Response to cobalt toxicity in lichen Pseudevernia furfuracea; uptake, photosynthetic quantum yield, membrane integrity and deoxyribonucleic acid fragmentation

Objectives: This study aims to examine the toxic potential of Cobalt (Co) on photosystem II photosynthetic quantum yield, membrane integrity, and deoxyribonucleic acid (DNA) fragmentation formation. Materials and methods: Oligonucleosomal DNA fragmentation was detected by terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assay. Lipid peroxidation was determined with malondialdehyde analyzing. Results: The Fv/Fm ratio decreased in Pseudevernia furfuracea following exposure to various concentrations of Co (NO 3 ) 2 (5, 15 and 30 mM) for one, three and 24 hours. Co2+-treatment caused the accumulation of Co in lichen, induced severe oxidative stress by the generation of hydrogen peroxide, impaired the membrane integrity, and induced lipid peroxidation as measured by malondialdehyde. Samples treated with 15 mM and 30 mM of Co (NO3)2 had higher percentage of cell death than 5 mM-treated group. Conclusion: To our knowledge, this is the first study detecting a high rate of DNA fragmentation in situ in phycobiont layer of Pseudevernia furfuracea; while it reveals that mycobiont layer has a lower rate of TUNEL-positive cells. It has been concluded that Co exposure results in impaired photosynthesis accompanied by oxidative stress and DNA fragmentation in Pseudevernia furfuracea; all these effects were concentration-dependent.

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