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Experiment: Venus Fly Trap Electrophysiology

The electrical impulse is not only relegated to the hearts, muscles, and brains of animals. Plants use it too to communicate with various parts of itself. Here we will use a beautiful plant that Darwin himself called "one of the most wonderful in the world": the Venus Fly Trap.

Time 1 hour
Difficulty Intermediate

What will you learn?

With this experiment, you can learn about plant electrophysiology and record the action potential of the Venus fly trap.

Prerequisite Labs


Background

A nervous system allows you to sense and respond quickly to the environment around you. Animals have them, but plants do not. But not having a nervous system does not mean you cannot sense and respond to the world. Plants can certainly sense the environment around them and move. You have seen your plants slowly turn their leaves towards sunlight by the window over a week, open their flowers in the day, and close their flowers during the night. Some plants can move in much more dramatic fashion, such as the Venus Fly Trap and the Sensitive Mimosa.

The Venus Fly Trap comes from the swamps of North Carolina, USA, and lives in very nutrient-poor, water-logged soil. For this, it traps and eats insects to extract the nitrogen and phosphorous needed to form amino acids, nucleic acids, and other molecules (as it is a plant, it can still photosynthesize carbohydrates and make it's own food, using the sun and carbon dioxide).

If you look closely at the Venus Fly Trap, you will notice it has very tiny "Trigger Hairs" inside its trap leaves.

If an insect touches a trigger hair, an action potential occurs in the leaves. This is a different action potential than what we are used to, as it's based on the movement of calcium, potassium, and chloride ions (vs. movement of potassium and sodium as in the action potentials of neurons and muscles), and it is muuuuuuuuucccchhhhhh longer than anything we've seen before.

If the trigger hair is touched twice within 20 seconds (two action potentials within 20 seconds), the trap then closes. The trap is not closing due to muscular action (plants do not have muscles), but rather due to a an osmotic, rapid change in the shape of curvature of the trap leaves. Interestingly, the firing of action potentials is not always reliable, depending on time of year, temperature, health of plant, and/or other factors. Quite different from we humans, action potential failure is not devastating to a Venus Fly Trap.

We can observe this plant action potential using our Plant SpikerShield Amplifier. Welcome to the Brave New World of Plant Electrophysiology.

Downloads

Before you begin, make sure you have the Backyard Brains Spike Recorder and Arduino Programs installed on your computer. The Arduino "Sketch" is what you install on your Arduino circuit board using the Arduino laptop software (your board comes preinstalled if you bought the Arduino from us), and Backyard Brains Spike Recorder program allows you to visualize and save the data on your computer when doing experiments. We made a software video for you to explain this!

Tutorial Video of Experiment

Recorded partly on location in August 2014 at the Marine Biological Laboratory in Woods Hole, Massachusetts. Thanks to the 2014 Methods in Computational Neuroscience course for inviting us to teach and do some new experiments. The video below is an updated December 2015 version.

Procedure

In this experiment, we are going to measure the action potentials generated by plant cells.

  1. You can use our preassembled Plant SpikerShield Bundle which has all the materials you need (sans plant), including our modified amplifier that has lower frequency filter settings (0.6 - 129 Hz) and lower gain (20-100x) to record the Fly Trap Action Potential.
  2. Find a Venus Fly Trap. You can generally find them in museum science stores, but our favorite online supplier is Peter D'Amato's ""California Carnivores" store. If you live in Ann Arbor, MI, you can conveniently purchase them at Downtown Home & Garden
  3. Select an open trap you want to record from, and place a little bit of conductive electrode gel on the side of the same trap. Using our manipulator, position your silver wire electrode onto the side of same trap, inserting the electrode into the blob of EMG electrode gel..
  4. Put the ground wire needle in the.....ground of the plant.
  5. Open up our Spike Recorder program, and you should see a moving yellow line moving. Zoom in or out of the y-axis by clicking on the + o - signs on the center left side of the screen, and you can zoom in or out on the time scale (x-axis) with the scroll wheel on your mouse or two finger motion on your trackpad.
  6. In the settings window (click on the gear shaped symbol in the upper left hand of the screen), connect to your USB port ("the plug button")
  7. Now, the line on your screen should become flat, we are recording from the plant. Please the "Record" button (red button on top right of screen) to save your data as a .wav file.
  8. With a plastic probe, carefully touch one of the trigger hairs. In the SpikeRecorder software, you should notice a long deflection...Congratulations, you have just recorded an action potential in plants. Such a universal signal that keeps us all functioning.
  9. if your action potential is too big, resulting in "flat tops," your gain is too high and you need to reduce it on the SpikerShield. The SpikerShield has gain wheel that can appear counter-intuitive, as counterclockwise movement increases gain but clockwise movement decreases gain. We have found one quarter gain works well.
  10. If you want to see an action potential again, wait approximately 20-30 seconds before touching the trigger hairs again, or else the trap will close, and "no more spikes for you. You will either have to move to a different open trap, or wait 1-2 days for the trap to open again...
  11. To analyze the data (the duration of the plant action potential), time between action potentials, etc., you can open your .wav files by clicking the "open button" (looks like three vertical lines) next to the "record button."
  12. Congratulations! You have just recorded your first plant spike! Now investigate further!

Discussion / Further Work

  • Many plants fire action potentials, not just the plants that dramatically move like the Venus Fly Trap or the Sensitive Mimosa. There exists a whole field of study called "plant electrophysiology." A recent paper in Nature found electrical potential propagation along a plant in response to injury on one leaf. This field of is still rather small with only a handful of scientists actively engaged in it; there is plenty of room for new discoveries.
  • You have noticed that the action potential propagation sometimes doesn't occur. You can measure this as a function of temperature, time of year, etc. Also, how does the shape of the action potential vary from plant to plant, from trap to trap? Does the 20 clock change as a function of temperature as well? Does the time course of the action potential change as the plant ages? Many questions we have.
  • We prefer Venus Fly Trap varieties that have the traps resting on the soil. When you are trying to record from a trap on a long stem, hanging in the air, the touching of the trigger hair will cause the whole trap to sort of "wobble" which can disturb the electrode interface and cause the action potential shape to be distorted. The B-52 variety works well for electrophysiology.
  • The figures above are normalized so that the baseline is 0 mV, but the plant probably has a resting membrane potential, how would we go about measuring this?
  • Finally, we emphasize plant physiology is new to us. We are not plant experts (the last time we formally studied botany was in high school). If you have corrections/commentary, please do e-mail us your thoughts as we continually improve these write-ups based on your feedback!