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Bioelectromagnetism

infuencing both root ion uptake and ion channel activity (Narayana et al., 2018; Islam et al., 2020a).

Similar results have been obtained in Arabidopsis and other plant species (Rakosy-Tican et al., 2005;

Xu et al., 2015, 2017; Azizi et al., 2019; Jin et al., 2019; Pooam et al., 2019; Radhakrishnan, 2019). More

recently, we carried out a time-course microarray experiment to identify genes that are diferentially

regulated by the GMF in shoot and roots. We found that the GMF regulates genes in both shoot and

roots, suggesting that both organs can sense the GMF. However, 49% of the genes were regulated in a

reverse direction in these organs, meaning that the resident signaling networks defne the up- or down-

regulation of specifc genes. Te set of GMF-regulated genes strongly overlapped with various stress-

responsive genes, implicating the involvement of one or more common signals, such as reactive oxygen

species, in these responses. Te biphasic dose response of GMF-responsive genes indicates a hormetic

response of plants to the GMF (Paponov et al., 2021). Terefore, plants can sense and respond to the

GMF using the signaling networks involved in stress responses.

In this chapter, I will highlight some of the basic mechanisms proposed to be involved in plant mag­

netoreception and summarize the plant responses to varying MF intensities both dependent and inde­

pendent from the presence of light.

5.2 Mechanism of Magnetoreception in Plants

Tree diferent mechanisms of magnetoreception have been described: a mechanism involving radical

pairs (i.e., magnetically sensitive chemical intermediates that are formed by photoexcitation of crypto­

chrome (Guo et al., 2018)), which has been demonstrated both in animals (Hore and Mouritsen, 2016)

and in plants (Pooam et al., 2019); the presence of MF sensory receptors present in cells containing fer­

romagnetic particles, as has been shown in magnetotactic bacteria (Kornig et al., 2014); and the detec­

tion of minute electric felds by electroreceptors in the ampullae of Lorenzini in elasmobranch animals

(Kempster et al., 2012).

Of the three possible mechanisms of magnetoreception, only the radical pair mechanism of chemi­

cal magnetosensing adequately explains the alterations in the MF by the rates of redox reactions and

subsequently altered concentrations of free radicals and ROS observed in plants, animals, and humans

(Bertea et al., 2015; Pooam et al., 2019, 2020b; Albaqami et al., 2020). Te theory underlying the radi­

cal pair mechanism predicts that MFs similar in strength to the GMF are too weak to trigger cellular

biochemical reactions; however, these MFs are able to interact with short-lived reaction intermediates

that afect the reaction rates of biochemical reactions. Examples include photoreceptors (e.g., crypto­

chromes) and redox reactions that can be initiated by metabolic factors. Tis modulation of crypto­

chrome signaling and/or redox reactions can alter ROS synthesis in the cells (Pooam et al., 2020a).

5.2.1 The Radical-Pair Mechanism

Spin interactions have profound efects on chemical reactions despite the energies involved are orders

of magnitude smaller than the thermal energy, kBT (Hayashi, 2004). It is known that applied MFs and

magnetic isotope substitution can alter the rates and product yields of free-radical reactions with the

formation of transient paramagnetic intermediates in non-equilibrium electron spin states. Te most

common sources of spin-chemical efects are organic radical pairs (RPs). Typically formed in a singlet

(S) or a triplet (T) state by a reaction that conserves electron spin, RPs interconvert coherently between

their S and T states as a result of the Zeeman, hyperfne, exchange, and dipolar interactions of the elec­

trons and the nuclear spins to which they are coupled (Hore et al., 2020). Applied MFs alter the extent

and timing of the S ↔ T interchange and hence the yields of products formed spin-selectively from the

S and T states (Jones, 2016).

A typical situation considered in the RP mechanism (RPM) is the production of a spin-correlated RP,

let us assume from an electronically excited triplet state, yielding an RP with initially parallel electron

spins. Te spin motion is visible in the vector representations of the RP spin states shown in Figure 5.1.