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Magnetoreception in Plants

in close association with the favin cofactor. Terefore, the possibility of the third-party cellular factors

participating in the formation of RPs during the process of cryptochrome favin reoxidation cannot be

excluded (Pooam et al., 2019). In sum, there are at least two reaction steps in the course of cryptochrome

photocycle that could in principle be altered by the magnetic felds: the step of favin photoreduction and

that of favin reoxidation. In either case, the efect of the magnetic feld would be to alter cryptochrome

biological activity by changing the rate of formation of the active state (forward reaction) or the rate of

disappearance of the active state (reoxidation reaction) (Pooam et al., 2020a).

Te GMF was also found to impact photomorphogenic-promoting gene expression in etiolated seedlings,

indicating the existence of a light-independent magnetoreception mechanism. In Arabidopsis in the absence

of light, the most highly regulated gene in response to MF changes is NDPK2 (Agliassa et al., 2018b), which

is involved in the oxidative stress signaling (Kim et al., 2011). Tis result clearly implies the presence of a

light-independent root magnetoreception mechanism that involves an oxidative response. Tese results are

in agreement with previous studies on GMF reversal (Bertea et al., 2015). Root light-independent responses

to MF variations have been demonstrated in plants under a continuous high gradient MF application, with

a magnetophoretic plastid displacement and a consequent induction of root curvature (Kuznetsov et al.,

1999). Terefore, these results indicate the possibility of a light-independent magnetoreception mechanism

and further studies are necessary to better understand how roots are involved in magnetoreception.

Te rhythmic expression of Arabidopsis clock genes was diferent under GMF with respect to NNMF

under free rhythm running conditions in continuous darkness. Te switching to free-running con­

ditions under continuous darkness caused the internal clock oscillator resetting to its natural period

length. Terefore, the GMF seems not to give any temporal signal to Arabidopsis clock under continu­

ous darkness, thus excluding the GMF infuence on the internal clock period as reported in animals

(Bliss and Heppner, 1976). On the other hand, NNMF treatments showed that the internal clock gene

amplitude was signifcantly (p < 0.05) diferent with respect to plants exposed to local GMF conditions,

regardless of the light presence. Even though exposure to continuous darkness is known to reduce the

amplitude of the clock rhythm (Salome et al., 2008), this was not observed for LHY (Figure 5.12b) and

PRR7 (Figure 5.12d) under NNMF (Figure 5.12). Results exclude a possible role of the GMF as a ZT to

Arabidopsis clock under continuous darkness and highlight the impact of NNMF on Arabidopsis clock

gene amplitude, regardless of the presence of light. Dhiman and Galland (2018) have recently demon­

strated that MF intensities from GMF to NNMF modulate Arabidopsis seedlings gene expression under

both light and dark conditions. Furthermore, NNMF intensities can produce nonspecifc biological

efects on gene expression by afecting RNA polymerase rotation (Binhi and Prato, 2018).

FIGURE 5.12 Time course of LHY, PRR7, and GI relative expression in Arabidopsis thaliana grown under GMF

and NNMF in continuous darkness (CD). LHY (A) and PRR7 (B) under CD conditions show increased gene expres­

sions when exposed to NNMF, with respect to GMF. GI (C) shows a reduced gene expression under NNMF when

compared to GMF. In all plots, white boxes indicate the light phase, whereas black boxes indicate the dark phase.

(Modifed from Agliassa and Mafei (2019).)