title: Response of Spirodela polyrhiza to cerium: subcellular distribution, growth and biochemical changes.
abstract: Rare earth elements are new and emerging contaminants in freshwater systems. Greater duckweed (Spirodela polyrhiza L.) is a common aquatic plant widely used in phytotoxicity tests for xenobiotic substances. In this study, the cerium (Ce) accumulation potential, the distribution of Ce in bio-molecules, and ensuing biochemical responses were investigated in greater duckweed fronds when they were exposed to Ce (0, 10, 20, 40, and 60μM). There was a concentration dependent increase in Ce accumulation, which reached a maximum of 67mgg-1of dry weight (DW) at 60μM Ce after 14 d. The Ce concentrations in bio-macromolecules followed the order: cellulose and pectin > proteins > polysaccharides > lipids. In response to Ce exposure, significant chlorosis; declines in growth, photosynthetic pigment and protein contents; and cell death were noted at the highest Ce concentration. Photosystem II inhibition, degradation of the reaction center protein D1, and damage to chloroplast ultrastructure were observed in Ce treated S. polyrhiza fronds, as revealed by chlorophyll a fluorescence transients, immunoblotting, and transmission electron microscopy (TEM). O2.-accumulation and malondialdehyde (MDA) content in the treated fronds increased in a concentration dependent manner, which indicated that oxidative stress and unsaturated fatty acids (C18:3) were specifically affected by Ce exposure. These results suggest Ce exerts its toxic effects on photosynthesis, with a primary effect on PS II, through oxidative stress.
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China. Electronic address: xuqinsong@njnu.edu.cn.
authors.forename: Qinsong
authors.initials: Q
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Weiyue
authors.initials: W
authors.lastname: Chu
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Chunlei
authors.initials: C
authors.lastname: Su
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Hu
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Lu
authors.affiliation: College of Life Science, Nanjing Normal University, Nanjing 210023, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Zhang
mesh_terms: D029064:Araceae / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D016923:Cell Death; D002563:Cerium / Q000378:metabolism* / Q000633:toxicity; D002734:Chlorophyll / Q000031:analogs & derivatives / Q000378:metabolism; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D017753:Ecosystem; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005618:Fresh Water; D008315:Malondialdehyde / Q000378:metabolism; D018384:Oxidative Stress; D010788:Photosynthesis / Q000187:drug effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves; D011134:Polysaccharides / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000378:metabolism* / Q000633:toxicity
chemical_list: D005231:Fatty Acids, Unsaturated; D045332:Photosystem II Protein Complex; D011134:Polysaccharides; D014874:Water Pollutants, Chemical; D002734:Chlorophyll; C085815:chlorophyll a'; D002563:Cerium; D008315:Malondialdehyde; D000077194:Chlorophyll A
keywords: Biological molecules; Cerium; Greater duckweed; Lipid peroxidation; Photosystem II