engleski

Physiological responses of Duckweed (Lemna minor L.) to short-term cobalt exposure

In this study the influence of the broad range of cobalt (CoCl2) concentrations on duckweed photosynthetic performance and oxidative stress were investigated (5μM, 10μM, 500μM and 1mM were applied in nutrient solution, respectively). The production of H2O2, lipid peroxidation level, photosynthetic pigments content and photosystem II (PSII) efficiency by OJIP test were measured after 24 hours of exposure. Results showed that plants exposure to Co2+ caused the increase in both chlorophylls and carotenoids content at 5μM and 10μM while higher concentrations did not influence pigments content. Maximum quantum yields of PSII (Fv/Fm) decreased in challenged plants still having values beyond 0.75 indicating fully functional PSII. Photosynthetic performance (PI) increased at lower Co2+ concentrations while higher Co2+ concentrations caused its decrease. Detailed analysis of PSII functioning revealed differences in absorption of light energy, trapping and dissipation of excitation energy as well as efficiency of the conversion of excitation energy to electron transport. Although there were no changes in H2O2 level, the increased level of lipid peroxidation was measured. This indicates that some other reactive oxygen species besides H2O2 might be responsible for increased lipid peroxidation. Also, the photosynthesis up regulation at lower Co2+ concentrations might indicate higher demands of treated plants for ATP and NADPH due to activation of defense mechanisms against Co2+ toxicity.

cobalt; Lemna; lipid peroxidation; photosynthesis; stress

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