Possible involvement of membrane fluidity in helicoidal microfibrillar orientation in the coenocytic green alga,Boergesenia forbesii |
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Authors: | S Mizuta A Watanabe S Kimura K Yoshida |
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Institution: | (1) Department of Biology, Faculty of Science, Kochi University, Akebono-cho, 780 Kochi, Japan |
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Abstract: | Summary Microfibrillar textures and orientation of cellulose microfibrils (MFs) in the coenocytic green alga,Boergesenia forbesii, were investigated by fluorescence and electron microscopy. Newly formed aplanosporic spherical cells inBoergesenia start to form cellulose MFs on their surfaces after 2 h of culture at 25°C. Microfibrillar orientation becomes random, fountain-shaped, and helicoidal after 2, 4, and 5 h, respectively. The fountain orientation of MFs is usually apparent prior to helicoidal MF orientation and thus may be considered to initiate helicoid formation. Microfibrils continue to take on the helicoidal arrangement during the growth ofBoergesenia thallus. The helicoidal orientation of MFs occurs through gradual counterclockwise change in MF deposition by terminal complexes (TCs) viewed from inside the cell. On the dorsal side of curving TC impressions in helicoidal texture formation on a freeze-fractured plasma membrane, the aggregation of intramembranous particles (IMPs) occurs. Membrane flow may thus possibly affect the regulation of helicoidal orientation inBoergesenia. Following treatment with 3 M amiprophos-methyl (APM) or 1 mM colchicine, cortical microtubules (MTs) completely disappear within 24 h but helicoidal textures formation is not affected. With 15 M cytochalasin B or 30 M phalloidin, however, the helicoidal orientation of MFs becomes random. Treatment with CaCl2 (10 mM) causes the helicoidal MF orientation of cells to become random, but co-treatment with N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7) (100 mM) prevents this effect, though W-7 has no effect on the helicoidal MF formation. It thus follows that MF orientation inBoergesenia possibly involves actin whose action may be regulated by calmodulin.Abbreviations APM
amiprophos-methyl
- DMSO
dimethylsulfoxide
- IMP
intramembranous particle
- MF
microfibril
- MT
microtubule
- TC
terminal complex; W-7 N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide |
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Keywords: | Boergesenia forbesii Cellulose synthesizing complex Cytoskeleton Helicoidal wall Membrane fluidity Microfibril orientation Plasma membrane |
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