Chemical forms of aluminum in xylem sap of tea plants (Camellia sinensis L.) Akio Morita a, * , Hideki Horie b , Yousuke Fujii a , Satoshi Takatsu a , Naoharu Watanabe a , Akihito Yagi a , Hiromi Yokota a a Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan b National Institute of Vegetable and Tea Science, 360 Kusao, Ano-cho, Aki-gun, Mie 514-2392, Japan Received in revised form 14 June 2004 Available online 23 September 2004 Abstract To identify the chemical forms of aluminum (Al) transported from roots to shoots of tea plants (C. sinensis L.), 27 Al-nuclear magnetic resonance and 19 F NMR spectroscopy were used to analyze xylem sap. The concentration of Al in collected xylem sap was 0.29 mM, twice as high as that of F. Catechins were not detected in x The concentration of malic acid in xylem sap was higher than that of citric acid, whereas the concentration of oxalic acid was negligible. There were two signals in the 27 Al NMR spectra of xylem sap, a larger signal at 11 ppm and a smaller one at 1.5 ppm. The former signal was consistent with the peak for an Al–citrate model solution,suggesting that an Al–citrate complex was present in xylem sap. Although the latter signal at 1.5 ppm was thought to indicate the presence of an Al–F complex (at 1.7 ppm) i sap, there was only one signal at 122 ppm in the 19 F NMR spectrum of xylem sap, indicating that the main F complex in xylem sap was F . These results indicate that Al might be translocated as a complex with citrate, while Al–malate, Al–oxalate and Al–F com are not major Al complexes in xylem sap of tea plants. 2004 Elsevier Ltd. All rights reserved. Keywords: Camellia sinensis; Theaceac; Aluminum; Citric acid; Malic acid; 27 Al NMR; 19 F NMR 1. Introduction Al is one of the most abundant elements in the earthÕs crust and comprises 7% of it. Under acidic conditions (pH < 5.0), Al is solubilized into a toxic trivalent cation, Al 3+ (Foy et al.,1978;Taylor,1991).In many agricul- turally importantplant species, the presence of only micromolar concentrations of Al 3+ can result in the inhi- bition of root growth within minutes or hours ( Kochian, 1995). Thus, Al toxicity has been recognized as a major factor that limits plant growth in acidic soil. On the other hand, some plant species, known as ‘‘Al accumulators’’, accumulate Al at high concentrations in the aerial parts of the plants without showing symptoms of Al toxicity.The tea plant (Camellia sinensis L.) is a well-known Al-accumulating plant that grows wellin strongly acidic soils that contain high levels of soluble Al. The tea plant takes up Al throughout its life (Che- nery, 1955), and old leaves contain up to 30,000 mg kg 1 of Al on a dry weight basis (Matsumoto et al., 1976). These findings suggest that detoxification of Al occurs in tea plants.Elucidation of the mechanism ofthis 0031-9422/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.phytochem.2004.08.043 * Corresponding author. Tel./fax: +81 54 238 4591. E-mail address: aamorit@agr.shizuoka.ac.jp (A. Morita). www.elsevier.com/locate/phytochem Phytochemistry 65 (2004) 2775–2780 PHYTOCHEMISTRY