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auxospore
In certain species of diatoms, auxospores are specialised cells that are produced at key stages in their cell cycle or life history. Auxospores typically play a role in growth processes, sexual reproduction or dormancy.〔Hoek, C. van den, Mann, D. G. and Jahns, H. M. (1995). ''(Algae : An introduction to phycology )'', Cambridge University Press, UK.〕
Auxospores are involved in re-establishing the normal size in diatoms because successive mitotic cell divisions leads to a decrease in cell size. This occurs because each daughter cell produced by cell division inherits one of the two valves that make up the frustule (a silica cell wall), and then grows a smaller valve within it. Consequently, each division cycle decreases the average size of diatom cells in a population. When its size becomes too small, a dividing diatom cell produces an auxospore to expand its cell size back to that which is normal for vegetative cells.〔Assmy, P., Henjes, J., Smetacek, V. and Montresor, M. (2006). (Auxospore formation by the silica-sinking, oceanic diatom ''Fragilariopsis kerguelensis'' (Bacillariophyceae). ) ''J. Phycology'' 42, 1002-1006.〕
Auxospores can also play a role in sexual reproduction in diatoms, and may be formed after haploid gametes fuse to form a diploid zygote.〔Chepurnov, V.A., Mann, D.G., Sabbe, K. and Vyverman, W. (2004). Experimental studies on sexual reproduction in diatoms. ''International Review of Cytology'' 237, 91-154.〕
Finally, auxospores can be produced by diatoms to act as dormant stages, sometimes referred to as "resting spores." These are used to survive periods of time that are unfavourable to growth, such as winter or while nutrients are depleted.〔
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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