UV-B Absorbing and Bioactive Secondary Compounds in Lichens Xanthoria Elegans and Xanthoria Parietina: a Review
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CZECH POLAR REPORTS 10 (2): 252-262, 2020 UV-B absorbing and bioactive secondary compounds in lichens Xanthoria elegans and Xanthoria parietina: A review Vilmantas Pedišius Instrumental Analysis Open Access Centre, Faculty of Natural Sciences, Vytautas Magnus university, Vileikos g. 8-212, LT-44404, Kaunas, Lithuania Abstract Secondary metabolites are the bioactive compounds of plants which are synthesized during primary metabolism, have no role in the development process but are needed for defense and other special purposes. These secondary metabolites, such as flavonoids, terpenes, alkaloids, anthraquinones and carotenoids, are found in Xanthoria genus li- chens. These lichens are known as lichenized fungi in the family Teloschistaceae, which grows on rock and produce bioactive compounds. A lot of secondary compounds in plants are induced by UV (100-400 nm) spectra. The present review showcases the present identified bioactive compounds in Xanthoria elegans and Xanthoria parietina lichens, which are stimulated by different amounts of UV-B light (280-320 nm), as well as the biochemistry of the UV-B absorbing compounds. Key words: UV-B, Xanthoria parietina, Xanthoria elegans, parietin, phenolic compounds, carotenoids, anthraquinone DOI: 10.5817/CPR2020-2-19 Introduction UV-B light plays an important role in membranes and DNA (Gu et al. 2010, nature, yet it may cause adverse effects Yavaş et al. 2020). For example, enhanced in high amounts of it. Chlorofluorocarbons concentrations of the indole 1-methoxy-3- are mainly responsible for the depletion indolylmethyl glucosinolate were reported of ozone layer which results in an increase to result in the formation of DNA adducts of UV-B (280 to 320 nm) irradiation of (Glatt et al. 2011). However, the synthe- earth’s environment and cause adverse ef- sized plant secondary metabolites (PSMs) fects on flora and crops (Yavaş et al. can provide benefits for both ends of the 2020). Though according to NASA, the bio- based food chain – humans and plants ozone hole is on its way to recovery, it will alike (Schreiner et al. 2012). still be a considerable time before UV-B Many secondary metabolites, like flavo- levels reach pre-industrial limits (Takshak noids, alkaloids, terpenoids, phenolics, ca- and Agrawal 2019). Moreover, UV-B ra- rotenoids, glucoseinolates, anthraquinones, diation is harmful to plants, animals and hu- sterols, lignin, etc., are UV-B absorbing mans, specifically to their proteins, lipids, compounds (Gu et al. 2010, Takshak and ——— Received August 8, 2020, accepted November 19, 2020. *Corresponding author: V. Pedišius <[email protected]> 252 V. PEDIŠIUS Agrawal 2019, Yavaş et al. 2020). The This review is focused on secondary amount of UV-B radiation plants were ex- metabolites that absorb UV-B radiation in posed to plays a big role in synthesis of Xanthoria elegans and Xanthoria pari- secondary metabolites. A sufficient amount etina. The two species are reported to be of UV-B may increase the amount of sec- rich in UV-B screening compounds (see ondary metabolites; however, an overex- e.g. Al-Amoody et al. 2000, Goga et al. posure usually decreases their amount. 2020). Geographical distribution of Xanthoria elegans and Xanthoria parietina in Polar Regions of the Earth The differences between lichen species ples increased with decreasing latitude of growing in Polar and in Alpine Regions their sampling location, which may imply can be looked at in two ways: UV irradi- that the synthesis of pigments is habitat ance and temperature. The Alpine popu- specific. Arctic populations therefore main- lations receive 3–5 times higher UV-B tain a high level of screening pigments in irradiance than their Arctic counterparts spite of low ambient UV-B, and the stud- from Arctic Svalbard (Norway) because ied lichen species presumably may tolerate of latitudinal and altitudinal gradients in an increase in UV-B radiation due to the UV-B irradiance (Nybakken et al. 2004). predicted thinning of the ozone layer over Temperature also has a significant ef- polar areas (Nybakken et al. 2004). En- fect on relative growth rate (RGR) such hanced metabolic activity might also be an that of X. elegans. Originating from sites adaptation for growth in colder climates with lower mean annual temperatures, (Murtagh et al. 2002). Antarctic higher X. elegans had significantly higher RGRs plants and autotrophic organisms have a at all test temperatures between 2 and high capacity to synthetize photoprotective 18°C (Murtagh et al. 2002). The parietin secondary compounds when exposed to in- synthesis in these parietin-deficient sam- creased levels of UV-B (Estêvao 2015). UV-B irradiation in vitro The existence of a specific UV-B pho- samples were exposed to different doses of toreceptor, which detects UV-B radiation UV-B (280–320 nm) - low (0.7 W m-2), and initiates a