Activity of superoxide dismutase and catalase in lichens with different composition of photobionts

Data on the activity of catalase and superoxide dismutase in the thalli of the cyanolichen Peltigera praetextata and the green algal lichen Hypogymnia physodes (See Fig. 1) at different ontogenetic conditions are not available in the literature. At the same time, the study of antioxidant system of lichen thalli with different photobionts during ontogenesis is relevant and can contribute to understanding the mechanisms of adaptation of symbionts to changing environmental conditions, and also serve as indicators of the functional state of the organism. The aim of the study was to investigate the activity of catalase and superoxide dismutase enzymes in lichen thalli P. praetextata and H. physodes at different stages of ontogenesis. P. praetextata and H. physodes thalli samples were collected from aspen and pine trunks under similar ecological conditions of mixed aspen-spruce communities in the middle taiga (62°15'15.9'' N, 33°58746.1" E, 61°50'17'' N, 34°23'13'' E, the Republic of Karelia) and northern taiga (64°34'13.9' N, 43°15'48'' E, Arkhangelsk Oblast, 64° 33'19'' N, 30°20'46'' E, the Republic of Karelia). Based on morphological features, thalli samples were divided into groups of different age. P. praetextata thalli were divided into 3 groups: virginal (pregenerative, young thalli without reproduction structures), generative (thalli with apothecia and phyllidia - structures of vegetative reproduction), and senile thalli (thalli with signs of degradation over a larger area). H. physodes thalli were divided into 2 groups: virginil and senile thalli; generative thalli with apothecia are extremely rare in the study areas. Catalase activity measured based on enzymatic degradation of hydrogen peroxide, superoxide dismutase activity was determined spectrophotometrically by inhibition of photoreduction of nitroblue tetrazolium, protein content was determined by the method Bradford. Statistical analysis of the data was carried out using one-way analysis of variance. The protein content (mg/g dry mass) in P. praetextata thalli within the studied sample averaged 1.12 ± 0.09, in H. physodes thalli - 2.45 ± 0.32. The activity of superoxide dismutase (units/mg of protein) in thalli of P. praetextata reached an average of 0.34 ± 0.12, in thalli of H. physodes - 0.09 ± 0.01. The values of catalase activity (μmol H2O2μg protein) in P. praetextata thalli averaged 2.06 ± 0.48, H. physodes - 0.49 ± 0.07. For the thalli of the cyanolichen P. praetextata, a lower (2 times) protein content (See Fig. 2) and a higher (4-5 times) activity of superoxide dismutase (See Fig. 3) and catalase (See Fig. 4) were found in compared with the chlorobiont lichen H. physodes. The species P. praetextata belongs to the group of cyanolichens, and its photobiont is cyanobacteria of the genus Nostoc located in the algal layer of the thallus. In both lichen species, the maximum values of catalase activity were established for virginal thalli, and the minimum values for senile thalli. Perhaps this is due to the high intensity of "growth respiration" of young lichen thalli, which leads to the formation of reactive oxygen species. Differences in the activity of superoxide dismutase in thalli of different ontogenetic stages in the studied species were not shown. In the thalli of P. praetextata and H. physodes, the activity of catalase in thalli from the northern taiga communities is higher than in the thalli of the middle taiga, while the activity of superoxide dismutase, on the contrary, was on average higher in the lichen thalli of the middle taiga. This might be due to variability in the intensity of photosynthesis and respiration along the latitudinal gradient. In lichens, catalase activity can be a marker of mycobiont respiration, and superoxide dismutase activity is a marker of photobiont photosynthesis. The question of contribution of the fungal or algal components of the lichen thallus to the activity of antioxidant enzymes remains open. The article contains 4 Figures, 51 References. The authors are grateful to K.M. Nikerova, Senior Researcher, Analytical Laboratory, KarRC RAS (Petrozavodsk) for valuable consultations on the specifics of the methods used in the study, as well as to the master of the Institute of Biology, Ecology and Agrotechnologies of PetrSU M.A. Chigir for help in sample preparation. The Authors declare no conflict of interest.

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