At maturity, spermatozoids of the green alga Chara vulgaris are biflagellated, contain little cytoplasm, and coil for approximately 2 1/4 gyres within the mother cell wall. The anterior of the cell contains an ovoid headpiece anchoring two slightly staggered basal bodies that are positioned above and directly in front of approximately 30 linearly arranged mitochondria. An elongated stellate pattern occupies the transition zone between the BBs and axonemes. Flagella emerge from the cell just in front of the nucleus and encircle the full length of the spermatozoid. The spline comprises a maximum of 38 microtubules surrounding the anterior mitochondria and gradually decreases posteriorly to a minimum of 11. The dense nucleus is narrow, cylindrical, and occupies the central revolution of the cell. Six starch-laden plastids and associated mitochondria are linearly arranged at the cell posterior. Phylogenetic analyses of charalean taxa and archegoniates based on spermatogenesis strongly support the order Charales, with Nitella as the sister group to Chara. Diagnostic features of Chara spermatozoids include absence of a lamellar strip and axonemes embedded in the cell for almost the entire length of the anterior mitochondria. Potential relationships among Charales, Coleochaetales and archegoniates are evaluated in regards to the probable course of evolution of streamlined biflagellated gametes.

Made available in DSpace on 2017-07-10T18:13:28Z (GMT). No. of bitstreams: 1 Thamis Meurer.pdf: 1244068 bytes, checksum: 7fedbdd5b53b39bf3ab6cb34f4fac17a (MD5) Previous issue date: 2011-04-28 / The family Characeae, represented in Brazil by the genera Chara and Nitella, is considered the closest living relatives of terrestrial plants and play several ecological roles, such as the increase of water transparency and habitat complexity. This research aimed to verify the composition and structure of Characeae community at Itaipu reservoir (24°05´S e 25°33´S; 54°00´W e 54°37´W), formed in Parana river, relating them to simple environmental variables, such as conductivity, water transparency and fetch. Samples were collected in eight arms of rivers that form the Brazilian side of the reservoir (Arroio Guaçu, São Francisco Verdadeiro, São Francisco Falso, São Vicente, São João, Ocoí, Pinto e Passo Cuê). A total of 17 taxa were identified, of which Chara hydropitys Reichenbach, C. rusbyana Howe, Nitella axillaris A. Braun, N. glaziovii G. Zeller, N. gracilis (Smith) C. Agardh, N. hyalina (DC) C. Agardh, N. inversa Imahori and N. microcarpa Braun, represent new citations in the Itaipu Reservoir and Paraná State. Chara guairensis, Nitella furcata and Nitella glaziovii showed the largest geographical ranges, while Chara hidropytis and Chara rusbyana showed more restricted distribution. Furthermore, it was found that among the environmental factors considered important for the establishing of charophytes at the tributaries of the reservoir, the underwater radiation positively affects the occurrence of the genera Chara and Nitella, while fetch values showed negative influence on the occurrence of genus Nitella during the period analyzed. / A família Characeae, representada no Brasil pelos gêneros Chara e Nitella, é considerada a ancestral mais próxima das plantas terrestres e possui uma série de papéis ecológicos, entre eles o aumento da transparência da água, aumento da complexidade de habitat. O presente trabalho objetivou verificar a composição e estrutura da comunidade de Characeae no reservatório de Itaipu (24°05´S e 25°33´S; 54°00´W e 54°37´W), formado no rio Paraná, relacionando-as com variáveis ambientais simples, tais como: condutividade, transparência da água e fetch. As coletas foram realizadas em oito braços de rios que formam a margem brasileira do reservatório (Arroio Guaçu, São Francisco Verdadeiro, São Francisco Falso, São Vicente, São João, Ocoí, Pinto e Passo Cuê). Foram identificados 17 táxons, dos quais Chara hydropitys Reichenbach, C. rusbyana Howe, Nitella axillaris A. Braun, N. glaziovii G. Zeller, N. gracilis (Smith) C. Agardh, N. hyalina (DC) C. Agardh, N. inversa Imahori e N. microcarpa Braun, todas novas citações no reservatório de Itaipu e Estado do Paraná. Chara guairensis, Nitella furcata e Nitella glaziovii apresentaram as maiores abrangências geográficas, enquanto Chara hidropytis e Chara rusbyana apresentaram distribuição mais restrita. Além disso, verificou-se que entre os fatores ambientais considerados importantes para o estabelecimento dos carófitos nos afluentes do reservatório, foi encontrado que a radiação subaquática afeta positivamente a ocorrência dos gêneros Chara e Nitella, enquanto valores de fetch demonstraram influência negativa sobre a ocorrência do gênero Nitella durante o período analisado.