INVESTIGATION ON THE STRUCTURE AND FUNCTION OF PYRENOIDS IN THE CHLOROPLAST OF LOWER PLANTS

形态研究组：最近的研究表明，类蛋白核是Rubisco在低等植物叶绿体中的积累部位。然而，Hori证明了一些绿藻的叶绿体DNA定位于类果核。我们研究了单细胞绿藻Trebouia的整个生命周期中叶绿体DNA和类果核的行为。当叶绿体分裂时，带有叶绿体DNA的蛋白核也分裂。在宫村海棠的生活史中，叶绿体DNA总是与类果核类物质联系在一起。Ishikawa发现DNA与晶状体形状的蛋白核结合在一起，它们散布在硅藻Nitschia sigmoidae的叶绿体基质中。最近，Suess等人(1995)报道了Rubisco分子在单细胞绿藻Clamydomonas rehardtii的类果核中并不高度集中。他们的结果是Inconsis…更多与最近的研究，其中大多数Rubisco分子定位在蛋白核。因此，Nozaki重新检查了Rubisco在莱茵哈迪伊线虫细胞中的分布，并通过冷冻固定和免疫金电子显微镜发现大多数Rubisco分子位于类蛋白核中。在Euglena中，Rubisco的小亚基定位于细胞质中隔室化的嗜奥斯体(COS)中。这一结果表明，COS要么是叶绿体蛋白质合成的细胞质部位，要么是叶绿体蛋白质从内质网到叶绿体(OSafune)运输的中间隔室。Hara用电子显微镜和分子系统发育技术重新评价了紫球藻中单细胞红藻的超微结构。这项研究表明，尽管属于这个类群的藻类在外观上相似，但它并不是一个单一的类群。生理研究组：Rubisco是类蛋白核的主要成分，如上所述，在一些藻类中也存在DNA。然而，在类蛋白核中也有可能存在其他次要成分。因此，冈田发展了新的生化技术，以鉴定类蛋白核的次要成分。在不久的将来，将使用这项技术来识别类蛋白核的次要成分。当胞外CO_2浓度从5%降至正常空气水平时，类蛋白核体积增大1.4-1.6倍，蛋白质浓度也增加(Tsuzuki)。然而，在较低的CO_2浓度下，Rubisco基因小亚基的转录本数量减少。这些结果表明，当类蛋白核在较低的CO2浓度下形成时，Rubisco是在类蛋白核中积累的，而不是新分子的合成。众所周知，在大多数藻类中，类蛋白核是由类囊体膜穿过的。Nakayama证明，光系统II存在于类蛋白核的类囊体膜中。较少

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 … More 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