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Keywords:

  • Akinetes;
  • germination;
  • oxygenic photosynthesis;
  • carbon and nitrogen assimilation;
  • diazotrophy;
  • Anabaena

summary

The energy requirements of akinete germination in A. doliolum were met initially from aerobic oxidation of endogenously stored carbon reserve. The germination of non-photosynthetic akinetes commenced in light with new protein synthesis followed by the simultaneous development of oxygenic photosynthesis, nitrate reductase activity, glutamine synthetase activity and aspartate dehydrogenase (AsDH) activity by 24 h and heterocyst formation and nitrogenase activity by 60 h. Glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) activities were present in mature akinetes and only GPT activity increased during akinete germination. The simultaneous appearance during the course of germination of oxygenic photosynthesis, nitrate reductase activity and glutamine synthetase activity much before that of N2 fixation, implies that oxygenic photosynthesis is more closely associated developmentally with carbon dioxide and nitrate assimilation than with N2 assimilation. The activities of the transaminases (GOT and GPT) during the initial stages of germination suggest a significant role for these enzymes in amino-acid metabolism associated with germination. The appearance of nitrate reductase activity under N2-fixing conditions, in the absence of nitrate, suggests that the nitrate assimilating enzyme is not nitrate inducible.