According to new research that models the cell wall, the unique ability of a plant cell wall to expand without weakening or breaking – a quality required for plant growth – is due to the movement of its cellulosic skeleton. The new model, created by researchers at Penn State, reveals that cellulose chains cluster together in the cell wall, providing strength, and slide against each other when the cell is stretched, providing extensibility.
The new study, which appears online May 14 in the journal Science, presents a new concept of plant cell wall, provides insight into plant cell growth and could provide inspiration for the design of polymeric materials with new properties.
“For a long time, the dominant concept of plant cell wall has been that of a gel reinforced with cellulose fibers, the rigid cellulose rods acting as steel rebars in cement,” said Daniel Cosgrove, professor. of biology at Penn State and lead author of the article. “However, we determined that the cellulose chains stick together to form a network of cellulose bundles, which provides much higher mechanical strength than disconnected rods floating in a gel. expanding walls, sliding next to each other like an extension ladder when the cell is stretched. “
Previous approaches to modeling plant cell walls were focused either on a scale too large to incorporate the behavior of individual cell components, or on a scale too small – at the atomic level – to incorporate the actual mechanics of the cell wall. In this study, the researchers used a coarse-grained computer model of the polymers that make up the cell wall – chains of cellulose and other sugar molecules that are linked together in long chains. Instead of modeling individual atoms, the researchers represented cellulose microfibers and other components with strings of beads that behave like sticky springs, in order to mimic the physical properties of these components.
“Unlike many other models, we also took into account the tendency of molecules to stick together by modeling the non-covalent bond between them,” Cosgrove said. “This allowed us to study the consequence of the interactions between the chains.”
The team specifically modeled layers of an onion cell wall so that they could compare their modeled values of mechanical characteristics to experiments conducted with real onion skins. By stretching the cell walls of the onion in several ways and using the molecular knowledge of the model, they explored the structures responsible for the unique mechanical characteristics of the cell wall.
“The walls of plant cells are unique because they have to be very strong to help protect and support the plant and very extensible because they have to expand as the plant grows,” said Yao Zhang, postdoctoral researcher in biology at Penn State and premier author of the article. “We have found that cellulose microfibers withstand most of the stress and are essential for the cell wall to maintain both strength and stretchability.”
The researchers determined that the individual cellulose fibers lined up and stuck together, forming a network of bundles. The microfibers in a bundle straighten up and can slide over each other, in a type of telescoping action, as the cell is stretched, transmitting forces between them and causing the cell to expand.
“For a long time, researchers have measured the mechanical properties, like stress and strain, of plant cell walls and how these properties change in drought and other conditions,” Cosgrove said. “But until now, we have lacked a molecular description of what is happening at the molecular level to understand these measurements. In this study, we have clarified the roles of different components in the plant cell wall and provided a quantitative framework for it. ‘interpretation of experiments used in plant research. “
The teachings from this study may be particularly useful in future work on how plants regulate their cell wall properties, which influences the rate and direction of their growth. For example, young stems quickly elongate in the spring while many fruits grow in a spherical fashion.
The researchers hope to expand their model to simulate the cell walls of other plant species and expand it to encompass an entire cell.
“Our technology currently cannot match a factory’s ability to create such a strong and stretchable material,” Yao said. “The design of plant cell walls can be an inspiration for the design of green materials with a variety of applications.”
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Material provided by Penn State. Original written by Gail McCormick. Note: Content can be changed for style and length.