title: Interactive effects of UV radiation and reduced precipitation on the seasonal leaf phenolic content/composition and the antioxidant activity of naturally growing Arbutus unedo plants.
abstract: The effects of UV radiation and rainfall reduction on the seasonal leaf phenolic content/composition and antioxidant activity of the Mediterranean shrub Arbutus unedo were studied. Naturally growing plants of A. unedo were submitted to 97% UV-B reduction (UVA), 95% UV-A+UV-B reduction (UV0) or near-ambient UV levels (UVBA) under two precipitation regimes (natural rainfall or 10-30% rainfall reduction). Total phenol, flavonol and flavanol contents, levels of eight phenols and antioxidant activity [DPPH(●) radical scavenging and Cu (II) reducing capacity] were measured in sun-exposed leaves at the end of four consecutive seasons. Results showed a significant seasonal variation in the leaf content of phenols of A. unedo, with the lowest values found in spring and the highest in autumn and/or winter. Leaf ontogenetic development and/or a possible effect of low temperatures in autumn/winter may account for such findings. Regardless of the watering regime and the sampling date, plant exposure to UV-B radiation decreased the total flavanol content of leaves, while it increased the leaf content in quercitrin (the most abundant quercetin derivative identified). By contrast, UV-A radiation increased the leaf content of theogallin, a gallic acid derivative. Other phenolic compounds (two quercetin derivatives, one of them being avicularin, and one kaempferol derivative, juglanin), as well as the antioxidant activity of the leaves, showed different responses to UV radiation depending on the precipitation regime. Surprisingly, reduced rainfall significantly decreased the total amount of quantified quercetin derivatives as well as the DPPH scavenging activity in A. unedo leaves. To conclude, present findings indicate that leaves of A. unedo can be a good source of antioxidants throughout the year, but especially in autumn and winter.
authors.affiliation: Laboratory of Food Chemistry & Technology, School of Chemistry, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece. Electronic address: niknen@chem.auth.gr.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Nenadis
authors.affiliation: Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi s/n E-17071, Girona, Spain. Electronic address: laura.llorens@udg.edu.
authors.forename: Laura
authors.initials: L
authors.lastname: Llorens
authors.affiliation: Laboratory of Food Chemistry & Technology, School of Chemistry, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece.
authors.forename: Agathi
authors.initials: A
authors.lastname: Koufogianni
authors.affiliation: Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi s/n E-17071, Girona, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Díaz
authors.affiliation: Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi s/n E-17071, Girona, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Font
authors.affiliation: Physics Department, Polytechnic II Faculty, University of Girona, Campus de Montilivi s/n, E-17071, Girona, Spain.
authors.forename: Josep Abel
authors.initials: JA
authors.lastname: Gonzalez
authors.affiliation: Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi s/n E-17071, Girona, Spain.
authors.forename: Dolors
authors.initials: D
authors.lastname: Verdaguer
mesh_terms: D000975:Antioxidants / Q000032:analysis / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D055864:Droughts; D029791:Ericaceae / Q000737:chemistry / Q000254:growth & development / Q000528:radiation effects*; D044948:Flavonols / Q000032:analysis / Q000737:chemistry; D010636:Phenols / Q000032:analysis / Q000737:chemistry*; D010788:Photosynthesis / Q000528:radiation effects; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D011794:Quercetin / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry; D012621:Seasons; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D044948:Flavonols; D010636:Phenols; C012526:quercitrin; D011794:Quercetin
keywords: Antioxidant activity; Arbutus unedo; Drought; Phenolic compounds; UV-A radiation; UV-B radiation