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摘要
Five branched heterocystous cyanobacteria (Scytonematopsis sp., Scytonema sp., Tolypothrix ceylonica, Mastigocladus sp. and Fischerella sp.) were examined for their pattern of induction of nitrogenase activity and nif gene organization. All the forms showed the onset of nitrogenase activity after 12 h which could be correlated with the appearance of proheterocysts. The highest activity was exhibited by T. ceylonica. Hybridization studies revealed the presence of the nifD gene but the absence of the xisA gene in Mastigocladus sp. and Scytonematopsis sp. Interestingly, Tolypothrix sp, and Scytonema sp. DNA samples hybridized with xisA. Hence no uniformity seems to exist regarding the presence of xisA and the related nif gene organization in branched heterocystous cyanobacteria. This investigation throws light on the primitive character and phylogenetic relatedness of branched forms to the coccoid/colonial forms. It also provides evidence for the proposition that stigonematacean cyanobacteria may not represent the most advanced cyanobacterial forms; rather they may link the coccoid and filamentous forms.
- 出版日期1995
