The effect of mercury on glutathione S-transferase activity in the marine phanerogam Posidonia oceanica

Shoots of Posidonia oceanica were collected in the northwestern Mediterrane an Sea, in a clean area: Villefranche-sur-mer, France, and in an area known for its mercury contamination: Rosignano, northwestern Italy. Foliar shoot s of this phanerogam collected at Villefranche-sur-mer were treated for 48 h with different mercury concentrations (0; 0.01; 0.1 and 1 mu g Hg L-1). P hotosynthetic parts (adult and intermediate blades) showed a higher capacit y for mercury uptake than that found in the sheaths. Glutathione S-transfer ase (GST) activities in foliar tissues of Posidonia oceanica from Rosignano were always higher than those from Villefranche-sur-mer. The mercury uptak e experiment tin vivo experiment) also showed an increase in GST activity a s a function of mercury concentrations. This increase was higher in the pho tosynthetic parts. The GST activity was then measured in an in vitro experi ment where different foliar tissues from both sampling sites were put in co ntact with mercury. A significant decrease in GST activity was observed as a function of mercury concentrations whatever the foliar tissue or the samp ling site considered. This phenomenon allowed the determination of the IC50 for mercury. The CST activities measured in Posidonia oceanica from the Ro signano area were more sensitive to mercury than samples from Villefranche- sur-mer. Foliar tissues also showed a different sensitivity to mercury; pho tosynthetic parts from Rosignano being more sensitive than basal parts. The kinetic parameters of GSTs were also determined in the sheaths of Posidoni a oceanica from both sites. The results of the in vitro experiment seem to indicate that the isoenzyme composition of the GSTs may vary from one site or from one foliar tissue to another. The in vivo and in vitro effects of m ercury appeared to be opposite. When Posidonia oceanica was exposed to merc ury in the field or in vivo in the laboratory, both induction and inhibitio n of GST activities may have existed. Nevertheless, induction seemed to be the predominant process. Mercury may be involved in GST enzyme induction in this marine phanerogam and in the differences observed in GST activities i n the field.