New England Carnivorous Plant Society

Provoking a Venus flytrap takes a certain amount of finesse. If you brush just one of the trigger hairs inside of its leaves, the plant likely won't react. But if you trigger it again quickly enough, it will spring into action, swinging its famous mouth shut.

Waiting for a double trip probably keeps the plant from wasting energy on raindrops or other things that aren't nutritious flies. But despite centuries of interest in the species, no one was quite certain how the plants remember the first trigger in order to act on a second.

In a paper published last week in Nature Plants, researchers reported they had found the cause: calcium ions. By inducing the flytraps to glow when calcium entered their cells, a team of scientists was able to show how the ions build up as the hairs are triggered, eventually causing the snap.

Calcium is used for conveying information between cells in many different life-forms, said Mitsuyasu Hasebe, the leader of the lab at the National Institute for Basic Biology in Okazaki, Japan, where the research was done. The molecule is normally "scarce in the cell, but abundant out of it," he said, making it easy for cells to recognize and react to changes in concentration.

In 1988, a pair of plant scientists hypothesized that two overlapping rushes of calcium ions might spur the Venus flytrap to close, but had no way to test their idea. More recently, another group of researchers - including Rainer Hedrich, who participated in the new paper - solved part of the puzzle, showing that electrical signals tell the flytrap when its trigger hairs have been pressed. They also speculated that calcium helps the plant keep track.

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The carnivorous plant Venus flytrap (Dionaea muscipula) captures and digests small animals and absorbs nutrients with its characteristic insectivorous leaves. Six sensory hairs on the inner surface of each leaf sense a visiting prey and cause the trap to close. A single contact event with a sensory hair is not sufficient, but a second contact within 30 seconds will induce the trap to close quickly and ensnare the unlucky prey. Thus, Venus flytraps store the memory of the first stimulus for about 30 seconds. But how does a plant memorize anything when it has no brain or nervous system?

In 1988, Dr. Dieter Hodick and Dr. Andreas Sievers from the Botanical Institute at the University of Bonn, Germany speculated that changes in calcium ions might be involved in the memory of the Venus flytrap. However, lacking the technological means to measure calcium concentrations without damaging the cells, they were unable to explore this possibility.

Now, in a study to be published in Nature Plants, a graduate student Mr. Hiraku Suda and Professor Mitsuyasu Hasebe of the National Institute for Basic Biology (NIBB) in Okazaki, Japan, together with their colleagues, have succeeded in visualizing intracellular calcium concentrations in the Venus flytrap and have demonstrated that its short-term memory can indeed be explained by changes in calcium concentration.

The research team first established a genetic transformation method for the Venus flytrap. They then introduced the gene encoding the intracellular calcium sensor protein GCaMP6, which emits green fluorescence when bound to calcium, into the insectivorous plant, allowing them to visualize changes in intracellular calcium concentrations for the first time.

To visualize the flytrap's memory mechanism, Dr. Hasebe and his colleagues spliced a special type of gene into the plant. This gene, widely used in biology, produces a protein that turns fluorescent green when it binds to a target - in this case, a calcium ion.

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