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ISSN Imprimir: 1521-9429
ISSN On-line: 1940-4328
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Cyanelles and taxonomic status of cyanomes
RESUMO
The available data on ultrastructure, physiology, biochemistry and molecular biology of cyanelles testify that they can be regarded as the ancient type of plastids, possessing common features both with free-living Cyanophyta (remains of cell wall of prokaryotic type, phycobiliprotein antenna, single localization of thylakoids with interthylakoid phycobilisomes, carboxisomes, host-independent 16S rRNA synthesis, encoding of both subunits of ribulose-bisphosphate carboxylase and ferredoxin by their own genome, ability of atmospheric nitrogen fixation in some individuals) and chloroplasts (genome reduction and host-dependent synthesis of main pigments, proteins, loss of a set of carotenoids, enzymes and inclusions peculiar to free-living Cyanophyta, the inability to respire independently etc.). Based on analysis of these features in a set of cyanomes with various degree of integration with their partners, the main directions of the endosymbionts' evolution towards their conversion into cyanelle (cyanoplast) and chloroplast were outlined. The results of studies on cyanelles obtained at the molecular level testify that chloroplasts have an endosymbiogenic origin. The taxonomic position of cyanomes remains uncertain. Creation of the natural division Glaucophyta Skuja, 1954 or Glaucocystophyta Kies et Kremer, 1986 is not a final solution of the issue, because a set of cyanomes remains beyond it. The problem of elaboration of the principles of classification of organisms with dual nature arises.