Studies on the plastid-dividing apparatus by immuno-electron microscopy

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We were the first to identify the plastid-dividing appratus, which is located in the cytoplasm close to the outer envelope membrane at the constricted isthmus of dividing chloroplasts in the red alga Cyanidium caldarium. The project has been performed in an aim to identify the fine structures and function of plastiddividing apparatus in many plants from lower eukaryote Cyanidium caldarium RK-1 to higher plants. In lower eukaryotes, some-what electron dense body is fragmented into many, somewhat electron-dense granules as the first step and then they are alighed along the equatorial region of the chloroplast and fine filaments are formed from the somewhat electron dense granules in the equatorial region. The fine filaments have been identified as actin-like filaments by an immuno-electron microscopy. The fine filaments of the plastid-dividing apparatus align themselves according to the longest axis of their overall domain. The bundle of fine filaments begins to contract and generates a deep furrow. Since similar structures as observed extensively in the plastids of algae, moss, fern and higher plants including cultured cells, the plastid-dividing apparatus appears to be an essential structure for the division of plastids in plants. The method for isolation of plastids from the protoplasts of the tabacco cultured cells has been developed using various centrifugations and biochemical techniques. However, it was difficult to isolate clearly the plastid-dividing apparatus from the dividing plastids.