Scientists have genetically modified a Venus flytrap so that it glows green in response to external stimulation and provides important information about the functioning of the plant's short-term memory.
Scientists are continuing to study the mechanisms by which the Venus flytrap can detect when it has caught a tasty insect as prey, as opposed to an inedible object (or just a false alarm). There is evidence that the carnivorous plant has a similar short-term memory, and a team of Japanese scientists found evidence that the mechanism for this memory lies in changes in the concentration of calcium in its leaves, according to a recent article in the journal Nature Plants.
The Venus flytrap attracts its prey with a pleasantly fruity scent. When an insect lands on a leaf, it stimulates the highly sensitive trigger hairs that line the leaf. When the pressure becomes strong enough to bend these hairs, the plant snaps its leaves shut and traps the insect inside. Long cilia grip and hold the insect in place, much like fingers, while the plant begins to secrete digestive juices. The insect is digested slowly over five to 12 days, after which the trap opens again and releases the dried-out shell of the insect into the wind.
As early as 2016, a team of German scientists discovered that the Venus flytrap can actually "count" how often something touches its hair-lined leaves – an ability that helps the plant between the presence of prey and a small nut or stone to distinguish. or even a dead insect. The scientists zapped the leaves of test plants with mechanoelectric impulses of varying intensity and measured the reactions. It turns out that the plant recognizes this first "action potential" but doesn't immediately snap into place and waits for a second zap to confirm the presence of the actual prey. At this point the trap closes.
However, the Venus flytrap does not close completely and produces digestive enzymes to consume the prey until the hairs are triggered three more times (for a total of five stimuli). The German scientists compared this behavior with a rudimentary cost-benefit analysis, in which the number of triggering stimuli of the Venus flytrap helps to determine the size and nutritional content of potential prey in the mouth and to determine whether the effort is worthwhile. If not, the trap releases anything that was caught within a 12 hour or so. (Another means the Venus flytrap uses to tell the difference between an inedible object and actual prey is through a special chitin receptor. Most insects have a chitin exoskeleton, so the plant produces even more digestive enzymes in the presence of chitin.)
The implication is that the Venus flytrap must have a short-term memory mechanism for this to work, as it must "remember" the first stimulation long enough for the second stimulation to register. Previous research has shown shifts in calcium ion concentrations play a role, although the lack of any means of measuring these concentrations without damaging the leaf cells prevented scientists from testing this theory.
Enlarge /. Visualization of the changes in the intracellular calcium concentration of the Venus flytrap using the fluorescent GCaMP6 calcium sensor after stimulation with a needle.
This is where this latest study comes in. The Japanese team figured out how to introduce a gene for a calcium sensor protein called GCaMP6, which glows green when it binds to calcium. This green fluorescence allowed the team to visually track changes in calcium concentrations in response to stimulation of the plant's delicate hairs with a needle.
"I tried so many experiments for over two and a half years, but they all failed," said co-author Hiraku Suda, a graduate student at the National Institute of Basic Biology (NIBB) in Okazaki, Japan. "The Venus flytrap was such an attractive system that I haven't given up. I finally noticed that alien DNA was being integrated into the dark-grown Venus flytrap with great efficiency. It was a small but indispensable cue."
The results support the hypothesis that the first stimulus triggers the release of calcium, but the concentration does not reach the critical threshold that signals the closure of the trap without a second influx of calcium from a second stimulus. However, this second stimulus must occur within 30 seconds as calcium levels decrease over time. If there is more than 30 seconds between the first and second stimuli, the trap will not close. The growth and decrease of the calcium concentrations in the leaf cells seems to actually serve as a kind of short-term memory for the Venus flytrap.
The next step is to study the relationship between calcium levels and the facility's electrical network, which converts the movement of the prey trapped in the trap into small electrical charges that travel across the cells. Scientists already knew that calcium and these electrical signals are closely related in many plants. It is therefore not surprising that the Venus flytrap has a similar connection. What is not clear is exactly how the two systems work together.
"This is the first step in uncovering the evolution of plant movement and carnivore as well as the underlying mechanisms," said co-author Mitsuyasu Hasebe, professor and deputy director general of the NIBB. "Many plants and animals are interesting, but biological peculiarities have not been explored."
DOI: Nature Plants, 2020. 10.1038 / s41477-020-00773-1 (About DOIs).
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