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Regulation of life cycle in epiphytic brown alga dictyosiphon foeniculaceus

Scientific Papers of the Institute of Algological Research Faculty of Science Hokkaido University 8(1): 31-62
Regulation of life cycle in epiphytic brown alga dictyosiphon foeniculaceus
Epiphytic marine brown alga, Dictyosiphon foeniculaceus from Muroran, Hokkaido, was investigated to clarify the entire life cycle, sexual evidence and nuclear phase in laboratory cultures. Dictyosiphon foeniculaceus showed heteromorphic alternation of generations between a macrothallus bearing unilocular sporangia and a microthallus bearing plurilocular sporangia, and the nuclear phases of all stages were haploid (n=8). The sexual process was not observed and the alternation of nuclear phases did not occur. The life cycle of this species was regulated by several environmental factors, especially a chemical substance contained in seawater and the host community. The life cycle of Dictyosiphon foeniculaceus was regulated by using PSIS (plurilocular sporangium inducing substance) and MIS (macrothallus inducing substance) in pure culture, and characterization of PSIS and MIS was attempted. According to the results obtained, the following factors were clarified. The life cycle of D. foeniculaceus was not completed under axenic ASP 12-NTA medium, only vegetative growth of microthalli was observed repeatedly. The PSIS-activity is present in seawater, yeast extract, malt extract and Neorhodomela extract, and it appeared as a strong polarized fraction of Neorhodomela extract. This indicates that PSIS may be a kind of sugar or a related substance. On the other hand, the MIS-activity was discovered in extract of the parasitic yellow bacteria on Scytosiphon thallus and it appeared in a volatile fraction, and this indicates that MIS may be a carbohydrate. By the nutritional study, PSIS is identified with inositol or its chemical analogue and MIS is regarded as an unknown substance. The entire life cycle of Dictyosiphon foeniculaceus was completed in axenic artificial medium containing PSIS and MIS for the first time.

Accession: 006288995

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