Call them plant motors. Or plant muscles. Tiny bulges of specialized cells in a mimosa plant can fold its feathery leaflets together in seconds, then relax — and do it again.
A new look at these bulges on the Mimosa pudica plant has revealed more details of how a leaf manages its unusually fast folding, says biomechanist David Sleboda of the University of California, Irvine. “I think that these particular organs are really cool because their motion is reversible,” he says. “[W]hen people see plant motion that is reversible, it feels much more similar to animal motion.”
Scientists have already worked out the basic chemistry that drives a little mimosa motor, or pulvinus, he and colleagues write in a paper slated for the Feb. 6 Current Biology. When a deer hoof or something else scary jostles a leaf, potassium and some other ions shift from one part of a pulvinus toward another. Water follows the swoosh of ions. Cells that lose water deflate and sag while those on the other side bloat. Distortions in multiple pulvini make the halves of a feathery leaf fold toward each other, like an invisible hand gently closing a book.
Instead of studying chemistry, Sleboda and colleagues looked at microscopic structural details in pulvinus cells that help create such useful distortions, he reported January 7 at the annual meeting of the Society for Integrative and Comparative Biology in Austin, Texas. One feature that makes plant-muscle cells bloat more efficiently is reinforcement with microscopic fibrils. They work like corsets, keeping cells from bulging out in all directions. Instead, the corset directs much of the swelling along the axis that will fold up the leaf halves.
Also, pulvinus cells that need to bulge fast have what look like wrinkles of easily expandable tissue for inrushing water, plus special highly porous zones called pit fields. The pits look as if water could sluice through easily in a tickled-leaf emergency. Cell arrangement itself looks specialized for expanding and shrinking. A pulvinus cross section reveals a pattern “like the bellows of a concertina,” Sleboda said.
Post from www.sciencenews.org
As accomplished scientists continue to make groundbreaking discoveries, it is becoming apparent just how complex and fascinating the natural world can be. A sterling example of this is found in the unique way certain plants, such as the mimosa, fold up their leaves in response to external stimuli. To explain this phenomenon, scientists have studied the incredible ‘muscles’ that plants possess in order to understand how they can achieve such swift action.
The movement of the mimosa is achieved through a motor-like process of folding up its leaves that occurs when the plant is disturbed, or ‘tickled.’ This response can be achieved in less than one-tenth of a second, a speed that is achieved by the presence of a succulent type of muscle fiber known as the nyctinastic muscle. This muscle type is contracted by a signal sent to it from the plant’s sensitive cells, which then cause its two major components, the cytoskeleton and the cellulose microfibrils, to interact in order to fold up the leaves.
In addition to the mechano-chemical nerves and the muscles that propel the folding, the mimosa also contains an ion-flux mechanism which is essential in enabling it to cause a response within the plant’s leaves. This ion-flux mechanism works by admitting or releasing ions such as potassium, calcium, and magnesium depending on the plant’s external stimuli, thus stimulating the folding process.
The mimosa plant’s impressive, speedy folding response is a marvel of nature and a testament to the power of the human mind, which was able to uncover the complex operations at work in order for us to better understand why it happens. This type of research is invaluable in furthering our knowledge of the natural world and in allowing us to better understand how plants can be so responsive to their environment.