Salt-induced sucrose accumulation is mediated by sucrose-phosphate-synthase in cyanobacteria

In cyanobacteria sucrose-phosphate-synthase (SPS) represents the main sucrose-synthesizing enzyme, which is involved in sucrose accumulation of salt-stressed cells. The enzyme was found to be dependent on UDP-glucose. In Synechococcus sp. PCC 6301, SPS activity was stimulated by adding NaCl to the assay buffers, while in Anabaena sp. PCC 7120 enhanced NaCl concentrations in vitro did not change the SPS activity. In salt-adapted cells of these two cyanobacterial strains, osmotically significant amounts of sucrose were accumulated and the SPS activity was clearly increased compared to cells grown in basal medium. In salt-loaded cells of Synechocystis sp. PCC 6803 small amounts of sucrose were found beside the main osmolyte glucosylglycerol. A putative sps gene homolog found in the genome of Synechocystis sp. PCC 6803 was mutated by insertion of an antibiotic resistance gene cartridge. This mutation led to a complete absence of sucrose biosynthesis and SPS activity confirming the proposed function of the gene.