A WUSTL scientist is learning how plants sense touch, gravity and other physical forces

“Picture yourself hiking through the woods or walking across a lawn,” says Elizabeth Haswell, PhD, assistant professor of biology in Arts & Sciences at Washington University in St. Louis. “Now ask yourself: Do the bushes know that someone is brushing past them? Does the grass know that it is being crushed underfoot? Of course, plants don’t think thoughts, but they do respond to being touched in a number of ways.”

“It’s clear,” Haswell says, “that plants can respond to physical stimuli, such as gravity or touch. Roots grow down, a ‘sensitive plant’ folds its leaves, and a vine twines around a trellis. But we’re just beginning to find out how they do it,” she says.

In the 1980s, work with bacterial cells showed that they have mechanosensitive channels, tiny pores in the cell’s membrane that open when the cell bloats with water and the membrane is stretched, letting charged atoms and other molecules rush out of the cell. Water follows the ions, the cell contracts, the membrane relaxes, and the pores close.

Genes encoding seven such channels have been found in the bacteriumEscherichia coli and 10 in Arabidopsis thaliana, a small flowering plant related to mustard and cabbage. Both E. coli and Arabidopsis serve as model organisms in Haswell’s lab.

She suspects that there are many more channels yet to be discovered and that they will prove to have a wide variety of functions.

Recently, Haswell and colleagues at the California Institute of Technology, who are co-principal investigators on an National Institutes of Health (NIH) grant to analyze mechanosensitive channels, wrote a review article in order to “get their thoughts together” as they prepared to write the grant renewal. The review appeared in the Oct. 11 issue of Structure.

Swelling bacteria might seem unrelated to folding leaflets, but Haswell is willing to bet they’re all related and that mechanosensitive ion channels are at the bottom of them all. After all, plant movements — both fast and slow — are ultimately all hydraulically powered; where ions go the water will follow.

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