Effects of leaf extracts on glutathione reductase expression, hydrogen peroxide and glutathione contents in the aquatic macrophyte Ceratophyllum demersum

Due to senescence and anthropogenic activities, leaves fall into aquatic systems or in their proximity. They decompose and release chemicals that may influence aquatic biota by imposing oxidative stress. It is known that allochthonous leaf litter alone contributes 30% of total dissolved organic carbon (DOC) in streams. We investigated changes in H(2)O(2) and glutathione contents in the coontail, Ceratophyllum demersum, in response to crude extracts from oak (Quercus robur) and reed (Phragmites australis). Glutathione reductase (GR) expression was assessed by semiquantitative RT-PCR. H(2)O(2) showed a dose-dependent increase that tends to plateau at high DOC concentration in both extracts. In parallel, total glutathione (GSH + GSSG) increased, whereas glutathione/glutathione disulphide (GSH/GSSG) ratio decreased. We isolated, for the first time, a partial GR sequence from C. demersum and it showed significant homology (79-85%) to GR of other plants. Transcriptional changes in GR after exposure to oak extracts occurred at high DOC concentration (10 mg/L). Reed extracts induced a downregulation of GR at 4 h. Taken together, our data provide evidence that in C. demersum, the regulation of GR expression and redox state of antioxidant (glutathione) pools are, at least in part, influenced by leaf extract-induced H(2)O(2) production. These results suggest that the mechanism of protection against stress posed by the two leaf extracts can be mediated by antioxidant redox responses and regulated GR expression. We suggest that GR could serve as an important biomarker gene in aquatic ecosystems since it was modulated at an environmentally realistic DOC concentration.