Incorporation of (14)C in the cyanobacterium Synechococcus PCC 6301 following salt stress

Synechococcus PCC 6301 synthesized sucrose as a compatible solute following hyperosmotic shock induced by NaCl. Initial rates of photosynthetic (14)C incorporation were reduced following salt shock. Photosynthetic rates were comparable in cells enriched for glycogen (by growth in NO 3 (-) -deficient medium) and cells grown in NO 3 (-) -sufficient medium in the absence of osmotic shock. Incorporation of (14)C was predominantly into the NaOH fraction and the residual acidic fraction in cells grown in NO 3 (-) -sufficient medium, whereas incorporation was predominantly into the residual acidic fraction in cells grown in NO 3 (-) -deficient medium. Following salt stress, (14)C incorporation was initially into the ethanol-soluble fraction and the majority of tracer was recovered in sucrose. Carbon-14 was detected in sucrose in cells which had been enriched for [(14)C]glycogen prior to salt stress, inferring that glycogen can act as a carbon source for sucrose synthesis following salt stress. Changes in the specific activity of sucrose are consistent with an initial synthesis of sucrose from glycogen followed by synthesis of sucrose using newly fixed carbon, in response to salt stress.