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Venus flytrap

Venus flytraps shown to generate measurable magnetic fields

Image credit: Dreamstime

An interdisciplinary team led by researchers at Johannes Gutenberg Universitaet Mainz in Germany have used atomic magnetometers to measure biomagnetic signals generated by the Venus flytrap.

The Venus flytrap is a carnivorous plant which captures prey with a closing trap formed by its leaves, which is triggered by contact with the tiny hairs on their inner surfaces. During this process, electrical signals trigger the closure of the leaf lobes.

Now, for the first time, scientists have measured the magnetic fields generated by these moving charges. This was made possible using atomic magnetometers.

“You could say that investigation is a little like performing an MRI scan in humans,” said physicist and PhD candidate Anne Fabricant. “The problem is that the magnetic signals in plants are very weak, which explains why it was extremely difficult to measure them with the help of older technologies.”

In the human brain, subtle changes in voltage in certain results arise from concerted electrical activity that travels through nerve cells in the form of action potentials. Techniques such as EEG, MRI, and – increasingly – MEG, can be used to record these activities noninvasively and thus diagnose disorders. Similarly, when plants are stimulated, electrical signals are generated and travel through a cellular network analogous to animal nervous systems. However, while biomagnetism has been well documented in humans and other animals, comparatively little research has been done on biomagnetism in plants.

“We have been able to demonstrate the action potentials in a multicellular plant system produce measurable magnetic fields, something that had never been confirmed before,” Fabricant said.

The Venus flytrap’s leaves close on prey after two successive stimuli; each stimulus triggers an action potential that travels throughout the trap.

The trap is electrically excitable in a variety of ways. In addition to mechanical influences such as touch or injury, osmotic energy (such as saltwater loads) and thermal energy can also trigger action potentials. In this study, the scientists used heat stimulation to trigger action potentials, eliminating mechanical background noise in their measurements.

Previous studies on biomagnetism in plants has been limited to 'SQUID' magnetometers; bulky instruments designed in the 1960s which must be cooled to cryogenic temperatures to take measurements. In this Scientific Reports study, the researchers used atomic magnetometers to measure the magnetic signals. The sensor is a glass cell filled with a vapour of alkali atoms, which react to small changes in the local magnetic field. These magnetometers can be miniaturised and do not require cooling to cryogenic temperatures.

The Venus flytrap produced magnetic signals with an amplitude of up to 0.5 picotesla: “The signal magnitude recorded is similar to what is observed during surface measurements of nerve impulses in animals,” said Fabricant.

Fabricant and her colleagues plan to measure even smaller biomagnetic signals from other plant species. In the future, this noninvasive technique could potentially be used in smart agriculture for crop diagnostics. For instance, it could be used to detect electromagnetic responses to sudden changes in temperature, pest presence, or chemical influences without damaging plants using electrodes.

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