Response of Lemna minor L. to short-term cobalt exposure: The effect on photosynthetic electron transport chain and induction of oxidative damage

• Cobalt (Co2+) impaired the function of oxygen evolving complex (OEC) in L. minor L.
• Electron transport through PSII components varied depending on Co2+ concentration.
• K-band was proven to be suitable parameter for investigation of Co2+ toxicity.
• Increased lipid peroxidation level showed early oxidative damage induced by Co2+.

The effect of two concentrations of cobalt (Co2+) on photosynthetic activity and antioxidative response in Lemna minor L. were assessed 24, 48 and 72 h after the start of the exposure. Higher concentration of cobalt (1 mM) induced growth inhibition while lower concentration (0.01 mM) increased photosynthetic pigments content. Analysis of chlorophyll a fluorescence transients revealed high sensitivity of photosystem II primary photochemistry to excess of Co2+ especially at the higher concentration where decreased electron transport beyond primary quinone acceptor QA− and impaired function of oxygen evolving complex (OEC) was observed. Due to impairment of OEC, oxygen production was decreased at higher Co2+ concentration. Activity of superoxide dismutase was mainly inhibited while lipid peroxidation increased, at both concentrations, indicating that cobalt-induced oxidative damage after short exposure and moreover, susceptibility of the membranes in the cell to cobalt toxicity. Results obtained in this study suggest possible application of used parameters as tools in assessment of early damage caused by metals.