Xylan deposition on secondary wall of Fagus crenata fiber |
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Authors: | T Awano K Takabe M Fujita |
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Institution: | (1) Laboratory of Plant Cell Structure, Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kyoto, JP |
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Abstract: | Summary. Delignified and/or xylanase-treated secondary walls of Fagus crenata fibers were examined by field emission scanning electron
microscopy. Microfibrils with a smooth surface were visible in the innermost surface of the differentiating fiber secondary
wall. There was no ultrastructural difference between control and delignified sections, indicating that lignin deposition
had not started in the innermost surface of the cell wall. There was no ultrastructural difference between control and xylanase-treated
sections. Microfibrils on the outer part of the differentiating secondary wall surface had globular substances in delignified
sections. These globular substances disappeared following xylanase treatment, indicating that these globules are xylan. The
globular substances were not visible near the inner part of the differentiating secondary wall but gradually increased toward
the outer part of the secondary wall, indicating that xylan penetrated into the cell wall and continuously accumulated on
the microfibrils. Mature-fiber secondary walls were also examined by field emission scanning electron microscopy. Microfibrils
were not apparent in the secondary wall in control specimens. Microfibrils with many globular substances were observed in
the delignified specimens. Following xylanase treatment, the microfibrils had a smooth surface without any globules, indicating
that the globular substance is xylan. These results suggest that cellulose microfibrils synthesized on the plasma membrane
are released into the innermost surface of the secondary wall and coated with a thin layer of xylan. Successive deposition
of xylan onto the cell wall increases the microfibril diameter. The large amounts of xylan that accumulated on microfibrils
appear globular but are covered with lignin after they are deposited.
Received February 20, 2001/Accepted September 1, 2001 |
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Keywords: | : Xylanase Lignin Xylan Cellulose Secondary wall Fagus crenata |
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