signaling cascade, was pro- medium (1.5 W m-2) and high (3.0 W m-2) posed several decades ago by Wellmann for 5 days. Results showed that when ex- (1983). However, it is only in recent years posed to a low dose of UV-B radiation or a that substantial progress was made in short-term treatment, lichen species exhib- identifying this photoreceptor and compo- ited an increase in UV-B screening pig- nents of the downstream signaling path- ments in order to protect the lichen pho- way (Schreiner et al. 2012). tobiont against UV-B damage (Estêvao Many factors are involved in secondary 2015). Thus, photosynthetic secondary me- metabolite synthesis under UV-B expo- tabolites (PSMs) are increasingly recog- sure. The intensity and time (for which nized and made for the use of sunscreens the sample is exposed to UV-B radiation) and cosmetics (Takshak and Agrawal 2019). plays an important role. In the study of However, Estêvao’s study has shown that a Estêvao (2015), algal lichen X. elegans decrease of UV-B screening compounds 253 LICHEN UV-B SCREENS occurred after exposition to a high dose of creased under all UV-B treatments by UV-B radiation or a long-term treatment. 9%–18%, 28%–126%, and 80%–169%, -1 It is also important to be mindful of UV respectively, where 1 h·day for 2 days light exposure, because it is useful in opti- UV-B radiation was the optimal condition mizing total biomass and metabolite pro- (Dou et al. 2019). Strong positive correla- duction in controlled environments. Brech- tions between the concentrations of phe- ner et al. (2011) preformed dose treat- nolic compounds under the highest UV-B ments with 55- day-old Hypericum perfo- dose (102 kJ·m-2·day-1) in sub-chronic ex- -2 -1 ratum grown under 400 µmol·m ·s PAR periments were shown, where four differ- for 16 h a day. Three UV light treatments ent UV-B doses (8.5, 34, 68, 102 kJ·m-2· were evaluated: a single dose, a daily dose day-1) were used over 6 days (Mosadegh et and an increasing daily dose. A daily dose al. 2018). and an increasing daily dose did not pro- In natural environment of the Hima- duce significantly higher increase in sec- layan region, X. elegans was exposed to ondary metabolites compared to the single natural radiation over the time of 120 h. dose treatments. (Brechner et al. 2011). The maximum average UV-B irradiance In another study, basil (Ocimum basilicum) (4.38 MED/h – Minimal Erythemal Dose was exposed to UV-B radiation dose of per hour) was recorded at 72 h, whereas -2 -1 -2 -1 16 µmol·m ·s (equal to 18.7 kJ·m ·h ). minimum was 1.72 MED/h at 120 h. The Concentrations of anthocyanin, phenolics, average was 3.426 MED/h. and flavonoids in green basil leaves in- Use of UV-B radiation treatments Targeted low dosage UV-B radiation arrest (Glatt et al. 2011). treatments as emerging technology may One of the dominant compounds in the be used to generate fruit, vegetables, and Xanthoria genus is parietin. Parietin, ex- herbs enriched with secondary plant me- tracted from X. parietina while dissolved tabolites for either fresh consumption or as in ethanol, strongly absorbs UV-B radia- a source for functional foods and nu- tion (absorption peak at 288 nm), followed traceuticals, resulting in increased inges- by a minimum absorption in the UV-A tion of these health-promoting substances range, and a second peak at blue wave- (Schreiner et al. 2012, Takshak and Agra- lengths (431 nm) (Gauslaa and Ustvedt wal 2019). The UV-B induced secondary 2003). Field experiments with extracted metabolites are active components of herb- (parietin deficient) X. elegans thalli culti- al drugs (Gu et al. 2010). For example, vated under various filters showed that increased concentrations of the aliphatic UV-B was essential for the induction of 4-methylsulfinylbutyl glucosinolate is as- parietin synthesis – only 12% of the orig- sociated with anti-carcinogenic properties inal content of parietin was resynthesized due to this metabolite’s effect on the up- with the PAR (photosynthetically active regulation of phase II detoxification en- radiation) treatment, whereas as much as zymes and inhibition of cell proliferation 35% was resynthesized with the PAR + by either inducing apoptosis or cell cycle UV treatment (Nybakken et al. 2004). 254 V. PEDIŠIUS Biochemistry of UV-induction of UV-B absorbing compounds The synthesis of compounds that are GS from tryptophan, and aromatic GS UV-B absorbing (flavonoids, flavanol glu- from phenylalanine (Zu et al. 2010). Ali- cosides and hydrocycinnamates) share the phatic 4-methylsulfinylbutyl glucosinolate phenylpropanoid biosynthesis pathway. is associated with anticarcinogenic proper- The pathway has the amino acid phenyl- ties due to this metabolite’s effect on the alanine as the substrate. The enzyme phen- upregulation of phase II detoxification en- ylalanine ammonia lyase (PAL) catalyses zymes and inhibition of cell proliferation the formation of the cinnamic acid by by either inducing apoptosis or cell cy- non-oxidative deamination of the amino cle alteration.