title: Organic acids enhance the uptake of lead by wheat roots.
abstract: The uptake and bioavailability of lead (Pb) in soil-plant systems remain poorly understood. This study indicates that acetic and malic acids enhance the uptake of Pb by wheat (Triticum aestivum L.) roots under hydroponic conditions. The net concentration-dependent uptake influx of Pb in the presence and absence of organic acids was characterized by Michaelis-Menten type nonsaturating kinetic curves that could be resolved into linear and saturable components. Fitted maximum uptake rates (V (max)) of the Michaelis-Menton saturable component in the presence of acetic and malic acids were, respectively, 2.45 and 1.63 times those of the control, while the Michaelis-Menten K (m) values of 5.5, 3.7 and 2.2 microM, respectively, remained unchanged. Enhanced Pb uptake by organic acids was partially mediated by Ca(2+) and K(+) channels, and also depended upon the physiological function of the plasma membrane P-type ATPase. Uptake may have been further enhanced by an effectively thinner unstirred layer of Pb adjacent to the roots, leading to more rapid diffusion towards roots. X-ray absorption spectroscopic studies provided evidence that the coordination environment of Pb in wheat roots was similar to that of Pb(CH(3)COO)(2)x3H(2)O in that one Pb atom was coordinated to four oxygen atoms via the carboxylate group.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box 2871, Beijing, 100085, China.
authors.forename: Huanhua
authors.initials: H
authors.lastname: Wang
authors.forename: Xiaoquan
authors.initials: X
authors.lastname: Shan
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.forename: Yaning
authors.initials: Y
authors.lastname: Xie
authors.forename: Bei
authors.initials: B
authors.lastname: Wen
authors.forename: Shuzhen
authors.initials: S
authors.lastname: Zhang
authors.forename: Fang
authors.initials: F
authors.lastname: Han
authors.forename: Martinus Th
authors.initials: MT
authors.lastname: van Genuchten
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007854:Lead / Q000378:metabolism*; D008293:Malates / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D013997:Time Factors; D014908:Triticum / Q000187:drug effects / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D008293:Malates; D026902:Potassium Channel Blockers; D007854:Lead; D014638:Vanadates; C030298:malic acid; D019342:Acetic Acid