Response of oxidative stress enzymes in charophyte <i>Nitellopsis obtusa</i> exposed to allochthonous leaf extracts from beech <i>Fagus sylvatica</i>

Abstract

* Corresponding author. E-mail: reda_grigutyte@yahoo.com Leaf litter is one of the allochthonous sources of dissolved organic carbon (DOC) in freshwater ecosystems. Th roughout the degradation of leaves, a lot of chemical compounds are set free into water, which may promote oxidative stress via generation of reactive oxygen species and / or by disturbance of the intracellular oxidative balance in aquatic organisms. We investigated concentrationand time-dependent relationships for the activities of oxidative stress enzymes in macrophytic algae cells of Nitellopsis obtusa, induced by beech Fagus sylvatica leaf extracts, respectively, 0.11–55.0 mg L–1 DOC (aft er 24 h) and 1.1 mg L–1 DOC aft er (15 min – 24 h). Th e oxidative stress enzymes included catalase (CAT – E. C. 1.11.1.6), glutathione reductase (GR – E. C. 1.6.4.2), cytosolic and microsomal glutathione S-transferase (GST – E. C. 2.5.1.18). A signifi cant increase in sGST and mGST activities aft er a 24-h exposure to 1.1–11.0 mg L–1 and to 5.5 mg L–1 DOC of beech leaf extracts was detected. sGST activity signifi cantly increased in the whole period of exposure, while mGST activity decreased below control levels when exposed for 1–4 h. Glutathione reductase activity increased signifi cantly at all DOC concentrations of beech leaf extracts aft er 24 h of exposure. Th e highest elevation of GR activity was observed in extracts containing 5.5 mg L–1 DOC and the lowest activity increment at 0.11 mg L–1 DOC. A statistically signifi cant increase in GR activity started aft er 1 h (at 1.1 mg L–1 DOC) and was evident until the end of the 24-h exposure. Th e activity of catalase increased signifi cantly only at the lowest (1.1 mg L–1) DOC concentration aft er 24 h of exposure. Beech leaf extracts induced a statistically signifi cant time-dependent elevation of CAT activity during the whole period of exposure. In general, an increase of antioxidative enzyme activities in charophyte Nitellopsis obtusa indicated that the defence mechanisms against oxidative stress were induced when cells had been exposed to beech leaf extracts.