Structural inhomogeneity of cellulose assembly in plant cell wall affecting anisotropic mechanical property


Cellulose microfibrils (CMFs) in plant cell walls are a major load-bearing component, and the microfibril structure is a key factor that regulates plant cell wall mechanics that is critical to the wall extension and cell growth. Thus, the structure of CMFs in plant epidermal cell walls has been widely studied for the microfibril structure-wall mechanic relationship because of its ease of access for characterization and mechanical tests. However, the structural information of CMFs has been deduced from the assumption that the whole tissue has a uniform CMF structure. Here, we report the distinct CMF assemblies in the epidermal cell edges compared to that in the cell faces. The vibrational sum frequency spectroscopy (SFG) imaging found that the CMFs in the cell edges are preferentially aligned perpendicular to the anticlinal wall plane, while the CMFs in the cell faces have the known crossed-polylamellate structure. This discovery clarifies the discrepancies in CMF structural information obtained with different techniques. Also, it suggests that the origin of the anisotropic mechanical properties of single epidermal cell wall tissues is due to the cell edges where CMFs are preferentially aligned.

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