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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 dont know how its synthesized.Scientists want to understand how cellulose is made not only because its 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.Fibers of cellulose (illustrated in brown), which clumped together after short pieces were pumped out by plant cell enzymes (green), overlap to form a mesh over a round cell before morphing into a rigid, typically rectangular, cell wall. Ehsan Faridi/Inmywork Studio/Chundawat, Lee and Lam LabsLam, 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.Fourteen cells from the Arabidopsis thaliana plant were imaged every six minutes for about 24 hours as they regenerated their cell walls. The glow shows cellulose, chains of sugar molecules, which is the cell walls primary component.The researchers identified four stages of cell wall development. First, enzymes in the cells outer layer pump out short pieces of cellulose that swim around on the cells 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 isnt 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.
