title: Effects of boron deficiency on major metabolites, key enzymes and gas exchange in leaves and roots of Citrus sinensis seedlings.
abstract: Boron (B) deficiency is a widespread problem in many crops, including Citrus. The effects of B-deficiency on gas exchange, carbohydrates, organic acids, amino acids, total soluble proteins and phenolics, and the activities of key enzymes involved in organic acid and amino acid metabolism in 'Xuegan' [Citrus sinensis (L.) Osbeck] leaves and roots were investigated. Boron-deficient leaves displayed excessive accumulation of nonstructural carbohydrates and much lower CO2 assimilation, demonstrating feedback inhibition of photosynthesis. Dark respiration, concentrations of most organic acids [i.e., malate, citrate, oxaloacetate (OAA), pyruvate and phosphoenolpyruvate] and activities of enzymes [i.e., phosphoenolpyruvate carboxylase (PEPC), NAD-malate dehydrogenase, NAD-malic enzyme (NAD-ME), NADP-ME, pyruvate kinase (PK), phosphoenolpyruvate phosphatase (PEPP), citrate synthase (CS), aconitase (ACO), NADP-isocitrate dehydrogenase (NADP-IDH) and hexokinase] involved in glycolysis, the tricarboxylic acid (TCA) cycle and the anapleurotic reaction were higher in B-deficient leaves than in controls. Also, total free amino acid (TFAA) concentration and related enzyme [i.e., NADH-dependent glutamate 2-oxoglutarate aminotransferase (NADH-GOGAT) and glutamate OAA transaminase (GOT)] activities were enhanced in B-deficient leaves. By contrast, respiration, concentrations of nonstructural carbohydrates and three organic acids (malate, citrate and pyruvate), and activities of most enzymes [i.e., PEPC, NADP-ME, PK, PEPP, CS, ACO, NAD-isocitrate dehydrogenase, NADP-IDH and hexokinase] involved in glycolysis, the TCA cycle and the anapleurotic reaction, as well as concentration of TFAA and activities of related enzymes (i.e., nitrate reductase, NADH-GOGAT, glutamate pyruvate transaminase and glutamine synthetase) were lower in B-deficient roots than in controls. Interestingly, leaf and root concentration of total phenolics increased, whereas that of total soluble protein decreased, in response to B-deficiency. In conclusion, respiration, organic acid (i.e., glycolysis and the TCA cycle) metabolism, the anapleurotic pathway and amino acid biosynthesis were upregulated in B-deficient leaves with excessive accumulation of carbohydrates to 'consume' the excessive carbon available, but downregulated in B-deficient roots with less accumulation of carbohydrates to maintain the net carbon balance.
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Yi-Bin
authors: YB
authors: Lu
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Lin-Tong
authors: LT
authors: Yang
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Yan
authors: Y
authors: Li
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Jing
authors: J
authors: Xu
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Tian-Tai
authors: TT
authors: Liao
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China.
authors: Yan-Bin
authors: YB
authors: Chen
authors: College of Resource and Environmental Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, China Fujian Key Laboratory for Plant Molecular and Cell Biology, Fujian Agriculture and Forestry University, Fuzhou 350002, China lisongchen2002@hotmail.com lisongchen@fafu.edu.cn.
authors: Li-Song
authors: LS
authors: Chen
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D001895:Boron / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D002264:Carboxylic Acids / Q000378:metabolism; D032084:Citrus sinensis / Q000201:enzymology / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000201:enzymology / Q000502:physiology; D018517:Plant Roots / Q000201:enzymology / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D036226:Seedlings / Q000201:enzymology / Q000502:physiology
chemical_list: D000596:Amino Acids; D002264:Carboxylic Acids; D002244:Carbon; D001895:Boron
keywords: amino acid; carbohydrate; organic acid