title: Ultraviolet-B component of sunlight stimulates photosynthesis and flavonoid accumulation in variegated Plectranthus coleoides leaves depending on background light.
abstract: We used variegated Plectranthus coleoides as a model plant with the aim of clarifying whether the effects of realistic ultraviolet-B (UV-B) doses on phenolic metabolism in leaves are mediated by photosynthesis. Plants were exposed to UV-B radiation (0.90 W m(-2) ) combined with two photosynthetically active radiation (PAR) intensities [395 and 1350 μmol m(-2)  s(-1) , low light (LL) and high light (HL)] for 9 d in sun simulators. Our study indicates that UV-B component of sunlight stimulates CO2 assimilation and stomatal conductance, depending on background light. UV-B-specific induction of apigenin and cyanidin glycosides was observed in both green and white tissues. However, all the other phenolic subclasses were up to four times more abundant in green leaf tissue. Caffeic and rosmarinic acids, catechin and epicatechin, which are endogenous peroxidase substrates, were depleted at HL in green tissue. This was correlated with increased peroxidase and ascorbate peroxidase activities and increased ascorbate content. The UV-B supplement to HL attenuated antioxidative metabolism and partly recovered the phenolic pool indicating stimulation of the phenylpropanoid pathway. In summary, we propose that ortho-dihydroxy phenolics are involved in antioxidative defence in chlorophyllous tissue upon light excess, while apigenin and cyanidin in white tissue have preferentially UV-screening function.
authors.affiliation: Institute for Multidisciplinary Research, University of Belgrade, Belgrade, 11000, Serbia.
authors.forename: Marija
authors.initials: M
authors.lastname: Vidović
authors.forename: Filis
authors.initials: F
authors.lastname: Morina
authors.forename: Sonja
authors.initials: S
authors.lastname: Milić
authors.forename: Bernd
authors.initials: B
authors.lastname: Zechmann
authors.forename: Andreas
authors.initials: A
authors.lastname: Albert
authors.forename: Jana Barbro
authors.initials: JB
authors.lastname: Winkler
authors.forename: Sonja
authors.initials: S
authors.lastname: Veljović Jovanović
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000528:radiation effects; D002736:Chloroplasts / Q000528:radiation effects / Q000648:ultrastructure; D005419:Flavonoids / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects*; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects*; D031346:Plectranthus / Q000378:metabolism / Q000528:radiation effects*; D050050:Protein Carbonylation / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D010636:Phenols; D010860:Pigments, Biological; D002734:Chlorophyll; D002245:Carbon Dioxide
keywords: UV-B radiation; ascorbate; chloroplast ultrastructure; cyanidin; flavonoids; high light; photosynthesis; variegated plants