| Co-Investigator(Kenkyū-buntansha) |
NOZAKI Hisayoshi GRADUATE SCHOOL OF SCIENCE,UNIVERSITY OF TOKYO,ASSOCIATE PROFESSOR, 大学院・理学系研究科, 助教授 (40250104)
OKADA Mitsumasa FACULTY OF SCIENCE,TOHO UNIVERSITY,PROFESSOR, 理学部, 教授 (80057629)
TSUZUKI Mikio SCHOOL OF LIFE SCIENCE,TOKYO UNIV.OF PHARMACY AND LIFE SCIENCE,PROFESSOR, 生命科学部, 教授 (70155430)
OSAFUNE Tetsuaki DEPARTMENT OF LIFE SCIENCES,NIPPON SPORT SCIENCE UNIVERSITY,PROFESSOR, 健康学科, 教授 (70074630)
ISHIKAWA Ikuko FACULTY OF EDUCATION,TOKYO GAKUGEI UNIVERSITY,PROFESSOR, 教育学部, 教授 (50074638)
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| Research Abstract |
Morphological research group : Recent studies indicate that the pyrenoid is an accumulation site of Rubisco in the chloroplast of lower plants. However, Hori demonstrated the localiation of chloroplast DNA in the pyrenoid core of some green algae. We have investigated the behavior of chloroplast DNA and pyrenoids throughout the life cycle of the unicellular green alga, Trebouxia. When the chloroplast divides, the pyrenoid with chloroplast DNA also divides. The chloroplast DNAs are always associated with the pyrenoids during the life cycle of Trebouxia (Miyamura). Ishikawa found the asscoclation of DNAs with lens-shaepd pyrenoids, which are scattered throughout the chloroplast matrix of the diatom, Nitschia sigmoidea. She also found the localization of Rubisco in the pyrenoid core of N.sigmoidea Recently, Suess et al (1995) reported that Rubisco molecules are not highly concentrated in the pyrenoid core of the unicellular green alga, Chlamydomonas reinhardtii. Their results are inconsis
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tent with recent studies in which most of Rubisco molecules are localized in the pyrenoid core. Thus, Nozaki re-examined the distribution of Rubisco in the cells of C.reinhardtii, and found the localization of most of Rubisco molecules in the pyrenoid core using cryo-fixation and immunogold electron microscopy. In Euglena, small subunit of Rubisco is found to be localized in the compartment alized osmiophilic body (COS) in the cytoplasm. This results suggests that the COS is either the cytoplasmic site of chloroplast protein synthesis or an intermediate compartment in the transport of chloroplast proteins from the ER to the chloroplast (Osafune). Hara re-evaluated the ultrastructure of the pyrenoid as the taxonomic character of unicellullar red algae in Porphyridiales using electron microscopy and molecular phylogenetic techniques. This study suggests that Porphyridiales is not a monophyletic group, although the algae belonging to this group is similar in appearance.
Physiological research group : Rubisco is the major component of the pyrenoid, and in some algae DNA is also present, as described above. However, it is possible that other minor components are present in the pyrenoid core. Therefore, Okada developed the new biochemical techniques in order to identify the minor components of the pyrenoid. The minor components of the pyrenoid will be identified using this technique in near future. When the extracellular CO_2 concentration is lowered from 5% to ordinary air level in the cells of C.reinhardtii, the pyrenoid has become 1.4-1.6 times larger in volume, and the protein concentration has also increased (Tsuzuki). However, the amount of transcripts of small subunit of Rubisco genes decreases under lower CO_2 concentration. These results suggests that when the pyrenoid develops under lower CO_2 concentration, the Rubisco is accumulated in the pyrenoid instead of the synthesis of new molecules. It is known that the pyrenoid core is traversed by thylakoid membranes in most of algae. Nakayama showed that photosystem II is present in the thylakoid membranes in the pyrenoid. Less
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