EXPOSURE OF THE CYANOBACTERIUM SYNECHOCYSTIS PCC6803 TO SALT STRESS INDUCES CONCERTED CHANGES IN RESPIRATION AND PHOTOSYNTHESIS

In order to survive and to grow in the presence of a high salinity (55 0 mM NaCl) Synechocystis PCC6803 increases its energetic capacity. The salt-induced increase of electron transport rates involves both cytoc hrome c oxidase and photosystem I. In contrast, electron transport rat es measured through complexes I plus III of the respiratory chain, or through the photosystem II plus cytochrome b(6)f complexes of the phot osynthetic chain, do not show appreciable changes. The time at which c hanges in electron transport rates occur in the photosystem I and cyto chrome c oxidase complexes after the onset of salt stress indicates si milarities in the adaptation of dark respiration and (cyclic) photosyn thetic electron flow. Given an increase of whole cell respiration and of PSI cyclic electron flow larger than the neosynthesis of cytochrome aa3 and PSI reaction centers would predict, it appears that both adap tations require more than just synthesis of these two complexes.