ULTRASTRUCTURAL-CHANGES INDUCED BY SELECTED CADMIUM CONCENTRATIONS INTHE CYANOBACTERIUM NOSTOC UAM208

The effects of cadmium on the fine structure of the nitrogen-fixing cy anobacterium Nostoc UAM208 have been studied. Cells were treated with final free ion Cd2+ concentrations of 4.89 and 6.36 mu M. Possible cel l damage was examined at 6, 24, 48 and 96 h of heavy metal exposure. T he main alterations induced by cadmium included the development of lar ge areas of intrathylakoidal spaces, thylakoid disorganization and deg radation, increase in the number and size of polyphosphate bodies, app earance of large cyanophycin granules and, eventually, cell lysis, lea ving a much larger proportion of heterocysts. Finally, the physiologic al relevance of these observations is discussed.