浮游性コレオトリカ目繊毛虫 Strombidium conicum のchloroplast取り込み観察法とencystment誘導に関する研究

抄録

Planktonic ciliates are generally known to be strictly heterotrophic, but many marine Strombidiidea including Laboea strobila, and some Tontonia and Strombidium contain functional chloroplasts and perform photosynthesis. These mixotrophic planktonic ciliates isolate chloroplasts from their diet algae. Such behavior of the isolation and sequestration of a cell organ of different creature is interesting not only from ecological but also from evolutional point of view. The purpose of this study is to get enough number of virgin vegetative cells of a planktonic ciliate without chloroplasts to follow the processes of the isolation/sequestration of chloroplasts after supplying diet algae. One of the most dominant planktonic ciliates, Strombidium conicum, in Onagawa Bay, Japan sequesters the functional chloroplasts from ingested phytoplankton. Kim and Taniguchi (1995, 1997) isolated the cysts of this species from sediment samples collected in the bayand successfully identified outenal conditions induce excystment in laboratory. Then, it is theoretically possible to obtain enough number of the newly excysted virgin cells in laboratory if the encystement can also be artificially induced. We put some stresses on a clonal Strombidium conicum population but encystment could not be induced. However, during continual cultures of mixed clones numerous encystements occurred along with a few conjugations after 15–17 times of binary fissions. This suggests that aging and conjugation are necessary for the encystment in this species.