| ULTRASTRUCTURE OF THE NUCLEOLUS AND REPLICATION SITES OF RIBOSOMAL DNA IN Allium cepa |
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| 作者姓名： | 郝水 焦明大 邢苗 |
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| 作者单位： | Department of Biology，Northeast Normal University，Department of Biology，Northeast Normal University，Department of Biology，Northeast Normal University Changchun 130024，PRC，Changchun 130024，PRC，Changchun 130024，PRC |
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| 摘 要： | Our conventional EM observations indicate that the nucleolus of Allium cepa is composedof the fibrillar centre (FC), fibrillar component (F) and granular region (G). FC is an elec-tron-lucid zone which contains condensed or loosened chromatin. F is a circular, highly elec-tron-dense component which surrounds FC and consists of compact fibrils. EM autoradiographic(EM ARG) studies with ~3H- UdR reveal that the synthesis of ribosomal RNA (rRNA) takesplace in F. G is situated around F and composed of granules about 25 to 30 nm in diameter.EM ARG studies with ~3H- TdR demonstrate that silver grains are predominantly located in Gof the nucleolar periphery and the region of the nucleolus-associated chromatin. In addition,~3H- TdR labels are also present, but with a much lower frequency, in FC. F and G of the nu-cleolar interior. According to the distribution and sphere of silver grains in different compo-nents of the nucleolus, we suggest that the replication sites of ribosomal DNA (rDNA) aremainly located in
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ULTRASTRUCTURE OF THE NUCLEOLUS AND REPLICATION SITES OF RIBOSOMAL DNA IN Allium cepa |
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| HAO SHUI,JIAO MING-DA,XING MIAO.ULTRASTRUCTURE OF THE NUCLEOLUS AND REPLICATION SITES OF RIBOSOMAL DNA IN Allium cepa[J].Science in China(Chemistry),1991(3). |
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| Authors: | HAO SHUI JIAO MING-DA XING MIAO |
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| Institution: | HAO SHUI,JIAO MING-DA,XING MIAO Department of Biology,Northeast Normal University,Changchun 130024,PRC |
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| Abstract: | Our conventional EM observations indicate that the nucleolus of Allium cepa is composed
of the fibrillar centre (FC), fibrillar component (F) and granular region (G). FC is an elec-
tron-lucid zone which contains condensed or loosened chromatin. F is a circular, highly elec-
tron-dense component which surrounds FC and consists of compact fibrils. EM autoradiographic
(EM ARG) studies with ~3H- UdR reveal that the synthesis of ribosomal RNA (rRNA) takes
place in F. G is situated around F and composed of granules about 25 to 30 nm in diameter.
EM ARG studies with ~3H- TdR demonstrate that silver grains are predominantly located in G
of the nucleolar periphery and the region of the nucleolus-associated chromatin. In addition,
~3H- TdR labels are also present, but with a much lower frequency, in FC. F and G of the nu-
cleolar interior. According to the distribution and sphere of silver grains in different compo-
nents of the nucleolus, we suggest that the replication sites of ribosomal DNA (rDNA) are
mainly located in G of the nucleolar periphery and the region of the nucleolus-associated chro-
matin. Our observations also suggest that some segments of rDNA initiate their replication in
FC and then move to the nucleolar periphery. |
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| Keywords: | nucleolus replication sites rDNA Allium cepa |
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