title: Organic acids promote the uptake of lanthanum by barley roots.
abstract: Organic acids play an important role in metal uptake by, and accumulation in, plants. However, the relevant mechanisms remain obscure. Acetic, malic and citric acids increased the uptake of lanthanum (La) by barley (Hordeum vulgare) roots and enhanced La content in shoots under hydroponic conditions. Concentration-dependent net La influx in the absence and presence of organic acids yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The saturable component followed Michaelis-Menten kinetics. The K(m) values were similar; however, the V(max) values in the presence of acetic, malic and citric acids were 4.3, 2.8, 1.5-times that of the control, respectively. Enhanced uptake of La by organic acids was mediated mainly, but not solely, by Ca(2+) channels. X-ray absorption spectroscopic techniques provided evidence of La-oxygen environment and established that La(III) was coordinated to 11 oxygen atoms that are likely to be involved in the binding of La(III) to barley roots via carboxylate groups and hydration of La(III).
authors.affiliation: Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, PO Box 2871, Beijing 100085, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Han
authors.forename: Xiao-Quan
authors.initials: XQ
authors.lastname: Shan
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Ya-Ning
authors.initials: YN
authors.lastname: Xie
authors.forename: Zhi-Guo
authors.initials: ZG
authors.lastname: Pei
authors.forename: Shu-Zhen
authors.initials: SZ
authors.lastname: Zhang
authors.forename: Yong-Guan
authors.initials: YG
authors.lastname: Zhu
authors.forename: Bei
authors.initials: B
authors.lastname: Wen
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D000144:Acids, Acyclic / Q000494:pharmacology*; D019343:Citric Acid / Q000494:pharmacology; D001467:Hordeum / Q000187:drug effects* / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D007811:Lanthanum / Q000378:metabolism*; D008293:Malates / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D000144:Acids, Acyclic; D007473:Ion Channels; D008293:Malates; D019343:Citric Acid; D007811:Lanthanum; C030298:malic acid; D019342:Acetic Acid