Fluorescence microscopy reveals variations in cellular composition during formation of akinetes in the cyanobacterium Aphanizomenon ovalisporum

Akinetes are differentiated, thick-walled, resting cells produced by many species of the filamentous heterocystous cyanobacteria belonging to the Nostocales and Stigonematales. They are commonly developed after the end of exponential growth and are normally resistant to low temperatures and to desiccation for extended periods. Akinetes maintain a low level of metabolic activities such as photosynthesis, respiration and de novo synthesis of proteins and lipids. In a previous study we reported that mature akinetes of Aphanizomenon ovalisporum maintained only residual photosynthetic activity. However the cellular abundance of PSI and PSII reaction centres increased in akinetes relative to exponentially grown vegetative cells while the ratio of PSI to PSII remained relatively unchanged. In the present study we provide spectral and biochemical evidence that akinetes lose their phycobilisomes during their development. DAPI stained trichomes of exponentially grown cultures emitted fluorescence signals attributed...