緑藻カプサアオノリの生活環について

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タイトル別名
  • リョクソウ カプサアオノリ ノ セイカツカン ニ ツイテ
  • Life Cycle of Capsosiphon fulvescens (C. AGARDH) SETCHELL and GARDNER

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説明

The present paper deals with the life cycle of Capsosiphon fulvescens. The materials used in this experiment were mainly collected from Mogi near Nagasaki. The results obtained can be described as follows: 1) This alga grows on rocks and laver-nets in the upper and middle parts of the intertidal zone. The macroscopic young thalli of this species are found in the middle of November. They show luxuriant growth during February and March, afterwords gradually fall into decay and disappear before the end of April. 2) Spore formation of the thallus was seen through the growing seasons. Some vegetative cells of the mature thallus develop into zoosporangia, and some other cells into gametangia. The content of each zoosporangium is divided to 4, 8 or more zoospores, whilst each gametangium is divided to 32 or 64 gametes. 3) The zoospores are quadriflagellate and pear shaped, being 7～13 μ long 4～5 μ broad. They have one eye spot and show strong positive phototaxis. 4) Settled zoospores immediately germinate and develop into filamentous thalli (Fig. 2). After about 30 days culture, they grew up to 1～1.5 cm long, and discharged many zoospores and gametes. 5) The appearance and behavior of gametes resemble those of zoospores, but gametes are smaller in size, being 5～8 μ long 2.5～4.5 μ broad, and have two flagella. The conjugation of gametes takes place isogamously between gametes from distinct thalli. 6) The zygotes gradually increase in size without cell divisions and develop into cysts (Fig. 3). After two months culture, in some enlarged cysts, 16 or 32 zoospores are produced. These zoospores have four flagella and germinate to filamentous leafy thalli. 7) The parthenogenetic germination of gametes is also observed in the same way as that of the zygotes. 8) From the results of these observations, it may be considered that this alga is dioecious and isogamous, and has heteromorphous generations, one generation is the zoospore-and gamete-producing thallus and the other one is the zoospore-producing cyst.

天然の生育生態の観察や室内の培養実験を通してカプサアオノリの生活環を研究した. 1.本種は潮間帯の中部から上部の水位に着生する.肉眼でみられる幼体は11月中旬に現われ,生育は2,3月に最も旺盛で,その後は次第に衰え葉体は4月下旬には消失する. 2.生殖細胞は生育期のほとんど全期間にわたってみられ,その形成部は黄褐色を呈する.同一葉体に游走子と配偶子をつくるが,前者は生長の初期に後者は後期に多く形成される.3.葉体の游走子は,栄養細胞が4,8または16個に分裂してつくられ,西洋梨で,4鞭毛と1眼点を有し,大きさは径4～5μ長さ7～13でて,強い走光性を示す. 4.着生した游走子は直ちに葉状体に発育する.その発芽体は培養約30日後には1～15cmに達し,多くの游走子や配偶子を放出するようになった. 5.配偶子は栄養細肥が32,64個に分裂してつくられ,その形態や動作は游走手と似ているが,やや小型(径2.5～45μ長さ5～8μ)て2鞭毛を有する.接合現象は違った個体からの配偶子間で観察され,同型配偶のようである. 6.接合子は増大生長してcystに発育する.増大したcystには16,32個の4鞭毛の游走子がつくられ,それは葉状体に生長する. 7.接合しなかった配偶子は単為的に発生するが,その発芽体もcystとなる. 8.このような観察結果から,カプサアオノリは雌雄異株で同型配偶を行ない,葉体とcystの異型二世代をもつと考えられる.

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