth of Spirulina sp. (Deamici et al., 2016a,b).

3.4  Possible Mechanisms of Magnetoreception

For a number of years, laboratory studies on the biological effects of MF have demonstrated that MFs can produce or alter a wide range of phenomena. Explaining the diversity of the reported effects is a central problem. In recent years, the following types of physical processes or models underlying hypothetically primary mechanisms of the interaction of MF responses in biological systems have been proposed: (a) classical and quantum oscillator models; (b) cyclotron resonance model; (c) interference of quantum states of bound ions and electrons; (d) coherent quantum excitations; (e) biological effects of torsion fields accompanying MF; (f) biologically active metastable states of liquid water; (g) free-radical reactions and other “spin” mechanisms; (h) parametric resonance model; (i) stochastic resonance as an amplifier mechanism in magnetobiology and other random processes; (j) phase transitions in biophysical systems displaying liquid crystal ordering; (k) bifurcation behavior of solutions of nonlinear chemical kinetics equations; (l) radio-technical models, in which biological structures and tissues are portrayed as equivalent electric circuits; and (m) macroscopic charged vortices in cytoplasm. Although mechanisms combining these concepts and models cannot be excluded (Belyavskaya, 2004), a critical survey is needed (see also Chapter 7 in BBA).

Observation of resonance effects at specific frequencies, combined with new theoretical considerations and calculations, indicates that birds use a radical pair with special properties that is optimally designed as a receptor in a biological compass. This radical pair design might be realized by cryptochrome photoreceptors if paired with molecular oxygen as a reaction partner (Ritz et al., 2009; Ritz et al., 2010). Therefore, several considerations have suggested that cryptochromes are likely to be the primary sensory molecules of the light-dependent magnetodetection mechanism, which has been suggested to be radical pair based (Liedvogel and Mouritsen, 2010). The molecular mechanism that leads to formation of a stabilized, magnetic field–sensitive radical pair has despite various theoretical and experimental efforts not been unambiguously identified yet. By using a quantum mechanical molecular dynamics approach, it was possible to follow the time evolution of the electron transfer in an unbiased fashion and to reveal the molecular driving force that ensures fast electron transfer in cryptochrome guaranteeing formation of a persistent radical pair suitable for magnetoreception (Ludemann et al., 2015).

In plants, cryptochromes control different aspects of growth and development (Wang et al., 2014; Liu et al., 2016); i.e., involvement in de-etiolation responses such as inhibition of hypocotyl growth (Ahmad and Cashmore, 1993; Lin, 2002), anthocyanin accumulation (Ahmad et al., 1995), leaf and cotyledon expansion (Cashmore et al., 1999; Lin, 2002), transitions to flowering (El-Assal et al., 2003), or regulation of blue-light-regulated genes (Jiao et al., 2003). In Arabidopsis, cryptochromes are encoded by two similar genes, cry1 and cry2. CRY2 protein levels in seedlings decrease rapidly upon illumination by blue light, presumably as a result of protein degradation of the light-activated form of the receptor (Ahmad et al., 2007). Like photolyases, plant cryptochromes undergo a light-dependent electron transfer reaction, known as photoactivation, that leads to photoreduction of the flavin cofactor, FAD (Giovani et al., 2003).

Particular attention has been paid to the potential role of cryptochrome as a plant magnetosensor (Ahmad and Cashmore, 1993; Ang et al., 1998; Chattopadhyay et al., 1998; Mockler et al., 1999; Lin, 2002; El-Assal et al., 2003; Giovani et al., 2003; Jiao et al., 2003; Zeugner et al., 2005; Ahmad et al., 2007; Bouly et al., 2007; Kleine et al., 2007; Solov’yov et al., 2008; Harris et al., 2009; Liedvogel and Mouritsen, 2010; Ritz et al., 2010; Solov’yov and Schulten, 2012; Wan et al., 2015; Wan et al., 2016; Wang et al., 2016; Xu et al., 2017a, b).

