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Melosira moniliformisの有性生殖

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Title: Melosira moniliformisの有性生殖
Other Titles: Sexual Reproduction of Melosira moniliformis AGARDH
Authors: 右田, 清治
Authors (alternative): Migita, Seiji
Issue Date: Aug-1967
Publisher: 長崎大学水産学部
Citation: 長崎大学水産学部研究報告, v.23, pp.123-133; 1967
Abstract: The auxospores of centric diatoms had long been thought to be formed asexually. In recent years, our knowledge of the sexual reproduction and life history of the diatoms has been greatly advanced. Accordingly, STOSCH1) demonstrated auxospore formation by oogamy in Melosira varians, and then STOSCH2-5) and DREBES6・7) studied sexual reproduction in several species of Centrales. In the present report, the author studied on the morphology and ecology of sexual reproduction of Melosira moniliformis AGARDH, using materials collected from the mouth area of the Hachiro River near Nagasaki. Some physical factors affectinggametogenesis of this alga, such as temperature, light intensity and chlorinity, were also studied experimentally. The results obtained are summarized as follows: The formation of spermatogonia and oogonia was observed on narrow clones, ranging between 7μ and 20μ in diameter. The male cell, after one or two mitotic cell divisions, forms two or four spermatogonia, and then produces four spermatozoa in each spermatogonium. The spermatozoa are globular or ovate in shape, being 10~12μ long and 5~8μ wide, poor in plastids, and they each possess one flagellum of about 18μ. The spermatozoa leave behind much of the cystoplasm and the plastids at the time of swimming. The oogonia are developed directly from vegetative cells, accompanied by elongation of the cell and multiplication of plastids. One egg cell is formed in each oogonium. After fertilization, a zygote develops into an auxospore. Fully grown auxospores are enlarged 2.3 times the mother cells in mean diameter. This alga is monoecious, one clone producing male and female gametes, like all centric diatoms hitherto studied. The sexuality seems to be intimately connected with the phenomenon of cell size decrease in this species. The suitable size for producing male and female cells is shown in Fig. 4. In reference to physical factors affecting sexual reproduction, temperature levels between 15° and 20℃ were proved to be most effective. Especially, light intensity influenced on sex determination; female cells were mostly produced under strong light, whilst male cells were produced under weak light. / 付着性中心珪藻Meloszra monzlzformzsを分離培養し,有性細胞の形態や有性生殖の生態について研究した. 1.造精器および生卵器は7~20μの細い群体上につくられた。 2.造精器は,栄養細胞が1,2回の体細胞分裂により2または4個形成され,各造精器には4精子がつくられる. 3.精子は,径5~8μ長さ10~12μの卵形,長卵形で2,3個の小さい色素体と先端に約18μの1本の鞭毛を有し,遊泳途中に細胞質と色素体の一部を切り離す場合が多い. 4.生卵器は栄養細胞が伸長してつくられ,細胞内容も充実してくる.受精は生卵器の殼帯部内外殻のすきまより精子が進入して行なわれる. 5.受精卵は直ちに肥大して増大胞子となるが,十分に生長した増大胞子の直径は母細胞の平均2.3倍であった. 6.雌雄細胞は同一群体上につくられるので,これまでに判明した他の中心珪藻と同様に,本種は雌雄同株である. 7.本種の有性化は細胞の縮小と関係が深く,雄は7~14μ雌は9~21μの直径の細胞でそれらの形成がみられた. 8.環境条件として,温度は15,20°Cで有性細胞の形成が多かった.とくに光は性決定に影響し,生卵器は高照度(1000lux以上)でのみ形成されるのに,造精器は低照度(500lux以下)でもつくられた.
URI: http://hdl.handle.net/10069/31384
ISSN: 05471427
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:第23号

Citable URI : http://hdl.handle.net/10069/31384

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