By Hero Winsor
If you’ve ever been to the lab buildings on campus, you’ll know how much of a liminal space it is. Going down to the basement this is amplified. The long 70s corridors lead you down a hallway with hanging prints from the printmaking studio in lab II. The HVAC whirs as you seem to pass into another world. If you’re entering the building when the labs were still dethawing from quarantine, you might be the first to activate the motion detecting lights. A little further down in one of the lab spaces are plants growing. Very special plants it seems, plants that can learn!
Mimosa pudica, otherwise known as touch-me-not or shameplant, reacts to potentially dangerous stimuli by folding up its leaves. Even a light touch can cause them to recoil. What’s interesting is that these plants eventually will stop reacting if the stimulus is repeated enough times. This could be marked down to simple fatigue: the plant has stopped reacting because it lacks the energy to do so, however given a distinct stimulus, it reacts the same as it had before. It has habituated to the stimulus, recognizing it as non-threatening. This is especially extraordinary in that plants do not have a nervous system. In humans and other innervated animals, habituation occurs in our neurons. If a connection between a sensory input and a given response is not useful, after repeated exposure, receptors will begin to shift away from that synaptic connection. In the opposite circumstance, receptors inside the cell will actually join in, strengthening the connection. This allows for faster connections for useful reactions such as running from danger. It also prevents a waste of energy from responses such as running from the squirrels in the trash bins. Plants do not have neurons, so how is Mimosa pudica able to habituate?
I interviewed recent alumni Skyler Webb, who with a lab partner sought out to find if there was a genetic difference in plants that had habituated to stimuli versus plants who had not been habituated. Working under the guidance of neurobiology faculty Dr. Murray, Skyler continued the research that had been put on hiatus because of the pandemic. Skyler approached Nancy Murray as he wanted research experience and more upper division science as the pandemic had made that pretty much impossible. Much of the experiment had to be revised. Originally the apparatus utilized a minicomputer called a raspberry pi but they were unable to get it to work. Of course, the plants had to be grown again, which leads us to the basement.
Twelve touch-me-nots were grown in a humidified environment, given 12 hours of light and 12 hours of darkness. There were setbacks such as losing weeks of work from the humidifier being accidentally turned off. Despite this and other challenges from researching fresh out of quarantine, the plants were eventually ready to test. According to Skyler, the most interesting part of constructing the research was creating the habituation apparatus. The research team was able to use a fan to cause the plant to close its leaves. The fan was set to a timer to go off every 15 minutes. Using the time lapse feature on an old cell phone, they were able to see when the plant had fully habituated. Samples were taken from both the habituated and unhabituated plants.
The genetic component of the research focused on what is called a cDNA library. cDNA, or complementary DNA, is a copy of an mRNA sequence. While cDNA doesn’t have the regulatory sequences of a genomic library, cDNA libraries are useful to discover the codes of genes being expressed by the organism. By using a cDNA library, the hope was to be able to see if different genes were being expressed by the habituated plant. This part of the research is ongoing as Nancy Murray recently got funding for a MinIon DNA sequencer. The device itself is smaller than a cell phone but can sequence at an incredible pace. With this new technology, Nancy has been using her sabbatical to continue the research. Skyler Webb has since graduated and is currently working to enter the Masters in Teaching program. He looks back on this project with fondness and encourages those interested in research to talk to their professors. Evergreen Eye on Science will update on this research when results are available. If you have any groovy research you’ve been doing or planning, and maybe next time, the eye will be on you!
