PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Respiration by light and KatG activity in Synechocystis PCC 6803 and Synechococcus PCC 6301 grown at high salinity. Ioan ARDELEAN^*,1, Gūnter PESCHEK², ¹ Institute of Biology, Centre of Microbiology, Bucharest, ROMANIA² Molecular Bioenergetics Group, Viena, AUSTRIA

ABSTRACT- The strategy used by cyanobacteria to cope with the presence of high salt concentrations in their environment is based on the increase in energy input (increased respiration and photosystem 1 activity ), needed for both the exclusion of salts (via antiporters) and for the accumulation (de novo synthesis or active transport) of osmotic compatible organic solutes. Here we focus on the respiration in light and on catalase-peroxidase (KatG) activity as they could be essential for cell response against high salinity. The main conclusions are: 1) Respiration in light is higher in salt adapted cells than in control cells; 2) Respiration in light (% from dark respiration) is lower in strains where the predominant localization of cytochrome c oxidase is at intracellular(= thylakoidal) membranes (e.g. in Synechocystis PCC 6803) compared to strains housing the major level of cytochrome c oxidase activity at the cytoplasmic (=plasma) membrane (e.g. in Synechococcus PCC 6301, Anabaena PCC 7120, Spirullina PCC 6313). The exception would be, of course, Gloeobacter violaceaus 3 ) the cellular localization of cytochrome c oxidase is a major factor controlling the inhibition of respiration by light in cyanobacteria, but not the only one; 4) in agreement with the biological role of KatG this enzyme has a higher rate and a higher (apparent) specificity constant ( K2/ Km ) in salt adapted cells, probably in order to better eliminate the increased hydrogen peroxide generated by increased respiratory and PS1 activities and 5) catalase and peroxidase activities of KatG have different sensitivities against NaCl both in vivo (intact cells) and in vitro (crude extracts or purified enzyme).

KEY WORDS: respiration in light, Cyanobacteria, KatG, high salinity