This preprint is under consideration at Cellulose. A preprint is a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
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Research Article
Junji Sugiyama
Kyoto University Graduate School of Agriculture Faculty of Agriculture: Kyoto Daigaku Nogaku Kenkyuka Nogakubu
Corresponding Author
ORCiD: https://orcid.org/0000-0002-5388-4925
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Tensile tests of birch cork were performed in the tangential direction. Birch cork in the wet state showed significantly higher extensibility and toughness than those in the oven-dried state. The histochemical structure of birch cork was investigated by microscopic observation and spectroscopic analysis. Birch cork cell walls showed a three-layered structure. In transmission electron micrographs, osmium tetroxide stained the outer and inner layers, whereas potassium permanganate stained the middle and inner layers. After chemical treatment to remove suberin and lignin, the outer and inner layers disappeared and Fourier-transformed infrared spectra showed the cellulose I pattern. Polarizing light micrographs indicated that molecular chains in the outer and inner layers were oriented perpendicular to suberin lamination, whereas those in the inner layer showed longitudinal orientation. These results suggested that the outer and inner layers mainly consist of suberin, whereas the middle layer and compound middle lamella consist of lignin, cellulose, and other polysaccharides. We hypothesized a hierarchical model of the birch cork cell wall. The lignified cell wall with helical arrangement of cellulose microfibrils is sandwiched between two suberized walls. Cellulose microfibrils in the middle layer act like a spring and bear tensile loads. In the wet state, water and cellulose in the compound middle lamella transfer tensile stress between cells. In the dried state, this stress-transferal system functions poorly and fewer cells bear stress. Suberin in the outer and inner layers prevents absolute drying to maintain mechanical properties of the bark and to bear tensile stress caused by trunk diameter growth.
Keywords
Cellulose, Cork, Polarizing light microscopy, Suberin, Transmission electron microscopy
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This preprint is under consideration at Cellulose. A preprint is a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Research Article
Junji Sugiyama
Kyoto University Graduate School of Agriculture Faculty of Agriculture: Kyoto Daigaku Nogaku Kenkyuka Nogakubu
Corresponding Author
ORCiD: https://orcid.org/0000-0002-5388-4925
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Under Review
Version 1
Posted 23 Mar, 2021
No community comments so far
Review #? received
Received 18 Mar, 2021
Reviewers invited
Invitations sent on 17 Mar, 2021
First submitted
On 13 Mar, 2021
Subject Areas
Materials Engineering
License:
This work is licensed under a CC BY 4.0 License. Read Full License
Tensile tests of birch cork were performed in the tangential direction. Birch cork in the wet state showed significantly higher extensibility and toughness than those in the oven-dried state. The histochemical structure of birch cork was investigated by microscopic observation and spectroscopic analysis. Birch cork cell walls showed a three-layered structure. In transmission electron micrographs, osmium tetroxide stained the outer and inner layers, whereas potassium permanganate stained the middle and inner layers. After chemical treatment to remove suberin and lignin, the outer and inner layers disappeared and Fourier-transformed infrared spectra showed the cellulose I pattern. Polarizing light micrographs indicated that molecular chains in the outer and inner layers were oriented perpendicular to suberin lamination, whereas those in the inner layer showed longitudinal orientation. These results suggested that the outer and inner layers mainly consist of suberin, whereas the middle layer and compound middle lamella consist of lignin, cellulose, and other polysaccharides. We hypothesized a hierarchical model of the birch cork cell wall. The lignified cell wall with helical arrangement of cellulose microfibrils is sandwiched between two suberized walls. Cellulose microfibrils in the middle layer act like a spring and bear tensile loads. In the wet state, water and cellulose in the compound middle lamella transfer tensile stress between cells. In the dried state, this stress-transferal system functions poorly and fewer cells bear stress. Suberin in the outer and inner layers prevents absolute drying to maintain mechanical properties of the bark and to bear tensile stress caused by trunk diameter growth.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
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