Magnetotropism

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Magnetotropism is the movement or plant growth in response to the stimulus provided by the magnetic field in plants (specifically agricultural plants) around the world. As a natural environmental factor in the Earth, variations of magnetic field level causes many biological effects, including germination rate, flowering time, photosynthesis, biomass accumulation, activation of cryptochrome, and shoot growth. [1]

Contents

Biological effects

As an adaptive behavior, magnetotropism is recognizing as a method to improve agriculture success, using the well-studied plant model, Arabidopsis thaliana, a typical small plant which is native in the Europe and Asia with well-known genomic functions. In 2012, Xu et al. conducted a Near-Null Magnetic Field experiment under white light and long-day conditions using the homemade equipment of combining three couples of Helmholtz coils in vertical, north–south, east–west direction compensating near-null magnetic field. Xu noted that under the near-null magnetic field, Arabidopsis thaliana delays the flowering time by altering the transcription level of three cryptochrome related florigen genes:PHYB, CO, and FT; Arabidopsis thaliana also induced longer hypocotyl length under white light in the Near-Null magnetic field compared to standard geomagnetic field and either dark or white light conditions. [2] Furthermore, the biomass accumulation reduces in the near-null magnetic field while Arabidopsis thaliana switches from vegetative growth to reproductive growth. [3] Not until recently, Agliassa conducted a similar experiment continuing Xu et al. ’s discovery found out that Arabidopsis thaliana delay flowering by shortening stem length and reduction of leaf size. This expression shows that the near-null magnetic field has caused downregulation of several flowering genes, including FT genes in the meristem and leaves, which is cryptochrome related. [4]

Physiological mechanism

Although preliminary experiments have shown a wide range of effects due to the magnetic field, the mechanism has not yet been elucidated. Having known that the delay of flowering is downregulating in cryptochrome related genes affected by the near-null magnetic field under blue light, cryptochrome is taking as a potential magneto-sensor by a few considerations. Based on the radical pair model, cryptochrome would be the magneto-sensor in the light-dependent magnetoreception since cryptochrome has evolved a significant role of plant behavior, including blue-light reception and regulation, de-etiolation, circadian rhythm, and photolyase. [5] In the photoactivation process, blue light hits cryptochrome and accepts a photon to Flavin while tryptophan receives a photon by another tryptophan donor simultaneously. Due to the geomagnetic field, this combination would rotate from south pole to north pole of the Earth and convert the two single photons back to its inactive resting states under aerobic environment. [6] Based on a few behavior changes due to variations of the magnetic field, many plant scientists have paid attention to cryptochrome being the candidate for the magneto-sensory receptor. So far, the interactions between signals and magnetoreceptor molecules have not yet discovered, thus leaving potential space for future research while understanding magnetotropism would be significant for improving life forms and ecology such as agriculture.

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EARLY FLOWERING 3 (ELF3) is a plant-specific gene that encodes the hydroxyproline-rich glycoprotein and is required for the function of the circadian clock. ELF3 is one of the three components that make up the Evening Complex (EC) within the plant circadian clock, in which all three components reach peak gene expression and protein levels at dusk. ELF3 serves as a scaffold to bind EARLY FLOWERING 4 (ELF4) and LUX ARRHYTHMO (LUX), two other components of the EC, and functions to control photoperiod sensitivity in plants. ELF3 also plays an important role in temperature and light input within plants for circadian clock entrainment. Additionally, it plays roles in light and temperature signaling that are independent from its role in the EC.

References

  1. ↑ Maffei, Massimo (4 September 2014). "Magnetic field effects on plant growth, development, and evolution". Frontiers in Plant Science. 5: 445. doi: 10.3389/fpls.2014.00445 . PMC   4154392 . PMID   25237317.
  2. ↑ Xu, Chunxiao (1 March 2012). "A near-null magnetic field affects cryptochrome-related hypocotyl growth and flowering in Arabidopsis". Advances in Space Research. 49 (5): 834–840. Bibcode:2012AdSpR..49..834X. doi:10.1016/j.asr.2011.12.004.
  3. ↑ Xu, Chunxiao (September 2013). "Removal of the local geomagnetic field affects reproductive growth in Arabidopsis". Bioelectromagnetics. 34 (6): 437–442. doi: 10.1002/bem.21788 . PMID   23568853 . Retrieved 6 June 2019.
  4. ↑ Agliassa, Chiara (July 2018). "Reduction of the geomagnetic field delays Arabidopsis thaliana flowering time through downregulation of flowering‐related genes". Bioelectromagnetics. 39 (5): 361–374. doi:10.1002/bem.22123. PMC   6032911 . PMID   29709075.
  5. ↑ Vanderstraeten, Jacques (14 February 2018). "Low-Light Dependence of the Magnetic Field Effect on Cryptochromes: Possible Relevance to Plant Ecology". Frontiers in Plant Science. 9: 121. doi: 10.3389/fpls.2018.00121 . PMC   5817061 . PMID   29491873.
  6. ↑ Maeda, Kiminori (27 March 2012). "Magnetically sensitive light-induced reactions in cryptochrome are consistent with its proposed role as a magnetoreceptor". Proc Natl Acad Sci U S A. 109 (13): 4774–9. Bibcode:2012PNAS..109.4774M. doi: 10.1073/pnas.1118959109 . PMC   3323948 . PMID   22421133.
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