CORNELL (US) — When faced with barriers, like a patch of stiff dirt, some roots form helical spring-like shapes, time-lapse images show.
Surprisingly, this root geometry is largely the result of mechanics—the same mechanics that determine the stability of beams in buildings, researchers say.
When the roots run into barriers, growth causes compression and eventual buckling. The root senses this obstruction and responds by twisting the root tip. The effects combine to give the root a helical geometry.
From insights gleaned through mathematical modeling, researchers speculate that the roots are pushing off their environment to get an increased force at their tip, an effect that is enhanced by twisting.
Staining the roots and imaging them on a confocal microscope reveals that the roots twist around their axes in the helical region but remain untwisted throughout the rest of the root. Further experiments show that this twisting is a biological response of the root induced by longitudinal forces. (Credit: Cornell)
“Evolutionarily speaking, this twisted buckling mechanism improves the fitness of the plant by allowing it to pass through barriers and explore more of its environment,” says Cornell University graduate student Jesse Silverberg, first author of a paper published in the Proceedings of the National Academy of Sciences.
The discoveries were made in the lab of Itai Cohen, associate professor of physics; the novel experimental setup was conceived several years ago by co-author and former graduate student Sharon Gerbode. The team collaborated with Maria Harrison of the Boyce Thompson Institute for Plant Research, to develop a 3D laser sheet imaging technique for recording plant root growth.
The setup consists of a laser sheet that illuminates a plane inside a transparent box, which is filled with a dense, translucent gel that acts as the “soil” for the roots. A camera takes a series of images as the box moves through the laser sheet, which effectively scans its contents.
Using software, the researchers reconstructed 3D images of how the roots of the legume Medicago truncatula responded to barriers of different stiffness.
The study could eventually assist in breeding crop plants optimized for growth in areas where climate change or over-farming has led to difficult soil conditions, Harrison says.
“There is a growing community of people trying to trace macroscopic morphologies to microscopic mechanics,” Cohen says. “The idea is that mechanics plays an important role in growth—it’s not just genetics, but you have physical things that can produce these types of variations and morphologies, and we see this as an important step forward.”
The work was supported by the National Science Foundation, Cornell’s IGERT Program in Nonlinear Systems and the U.S. Department of Energy.
Source: Cornell University