Although it lacks a brain, the carnivorous plant Dionaea muscipula has a functional short-term memory system. Researchers working in plant biology found that not only does the plant better known as the Venus flytrap know when an insect lands inside a leaf, but it can also “remember” when it arrived. Now, according to Nature Plants, genetic modification may have cracked the secret as to how Venus flytraps work.
How Venus Flytraps Work
The Venus flytrap is a well-known carnivorous plant that feeds on insects through its fascinating and complex plant biology. Ars Technica describes how it attracts prey by emitting an attractive fruity scent. When the insect lands on the leaf in search of a possible meal, it stimulates sensory hairs on the plant. In response, the leaf clamps shut, holding the struggling insect closely as glands pour out digestive enzymes. After around 5 to 12 days, the leaf reopens to release the digested husk and begin luring a new meal into its interior.
Leaf closure is quite a sophisticated process. To dine successfully, the plant must control its actions and only snap up prey. Otherwise, every time a raindrop or speck of dirt landed, the leaf would waste precious digestion time.
Venus flytrap leaves are lined with sensory hairs, as Ars Technica points out. When something sizable lands inside the leaf fold, it bends one or more of these hairs. If this is inanimate, like dirt or a raindrop, for example, the sensory hair is only triggered once. However, if it’s an insect, the potential meal will likely move around or struggle to get out, thus bending the sensory hairs more than once.
And somehow, as Harvard University’s Science in the News notes, without a brain or central nervous system, the plant knows how to tell the difference between a meal and accidental touch.
Plant Biology, Calcium and Memory
Plant researchers already knew how Venus flytraps work to control mealtimes, noticing that leaves only closed after a second sensory hair response. According to BBC News, the plant also counts itself through the digestive process once it traps an insect. After two instances triggering the sensory hairs, the leaf increases hormone output. With five activations, the plant releases digestive enzymes, and the leaf changes its structure in order to soak up the digested insect juices.
What researchers did not know was how insect movement initiated this process or how the plant could apparently store short-term memory. They shed light on this quite literally by using genetic modification to light up the plant leaves.
The scientists genetically modified Venus flytrap plants with a gene encoding the intracellular calcium sensor protein GCaMP6, as Phys.org reports. This green fluorescence protein emits light when bound to calcium, making the leaves glow in the dark. Once activated, the green glow can be tracked through the leaf as calcium is released within plant cells.
Using leaves from the genetically modified plants, scientists activated the sensory hairs by poking them with a needle. Simulating the activity of a trapped insect, the team saw a glow of calcium release due to sensory hair activation. When they restimulated the leaf, the glow increased and spread, and if this was done within 30 seconds, the leaf snapped shut.
Along with other experimental approaches, the team concluded that calcium facilitated memory within the leaf. Although one stimulation caused a rise in calcium, only a second one within 30 seconds could push levels high enough to trigger closure.
Innovation From Plant Biology
As Science News notes, this is the first time that calcium has been implicated in this kind of plant response. Being able to tell that something landing on a leaf is a potential meal saves valuable time, resources and energy for the Venus flytrap.
Furthermore, it’s a step closer to understanding short term memory in plants. Long-term memory exists in many species — like how a carrot crop focuses on growing roots in its first year and then flowers for seed production in its second year. Or the process by which a plant “remembers” to flower in the spring — also known as vernalization.
Understanding calcium mechanisms in plant biology may also be valuable for technological innovation in robotics and in data storage systems. Science Focus describes how mammalian brains form memory in the hippocampus; knowing how calcium or other electrolyte surges influence short-term memory systems could help to build or understand alternative storage systems.
Researchers have also been experimenting with Venus flytrap leaves in robotics, using them in biohybrids for grabbing delicate objects. Science News describes how scientists attached electrodes to Venus flytrap leaves, which they then triggered to catch tiny falling weights or wires successfully. Soft actuators or biohybrid models could help to develop better systems for prosthetics, for example, or lead to more delicate automated handling in other industrial processes.
It turns out there’s a lot we could learn from continuing to study how Venus flytraps catch a meal.
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