Watch live plant cells build their cell walls

For the first time, high-resolution time-lapse videos of tiny bits of living plants show how they assemble their protective cell walls, researchers report March 21 in Science Advances. The image sequences provide new insights into how this cell structure forms, which could lead to innovations in plant-derived products such as renewable biofuels.

Cell walls are made mostly of cellulose, a chain of sugar molecules. “Cellulose is the most abundant organic [compound] on the planet,” says bioengineer Shishir Chundawat of Rutgers University in Piscataway, N.J. But “we still don’t know how it’s synthesized.”

Scientists want to understand how cellulose is made not only because it’s useful for many human-made materials including paper and cloth, but also so it can be more efficiently broken down into products like biofuels, says Rutgers plant biologist Eric Lam.

Lam, Chundawat and their colleagues took cells from the plant Arabidopsis thaliana and stripped away their walls. Because certain environmental conditions can harm cells, the team used a special microscope that minimized cells’ exposure to light, created a cooling system that kept cells at a balmy 18° Celsius and made a glowing molecular probe that stuck to fresh cellulose without interfering with wall-building. Fourteen wall-less cells were imaged every six minutes for about 24 hours as they regenerated their protective barriers. Some of the process was so speedy that additional cells were imaged at 20-second intervals for one to two hours.

The researchers identified four stages of cell wall development. First, enzymes in the cell’s outer layer pump out short pieces of cellulose that “swim around” on the cell’s surface, Lam says. Next, those fragments start to collide and attach to one another. Then, as the cellulose fibers continue to thicken and elongate, they also link up with perpendicular fibers to form a mesh. Finally, that mesh of cellulose keeps rearranging itself and compacting until it becomes a rigid, stable cell wall.

Details about these steps, particularly the first that shows cellulose isn’t produced as long strings, have remained a mystery since cell walls were first viewed through a microscope more than 300 years ago, says Rutgers biophysicist Sang-Hyuk Lee. The new study is “a big step forward in terms of understanding the fundamentals of plant biology.”