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Geomagnetic Field Effects on Living Systems

 

on plant growth, it was reported that very low MFs less than the GMF were capable of delaying both

organ formation and development of barley (Hordeum vulgare) seedlings (Lebedev et al., 1977). By using

ferromagnetic shields, the infuence of weak, alternating MF, which was adjusted to the “cyclotron fre­

quency” of Ca²⁺ and K⁺, was studied on the fusion of tobacco (Nicotiana tabacum) and soybean (Glycine

max) protoplasts (Nedukha et al., 2007). It was observed that in these conditions protoplasts fusion

increased its frequency two to three times with the participation of Ca²⁺ in the induction of protoplast

fusion (Nedukha et al., 2007). Artifcial shielding of the GMF caused a signifcant decrease in the cell

number with enhanced DNA content in root and shoot of onion (Allium cepa) meristems (Nanushyan

and Murashov, 2001).

Putative magnetoreceptor, CRY was frst found in a fowering plant Arabidopsis thaliana in 1993

(Ahmad and Cashmore, 1993), termed as AtCRY1, which played an important role in photomorpho­

genic responses (Lin and Todo, 2005). Recently, the role for AtCRY1 has been investigated as a candidate

for magnetoreceptor. For example, the growth-inhibiting infuence of blue light on the Arabidopsis is

moderated by MFs in a way that may use the radical pair mechanism (Ahmad et al., 2007). Consistent

with the theoretical framework of the radical-pair mechanism, AtCRY1 has been shown to form mag­

netically sensitive radical pairs afer photoexcitation of a favin adenine dinucleotide (FAD) cofactor

(Maeda et al., 2012). Moreover, the removal of the local GMF negatively afects the reproductive growth

of Arabidopsis, which thus afects the yield and harvest index (Xu et al., 2012, 2013), and delays the

fowering time through downregulation of fower-related genes (Xu et al., 2012; Agliassa et al., 2018a).

Te expression changes of three AtCRY1-signaling related genes, PHYB, CO, and FT, suggest that the

efects of a near null MF are CRY-related, which may be revealed by a modifcation of the active state of

CRY and the subsequent signaling cascade plant CRY has been suggested to act as a magnetoreceptor

(Xu et al., 2012). Artifcial reversal of the GMF has confrmed that Arabidopsis can respond not only to

MF intensity but also to MF direction and polarity (Bertea et al., 2015). Moreover, the GMF was found to

impact photomorphogenic-promoting gene expression in etiolated seedlings of Arabidopsis, indicating

the existence of a light-independent root magnetoreception mechanism (Agliassa et al., 2018b).

With regard to exposure of plants to MFs higher than the GMF, the MFs ranging ~1–30 mT have been

reported to produce changes in quantum yield of favin semiquinone radicals in AtCRY1 (Maeda et al.,

2012). However, most of the attention has been focused on seed germination of important crops like

wheat, rice, and legumes, and many other physiological efects on plants of high MFs described plant

responses in terms of growth, development, photosynthesis, and redox status (Mafei, 2014). Te exami­

nation of the efects of 7 mT SMF combined with 20 kV/m EF on redox status was performed on shallot

(Allium ascalonicum) leaves and the combined exposures increased lipid peroxidation and H2O2 levels

(Cakmak et al., 2012). Hence, the combined exposures have distinct impacts on the antioxidant system

leaves (Cakmak et al., 2012). Photosynthesis, stomatal conductance and chlorophyll content increased

in corn plants (Zea mays) exposed to SMFs of 100 and 200 mT, compared to control under irrigated

and mild stress conditions (Anand et al., 2012). In tomato (Solanum lycopersicum), a signifcant delay in

the appearance of frst symptoms of geminivirus, and early blight and a reduced infection rate of early

blight were observed in the plants from exposed seeds to increased SMFs from 100 to 170 mT (De Souza

et al., 2006).

Mass extinction events profoundly reshaped Earth’s biota during the early and late Mesozoic and

terrestrial plants were among the most severely afected groups (Mafei, 2014). Several plant families

were wiped out, while some new families emerged, and eventually, became dominant (Mafei, 2014). Te

behavior of the GMF during the Mesozoic and Late Paleozoic, or more precisely between 86 and 276.5

Ma, is of particular interest. Its “virtual dipole moment (VDM),” originating from a geocentric dipole,

seems to have been signifcantly reduced (≈ 4 × 1,022 Am²), compared to the present values (Shcherbakov

et al., 2002).

One of the working hypotheses to explain these mass extinctions is the cease of the GMF when the

geomagnetic pole was reversed (Mafei, 2014). Because the GMF strength is strongly reduced during

polarity transitions when compared to stable normal or reversed polarities (Mafei, 2014). It has been