title: Fast and reversible response of thylakoid-associated polyamines during and after UV-B stress: a comparative study of the wild type and a mutant lacking chlorophyll b of unicellular green alga Scenedesmus obliquus.
abstract: The functional and biochemical aspects of the photosynthetic apparatus in response to UV-B radiation were examined in unicellular oxygenic algae Scenedesmus obliquus. The wild type (Wt) and a chlorophyll b-less mutant (Wt-lhc) were used as a specific tool for the understanding of antenna role. Photosynthesis was monitored during and after UV-B stress by time resolved fluorescence spectroscopy and polarography. Carotenoids, such as neoxanthin, loroxanthin, lutein, violaxanthin, antheraxanthin, zeaxanthin, alpha- and beta-carotene, cellular and thylakoid-associated putrescine, spermidine, spermine and subcomplexes of light-harvesting complex (LHCII) of photosystem II (PSII) were investigated to assess their possible involvement in response to UV-B. Oxygen evolution depression by UV-B was higher in the Wt-lhc mutant than in the Wt. Photosynthesis recovery occurred in the Wt, but not in the mutant. The dissipation of excess excitation energy during UV-B stress was accompanied by changes in the thylakoid-associated polyamines which were much higher than changes in xanthophylls. We conclude that, at least in the unicellular green alga S. obliquus, mutants lacking chlorophyll b have significant lower capacity for recovery after UV-B stress. In addition, the comparison of xanthophylls and thylakoid-associated polyamines reveals that the latter are more responsive to UV-B stress and in a reversible manner.
authors.affiliation: Department of Biology, University of Crete, PO Box 2208, Heraklion, Crete 71409, Greece.
authors.forename: Liliana
authors.initials: L
authors.lastname: Sfichi-Duke
authors.forename: Nikolaos E
authors.initials: NE
authors.lastname: Ioannidis
authors.forename: Kiriakos
authors.initials: K
authors.lastname: Kotzabasis
mesh_terms: D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D006706:Homeostasis; D009154:Mutation; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011048:Polarography; D011073:Polyamines / Q000378:metabolism*; D044444:Scenedesmus / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D045332:Photosystem II Protein Complex; D011073:Polyamines; D002734:Chlorophyll; D002338:Carotenoids; C037184:chlorophyll b