Localization of Fe‐containing superoxide dismutase in cyanobacteria from the Baltic Sea: depth and light dependency

Abstract

The abundance and cellular location of Fe-containing superoxide dismutase (Fe-SOD) in trichomes of Nodularia, Aphanizomenon and Anabaena collected from various depths in the Baltic Sea, and in trichomes of a cultured Nodularia strain, BC Nod-9427, isolated from the Baltic Sea, was examined by immunogold labelling. For trichomes collected from natural populations the areal concentration of Fe-SOD labelling decreased with depth : trichomes collected from surface accumulations had between 8 and 11 gold particles µm −# whereas trichomes collected from a depth of 18 m were unlabelled. When trichomes collected from a depth of 10 m (mean areal labelling density 0n5 gold particles µm −# ) were exposed to the higher irradiances present at 1 m, the areal concentration of Fe-SOD increased to 3n5-4 gold particles µm −# within 4 h. When cultures of Nodularia strain BC Nod-9427, adapted to low light (10 µmol m −# s −" ), were transferred to an incident irradiance of 1350 µmol m −# s −" , a doubling of the areal concentration of Fe-SOD gold label was observed within 1 h. Addition of 3-(3,4-dichlorophenyl)-1,1h-dimethylurea (DCMU) to cultures immediately before their transfer to increased illumination resulted in a decrease in areal Fe-SOD concentrations whereas addition of CdCl # caused an increase over and above that induced by the elevated irradiance. These results suggest that Baltic Sea cyanobacteria are able to modulate their Fe-SOD content but that this might be in response to oxidative stress rather than to light per se.

Antioxidant metabolism in the intertidal red seaweed Stictosiphonia arbuscula following desiccation

“…There is considerable evidence in the literature suggesting that maintenance of existing antioxidant pools or increased scavenging capacity is important for the survival of plant cells and cyanobacteria exposed to prolonged environmental stresses, including desiccation (Sgherri et al 1994a;Smirnoff 1995;Alscher et al 1997;Canini et al 1998;Shirkey at al. 2000).…”

Investigations on cyanobacterial diversity in a shallow estuary (Southern Baltic Sea) including genes relevant to salinity resistance and iron starvation acclimation

“…The sampling period was in the summer maximum of cyanobacterial biomass with continuing high irradiance levels. Although iron can be photochemically reduced and therefore be better available for phytoplankton, simultaneously oxidative stress is accompanied by the elevated demand for iron‐containing superoxide dismutase (Canini et al ., 1998), which can further increase the general iron demand of cyanobacteria. Further investigations, such as quantification of isiA expression for the isiA genotypes are necessary to understand cyanobacterial iron demand in eutrophic waters.…”

THE ROLE AND EVOLUTION OF SUPEROXIDE DISMUTASES IN ALGAE1

“…Studies using a variety of mutants, inhibitors, and light conditions have demonstrated that FeSOD is associated with the photoprotection of PSI (Herbert et al 1992, Thomas et al 1998). Field data also illustrated the selective protective functions for the SODs, as FeSOD was largely associated with nitrogen‐fixing heterocysts that only contain PSI (Canini et al 1998). Specifically, cells exposed to higher irradiances showed a dramatic increase in SOD activity and content.…”

“…Metal stress also initiated an increase in mRNA transcript levels of sodB (which encodes FeSOD); however, the translation of these transcripts appeared to be regulated by a circadian rhythm, so that conclusive evidence for the direct regulation of FeSOD by ROS has yet to be demonstrated. Responses to high metal concentrations have also been found in diatoms and green algae (Rijstenbil et al 1994, Canini et al 1998).…”