PROLONGED INCUBATION WITH LOW CONCENTRATIONS OF MERCURY ALTERS ENERGY-TRANSFER AND CHLOROPHYLL (CHL) A PROTEIN COMPLEXES IN SYNECHOCOCCUS-6301 - CHANGES IN CHL A ABSORPTION AND EMISSION CHARACTERISTICS AND LOSS OF THE F695 EMISSION BAND

Synechococcus PCC 6301 cells grown in the presence of low sublethal le vels of (about 2 mu M) mercury induced alterations in chlorophyll (Chl ) a absorption without significant alterations in phycocyanin, Chl a f luorescence emission in Hg2+-raised cells showed a large (about 18 nm) blue shift in the peak emission, No major spectral changes in phycobi lisome (PBsome) emission characteristic were noticed, indicating major structural alterations in Chl-protein complexes by incubation with Hg 2+ ions. Low temperature (77 K) emission spectra of cells grown in the presence of Hg2+ showed a loss of the characteristic Chl a emission b and at 695 nm (F695), which is known to be linked to photosystem II ph otochemistry and to originate from the Chl a of core antenna polypepti de CP 47 of photosystem II. The SDS-PAGE polypeptide profile of thylak oids indicates a loss of a polypeptide(s) with a molecular mass betwee n 40 and 60 kDa by Hg2+ incubation of cells, Our results suggest that prolonged incubation of Synechococcus 6301 cells with low concentratio ns of Hg2+ affects the Chl a spectral properties and the structure of Chl-protein complexes.