TsHSP70 and 100 genes were significantly upregulated; ROS production and photosynthetic efficiency were adverse affectedwhen the T. suecica expose to HMsespecially the metals conjugated with SO42- anion. Overall,expression levels of both genes were much higher in SO42-conjugatedmetals than Cl- linked forms, showing that the TsHSP gene expression should be affected by metal and its conjugatedanion. This kind of transcription expression pattern was found in the dinoflagellateP.
minimum (Guo et al. 2012b), in the marine diatom Ditylum brightwellii (Guo et al. 2013) and a coral Montastraea franksi under exposure to redox-activemetal pollutants copper (Venn et al. 2009).
In addition, in the marine diatom Ditylum brightwellii when they exposure metals conjugate withSO4 and Cl2, the metals join with SO4 anionshowed increased gene expression when compared to Cl2 basedchemicals (Guo et al. 2013). Moreover, similar results were found in microalgae P.minimum by using the stress-responsive genecatalase-peroxidase (KatG) (Guo and Ki 2013).These data suggest that HSPs aredifferentially involved in defense against various metal stressors. From theprevious findings and our result it is important point needs to be considered;it seems that anionic conjugates of metal (SO4, Cl2, etc.) may be responsible forspecific induction of HSP genes. This can be observed from the fact that metalions conjugated with SO4 were able to modulate the transcription of HSP70 and 100; however this was not the case for metals conjugated with Cl2.
In another point of view, it might be explained by consideringthe biological end points as one of the indicators for the bioavailability (orsusceptibility) of metals in phytoplankton (Campbell et al. 2002). However, thecopper used in the present study are conjugated compounds (CuSO4 andCuCl2), and potentially dissolve differentially in the filteredseawater medium. Inaddition, they could react with the chelating agents EDTA present in the f/2medium. Similar metal reaction could also explain the behavior of anotherdivalent metal viz., cadmium.
Thus,the bioavailability or susceptibility of metal salts may differently affect thetoxicity and stress gene expression in the marine green algae T. suecica (Guo et al. 2012b).