Experiments on Arabidopsis have suggested that magnetic intensity affects cryptochrome-​dependent growth responses (Ahmad et al., 2007). But, as discussed above, these reported cryptochrome-mediated magnetic field effects on plant growth could not be replicated in an independent study (Harris et al., 2009). These findings would be very important, if they turn out to exist and be independently replicable, since even though magnetic responses do not seem biologically relevant for the plant, they would show in principle that biological tissue is sensitive to the magnetic field responses that are linked to cryptochrome-dependent signaling pathways. They could thus confirm the ability of cryptochrome to mediate magnetic field responses (Liedvogel and Mouritsen, 2010).

The claimed magnetosensitive responses can best be explained by the radical pair model, as Arabidopsis cryptochromes form radical pairs after photoexcitation (Giovani et al., 2003; Zeugner et al., 2005; Bouly et al., 2007) and these experiments might reflect common physical properties of photoexcited cryptochromes in both plants and animals.

The radical-pair mechanism is currently the only physically plausible mechanism by which magnetic interactions that are orders of magnitude weaker than the average thermal energy, k BT, can affect chemical reactions. The kinetics and quantum yields of photo-induced flavin-tryptophan radical pairs in cryptochrome are indeed magnetically sensitive and cryptochrome is a good candidate as a chemical magnetoreceptor. Cryptochromes have also attracted attention as potential mediators of biological effects of extremely low frequency (ELF) electromagnetic fields and possess properties required to respond to Earth-strength (approximately 50 μT) fields at physiological temperatures (Maeda et al., 2012).

Recently, a combination of quantum biology and molecular dynamics simulations on plant cryptochrome has demonstrated that after photoexcitation a radical pair forms, becomes stabilized through proton transfer, and decays back to the protein’s resting state on time scales allowing the protein, in principle, to act as a radical pair-based magnetic sensor (Solov’yov and Schulten, 2012 and references therein; Maffei, 2014; Occhipinti et al., 2014). Furthermore, the elimination of the local geomagnetic field weakens the inhibition of Arabidopsis hypocotyl growth by white light, and delays flowering time. The expression changes of three Arabidopsis cryptochrome-signaling-related genes (PHYB, CO, and FT) suggest that the effects of a near-null magnetic field are cryptochrome-related, which may be revealed by a modification of the active state of cryptochrome and the subsequent signaling cascade plant cryptochrome has been suggested to act as a magnetoreceptor (Xu et al., 2012).

3.5  Conclusion and Perspectives

Revealing the relationships between MF and plant responses is becoming more and more important as new evidence reveals the ability of plants to perceive and respond quickly to varying MF by altering their gene expression and phenotype. The recent implications of MF reversal with plant evolution (Occhipinti et al., 2014; Bertea et al., 2015) open new horizons not only in plant science but also to the whole biosphere, from the simplest organisms to human beings.

Magnetotactic bacteria are a diverse group of microorganisms with the ability to orient and migrate along geomagnetic field lines (Yan et al., 2012); the avian magnetic compass has been well characterized in behavioral tests (Ritz et al., 2009); magnetic alignment, which constitutes the simplest directional response to the GMF, has been demonstrated in diverse animals including insects, amphibians, fish, and mammals (Begall et al., 2013); concerns of possible biological effects of environmental electromagnetic fields on the basis of the energy required to rotate the small crystals of biogenic magnetite that have been discovered in various human tissues have been discussed (Kobayashi and Kirschvink, 1995). The overall picture is thus a general effect of GMF on life forms.

Life evolved on Earth along changes in the GMF life history. Any other environment lacking a GMF is expected to generate reactions in living organisms. These concerns become urgent questions in light of planned long-term flights to other planets (Belyavskaya, 2004). Understanding GMF effects on life will provide the fundamental background necessary to understand evolution of life forms in our planet and will help us to develop scientific recommendations for design of life-support systems and their biotic components for future space exploration.


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