Magnetoreception in Arabidopsis thaliana : Effects of geomagnetic fields on transcription and translation

Very little is known about the effects of geomagnetic fields on plants. The present work was undertaken to answer the question whether plants can perceive the geomagnetic fields (Galland and Pazur 2005). Our findings show that the effects of magnetic fields on various responses in Arabidopsis thaliana result in a characteristic multi-peaked pattern in the stimulus-response curves with multiple maxima (peaks) and minima (valleys). These multi-peaked stimulus-response curves display a unique phenomenon in biology. They are distinctively different from the stimulus-response curves, observed in plant physiology, showing a pattern of rising exponential functions, with a plateau finally. The magnetic response also depended upon the fluence rate of the overhead light, the responses being higher at higher fluence rates. However, the magnetic fields apparently are able to manifest their effects even in darkness. The two double mutants displayed variations in their response to magnetic fields, as compared to Ler seedlings, although the basic pattern of effects remained the same. Additionally the effects were enhanced in phyAphyB double mutants as compared to cry1cry2 double mutants indicating suppression of cryptochrome-mediated magnetic effects by phytochromes. These stimulus-response curves are difficult to explain on the basis of the criteria required by the radical-pair model. The effects of magnetic fields were observed not only in darkness but also in cry1cry2 double mutants. Experiments also revealed responses of the Arabidopsis seedlings to magnetic fields even under red light. Interestingly our data are in good correlation with data obtained by Binhi (2001) while working on DNA of E. coli. They got similar stimulus-response curves with similar peak positions as have been observed by us. Binhi and coworkers explained their observations in the theoretical framework of the “ion-interference mechanism”. A comparison of the effects of magnetic fields of the various organizational levels of Arabidopsis plant, i.e., on hypocotyl length, anthocyanin accumulation, abundance of specific mRNA‟s and proteins reveal maximum effects on gene transcription (12-fold approx.), which were reduced to about 6-fold in case of anthocyanin accumulation and were further reduced to only about 2.5-fold in case of suppression of hypocotyl length by blue light in Arabidopsis. We, therefore state that the effects at transcriptional level get balanced out at higher levels of organization (biochemical pathway, growth response) in order to provide “Magnetohomeostasis”