title: Proteomic analysis of Citrus sinensis roots and leaves in response to long-term magnesium-deficiency.
abstract: BACKGROUND
  Magnesium (Mg)-deficiency is frequently observed in Citrus plantations and is responsible for the loss of productivity and poor fruit quality. Knowledge on the effects of Mg-deficiency on upstream targets is scarce. Seedlings of 'Xuegan' [Citrus sinensis (L.) Osbeck] were irrigated with Mg-deficient (0 mM MgSO4) or Mg-sufficient (1 mM MgSO4) nutrient solution for 16 weeks. Thereafter, we first investigated the proteomic responses of C. sinensis roots and leaves to Mg-deficiency using two-dimensional electrophoresis (2-DE) in order to (a) enrich our understanding of the molecular mechanisms of plants to deal with Mg-deficiency and (b) understand the molecular mechanisms by which Mg-deficiency lead to a decrease in photosynthesis.
  
  
  RESULTS
  Fifty-nine upregulated and 31 downregulated protein spots were isolated in Mg-deficient leaves, while only 19 upregulated and 12 downregulated protein spots in Mg-deficient roots. Many Mg-deficiency-responsive proteins were involved in carbohydrate and energy metabolism, followed by protein metabolism, stress responses, nucleic acid metabolism, cell wall and cytoskeleton metabolism, lipid metabolism and cell transport. The larger changes in leaf proteome versus root one in response to Mg-deficiency was further supported by our observation that total soluble protein concentration was decreased by Mg-deficiency in leaves, but unaffected in roots. Mg-deficiency had decreased levels of proteins [i.e. ribulose-1,5-bisphosphate carboxylase (Rubisco), rubisco activase, oxygen evolving enhancer protein 1, photosynthetic electron transfer-like protein, ferredoxin-NADP reductase (FNR), aldolase] involved in photosynthesis, thus decreasing leaf photosynthesis. To cope with Mg-deficiency, C. sinensis leaves and roots might respond adaptively to Mg-deficiency through: improving leaf respiration and lowering root respiration, but increasing (decreasing) the levels of proteins related to ATP synthase in roots (leaves); enhancing the levels of proteins involved in reactive oxygen species (ROS) scavenging and other stress-responsive proteins; accelerating proteolytic cleavage of proteins by proteases, protein transport and amino acid metabolism; and upregulating the levels of proteins involved in cell wall and cytoskeleton metabolism.
  
  
  CONCLUSIONS
  Our results demonstrated that proteomics were more affected by long-term Mg-deficiency in leaves than in roots, and that the adaptive responses differed between roots and leaves when exposed to long-term Mg-deficiency. Mg-deficiency decreased the levels of many proteins involved in photosynthesis, thus decreasing leaf photosynthesis.
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 263618957@qq.com.|College of Life Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 263618957@qq.com.|Institute of Horticultural Plant Physiology, Biochemistry, and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 263618957@qq.com.
authors.forename: Hao-Yang
authors.initials: HY
authors.lastname: Peng
authors.affiliation: Institute of Materia Medica, Fujian Academy of Medical Sciences, Fuzhou, 350001, China. qiyiping2008@hotmail.com.
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Qi
authors.affiliation: Department of Horticultural Science, Kyungpook National University, Daegu, 702-701, ROK. jl425@knu.ac.kr.
authors.forename: Jinwook
authors.initials: J
authors.lastname: Lee
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. talstoy@sina.com.|Institute of Horticultural Plant Physiology, Biochemistry, and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. talstoy@sina.com.
authors.forename: Lin-Tong
authors.initials: LT
authors.lastname: Yang
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 6253730@163.com.|Institute of Horticultural Plant Physiology, Biochemistry, and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. 6253730@163.com.
authors.forename: Peng
authors.initials: P
authors.lastname: Guo
authors.affiliation: College of Life Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. jianghx@163.com.|Institute of Horticultural Plant Physiology, Biochemistry, and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. jianghx@163.com.
authors.forename: Huan-Xin
authors.initials: HX
authors.lastname: Jiang
authors.affiliation: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|Institute of Horticultural Plant Physiology, Biochemistry, and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|Fujian Key Laboratory for Plant Molecular and Cell Biology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.|The Higher Educational Key Laboratory of Fujian Province for Soil Ecosystem Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. lisongchen2002@hotmail.com.
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D032084:Citrus sinensis / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000032:analysis* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D040901:Proteomics; D013312:Stress, Physiological
chemical_list: D010940:Plant Proteins; D002245:Carbon Dioxide; D008274:Magnesium