Visualization of the nanoscale pattern of recently-deposited cellulose microfibrils and matrix materials in never-dried primary walls of the onion epidermis
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For more than 10 years epidermal cell layers from onion scales have been used as a model system to study the relationship between cellulose orientation, cell growth and tissue mechanics. To bring such analyses to the nanoscale, we have developed a procedure for preparing epidermal peels of onion scales for atomic force microscopy to visualize the inner surface (closest to the plasma membrane) of the outer epidermal wall, with minimal disturbance and under conditions very close to the native state of the cell wall. The oriented, multilayer distribution of cellulose microfibrils, approximately ~3 nm wide, is readily observed over extended lengths, along with other features such as the distribution of matrix substances between and on top of microfibrils. The microfibril orientation and alignment appear more dispersed in younger scales compared with older scales, consistent with reported values for mechanical and growth anisotropy of whole epidermal sheets. These results open the door to future work to relate cell wall structure at the nm scale with larger-scale tissue properties such as growth and mechanical behaviors and the action of cell wall loosening agents to induce creep of primary cell walls.
KeywordsCellulose microfibrils Primary cell wall Atomic force microscopy Cell wall structure Matrix polysaccharides
This work was supported as part of The Center for LignoCellulose Structure and Formation, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0001090. We thank Mr. Ed Wagner for technical help as well as Dr. Seong H. Kim and Dr. Yong Bum Park for discussion and advice.
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