THE ROLE OF REACTIVE OXYGEN SPECIES IN COPPER TOXICITY TO TWO FRESHWATER GREEN ALGAE¹

Abstract

The role of reactive oxygen species (ROS) in copper (Cu) toxicity to two freshwater green algal species, Pseudokirchneriella subcapitata (Korshikov) Hindák and Chlorella vulgaris Beij., was assessed to gain a better mechanistic understanding of this toxicity. Cu-induced formation of ROS was investigated in the two algal species and linked to short-term effects on photosynthetic activity and to long-term effects on cell growth. A light- and time-dependent increase in ROS concentrations was observed upon exposure to environmentally relevant Cu concentrations of 50 and 250 nM and was comparable in both algal species. However, effects of 250 nM Cu on photosynthesis were different, leading to a 12% reduction in photosynthetic activity in P. subcapitata, but not in C. vulgaris. These results indicate that differences in species-specific sensitivities measured as photosynthetic activity were not caused by differences in the cellular ROS content of the algae, but probably by different species-specific ROS defense systems. To investigate the role of ROS in Cu-mediated inhibition of photosynthesis, the ROS scavenger N-tert-butyl-α-phenylnitrone (BPN) was used, resulting in a reduction of Cu-induced ROS production up to control level and a complete restoration of photosynthetic activity of Cu-exposed P. subcapitata. This finding implied that ROS play a primary role in Cu toxicity to algae. Furthermore, we observed a time-dependent ROS release process across the plasma membrane. More than 90% of total ROS were determined to be extracellular in P. subcapitata, indicating an efficient method of cellular protection against oxidative stress.

Evaluation of Copper Oxide Nanoparticles Toxicity Using Chlorophyll a Fluorescence Imaging in Lemna gibba

“…Cu 2+ was also found to increase the sensitivity of leaves to photoinhibition by light and oxidative stress due to its competition with iron as an essential element [39]. Oxidative stress was also found to have a major role in Cu 2+ toxicity in photosynthetic organisms [40]. For CuO NPs, a strong production of reactive oxygen species was observed in algal cells exposed under light conditions to CuO NPs concentrations of 0.02 g/L [11].…”

“…Aquatic photosynthetic organisms represent the main source of biomass in the aquatic trophic chain and these organisms are very sensitive to the effects of copper species. It has been reported that copper may induce strong inhibition of photosynthetic electron transport mboxprocesses and oxidative stress at cellular level [12,13]. We reported recently that CuO NPs, having a core of CuO NPs and a shell of polyacrylic acid (PAA), were found to be very toxic to unicellular algae, causing inhibition of PSII electron transport capacity in Chlamydomonas reinhardtii cultures [11].…”

Impact of nano titanium dioxide exposure on cellular structure of Anabaena variabilis and evidence of internalization

“…Reactive oxygen species production: oxidative stress Total ROS formation were determined according to the method described by Knuaert et al [20] using the fluorogenic permeable probe 2 0 ,7 0 -dichlorodihydrofluorescein diacetate (H 2 DCFDA; Invitrogen). The probe is first hydrolyzed to the nonfluorescent dichlorodihydrofluorescein (H 2 DCF) by cellular esterase before being transformed to the highly fluorescent dichlorofluorescein (DCF) in the presence of ROS and cellular peroxidases.…”

Generation of reactive oxygen species in cyanobacteria and green algae induced by allelochemicals of submerged macrophytes

“…The stock solution of DCFH-DA was prepared in DMSO at a concentration of 10 mM and stored at À20°C. The ROS level was determined as the method described by Schrader et al (2005) and Knauert and Knauer (2008).…”