Venus Flytrap Generates Magnetic Fields01/25/2021
The carnivorous Venus flytrap can generate magnetic fields that are almost as strong as those in humans. Researchers from Mainz and Würzburg have demonstrated this with a new, non-invasive measuring technique.
The Venus flytrap Dionaea muscipula has been intensively studied at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, for about ten years. Since then, the team led by biophysicist Professor Rainer Hedrich has repeatedly succeeded in gaining new, groundbreaking insights into the secret life of this carnivorous plant.
In their most recent paper in the journal Scientific Reports, the JMU group, together with researchers from Johannes Gutenberg University Mainz, Helmholtz Institute Mainz and Physikalisch-Technische Bundesanstalt Berlin, demonstrates that the electrically excitable Venus flytrap can also generate magnetic fields. To be able to measure these fields, some tricky challenges had to be overcome.
Electrical signals, also called action potentials, are used by the Venus flytrap to detect prey and transmit stimuli. This works very similarly to the transmission of information in the neuronal networks of humans. Only with the help of the fast electrical impulses the trap can snap at high speed. This enables it to trap flies that are difficult to catch even for humans.
Medical detector made useful for plants
In the human brain, electrical nerve impulses generate magnetic fields. Neurologists exploit this to monitor the activity of certain areas of the brain: In magnetoencephalography (MEG), patients are examined in the "tube". The electrical nerve impulses of their brain and the correlated magnetic fields are displayed three-dimensionally.
These biomagnetic fields are extremely weak; with an amount to only a few femto Tesla. This makes them about a hundred billion times weaker than the Earth's magnetic field. Extremely low temperatures are needed to detect these weak fields: the detectors need to be cooled down to -269 °C with liquid helium.
In the Venus flytrap, the physicists from Mainz expected electromagnetic signals to be just as weak or even weaker. That's why they conducted their experiments at the Physikalisch-Technische Bundesanstalt in Berlin. There, a specially shielded experimental room protects the setup from external interfering signals.
Trap immobilised and action potentials triggered without contact
Before they could examine the Venus flytrap, however, there were technical hurdles to overcome. "During the examination in the tube, no movement is allowed because otherwise the measurement will not work," explains JMU researcher Dr. Sönke Scherzer. So how can you study a process there in which movement is essential to evoke the action potentials? In general mechanical stimulation of the trap´s sensory hairs initiates the electrical signalling leading to trap closure.
"We solved the problem by immobilising the trap," says Scherzer. "We also had to find a contact- and interference-free method to trigger the action potentials. That was not easy because even minimal disturbances from outside falsify the measurements," reports Rainer Hedrich. "But we knew that action potentials can also be triggered by applying heat. So we increased the temperature step by step. At the critical threshold of 34 °C, the trap began to spontaneously fire action potentials without moving."
Novel miniaturised magnetic field detectors
Now the PhD student and first author of the paper, Anne Fabricant, who is researching in the team led by Mainz nuclear physicist Professor Dmitry Budker, was able to trigger action potentials without interference and analyse the biomagnetic signals that occurred. For this purpuse, new types of miniaturised magnetic field detectors were used, which are adapted to the size and biology of the Venus flytrap and which - unlike their medical predecessors – do not need to be cooled.
"We were all amazed when Anne was able to record magnetic fields similar to those of human nerves," Scherzer recounts. In the future, this new non-invasive technique could be used to work out common principles and differences in electrical signal transmission in animals and plants. It is also conceivable to use mobile MRI devices for quick and contactless detection of stress in crop plants caused by factors like heat, drought or nutrient deficiency.
Fabricant, A., Iwata, G.Z., Scherzer, S. et al.: Action potentials induce biomagnetic fields in carnivorous Venus flytrap plants, Sci Rep 11, 1438 (2021), Open Access: https://doi.org/10.1038/s41598-021-81114-w
Prof. Dr. Rainer Hedrich, Chair of Botany I (Plant Physiology and Biophysics), University of Würzburg, T +49 931 31-86100, firstname.lastname@example.org