High‐Light Stress and Photoprotection in Umbilicaria antarctica Monitored by Chlorophyll Fluorescence Imaging and Changes in Zeaxanthin and Glutathione

Abstract

The effect of high light on spatial distribution of chlorophyll (Chl) fluorescence parameters over a lichen thallus (Umbilicaria antarctica) was investigated by imaging of Chl fluorescence parameters before and after exposure to high light (1500 micro mol m (-2) s (-1), 30 min at 5 degrees C). False colour images of F (V)/F (M) and Phi (II) distribution, taken over thallus with 0.1 mm (2) resolution, showed that maximum F (V)/F (M) and Phi (II) values were located close to the thallus centre. Minimum values were typical for thallus margins. After exposure to high light, a differential response of F (V)/F (M) and Phi (II) was found. The marginal thallus part exhibited a loss of photosynthetic activity, manifested as a lack of Chl fluorescence signal, and close-to-centre parts showed a different extent of F (V)/F (M) and Phi (II) decrease. Subsequent recovery in the dark led to a gradual return of F (V)/F (M) and Phi (II) to their initial values. Fast (30 min) and slow (1 - 22 h) phase of recovery were distinguished, suggesting a sufficient capacity of photoprotective mechanisms in U. antarctica to cope with low-temperature photoinhibition. Glutathione and xanthophyll cycle pigments were analyzed by HPLC. High light led to an increase in oxidized glutathione (GSSG), and a conversion of violaxanthin to zeaxanthin, expressed as their de-epoxidation state (DEPS). The responses of GSSG and DEPS were reversible during subsequent recovery in the dark. GSSG and DEPS were highly correlated to non-photochemical quenching (NPQ), indicating involvement of these antioxidants in the resistance of U. antarctica to high-light stress. Heterogeneity of Chl fluorescence parameters over the thallus and differential response to high light are discussed in relation to thallus anatomy and intrathalline distribution of the symbiotic alga Trebouxia sp.

Cytotoxic activity of physodic acid and acetone extract fromHypogymnia physodesagainst breast cancer cell lines

“…For example, Mitrović et al (2011) and Stojanović et al (2010) reported the IC 50 values for methanolic extracts (45.57 lg/mL and 79.70 lg/mL), and reported the percentage of inhibition of DPPH radicals by methanolic (73.18%), acetone (60.18%) and aqueous (30.98%) extracts from H. physodes. Climatic conditions, such as high light intensity, high temperature and air pollution, have been shown to play important roles in the production of lichen metabolites and to influence their biological properties (Bartak et al 2004;Weissman et al 2006;Millot et al 2007). Thus, the biological properties of extract from the thalli of H. physodes grown in Poland may differ from those of H. physodes in other countries, where the lichen may be exposed to other environmental factors.…”

Antioxidant properties of some lichen species

“…Numerous studies showed that environmental factors play an important role in antioxidant activity of lichens. Extreme environmental factors such as high light, air pollution, desiccation, rehydration and high temperature affecting decreased antioxidant activity and reducing synthesis of antioxidants by lichens (Bartak et al 2004;Weissman et al 2005Weissman et al , 2006. Antioxidant activity of some other lichen was studied by other researchers.…”

Photoinhibition of photosynthesis in Antarctic lichen Usnea antarctica. I. Light intensity- and light duration-dependent changes in functioning of photosystem II

“…Among them, formation of zeaxanthin during the initial phases of photoinhibition is well known (Demmig-Adams et al (1990b) and documented for number of chlorolichens from polar regions, e.g. Usnea antarctica (Barták et al 2003), Umbilicaria antarctica (Barták et al 2004). This effect, however, was not observed in cyanolichens.…”