Thiol pools and glutathione redox ratios as possible indicators of copper toxicity in the green macroalgae Enteromorpha spp. from the Scheldt Estuary(SW Netherlands, Belgium) and Thermaikos Gulf (Greece, N Aegean Sea)

Defence mechanisms against Cu toxicity were examined in two dominant Entero morpha species from two coastal water types. The macroalgae were collected at three locations in the eulittoral of the Scheldt Estuary (Netherlands, B elgium) and the Thermaikos Gulf (Greece). For 10 days E. prolifera (Scheldt ) and E. linza (Thermaikos) were incubated in seawater media of different s alinities: 6, 9, 23 psu and 25, 30, 35 psu, respectively. In one series, me dia were enriched with 100 mu g Cu l(-1); responses were compared with thos e in controls with no extra Cu added. Enteromorpha, which is frequently use d as a monitor species for heavy metal contamination, had relatively high C u tissue levels (0.5-3.8 mu mol Cu gdwt(-1)). Cu levels in E. prolifera con trols (Scheldt) decreased with salinity; this was not the case with Cu leve ls in E. linza controls (Thermaikos). During the 10-d incubation algal prot ein contents and tissue Cu were rather stable. In E. linza (Thermaikos) alg al protein contents were significantly lower than those of E, prolifera (Sc heldt), although there was no indication for nitrogen limitation in E. linz a. E. linza also had much lower glutathione pools than E. prolifera. Only u nder acute Cu stress (metal addition) did E. prolifera synthesise metal-bin ding thiols (phytochelatins). Phytochelatin pools are not suitable as an in dicator of the Cu levels in these algae. The glutathione redox ratio GSH:(G SH + 0.5GSSG) was used as an indicator of (Cu-induced) oxidative stress. In E. prolifera (Scheldt) this ratio decreased with algal Cu content (P < 0.0 5), from similar to 0.5 to similar to 0.2. The average glutathione ratios i n Enteromorpha from the Scheldt and Thermaikos showed some oxidative stress induction with increasing algal Cu contents, however more clearly if Cu wa s added. As this redox ratio can also be influenced by environmental factor s such as irradiance and desiccation, it may not be useful as an indicator for Cu-induced oxidative stress in situ.