HIGH ALUMINUM RESISTANCE IN BUCKWHEAT - II - OXALIC-ACID DETOXIFIES ALUMINUM INTERNALLY

which Buckwheat (Fagopyrum esculentum Moench. cv Jianxi): shows high A l resistance, accumulates Al in the leaves. The Internal detoxificatio n mechanism was studied by purifying and identifying Al complexes in t he leaves and roofs. About 90% of Al accumulated in the leaves was fou nd in the cell sap, in which the dominant organic acid was oxalic acid . Purification of the Al complex in the cell sap of leaves by molecula r-sieve chromatography resulted in a complex with a ratio of Al to oxa lic acid of 1:3. A C-13-nuclear magnetic resonance study of the purifi ed cell sap revealed only one signal at a chemical shift 164.4 ppm, wh ich was assigned to the Al-chelated carboxylic group of oxalic acid. A Al-27-nuclear magnetic resonance analysis revealed one major signal a t the chemical shift of 16.0 to 17.0 ppm, with a minor signal at the c hemical shift of 11.0 to 12 ppm in both the intact roots and their cel l sap, which is consistent with the Al-oxalate complexes at 1:3 and 2: 2 ratios, respectively. The purified cell sap was not phytotoxic to ro ot elongation in corn (Zea mays). All of these results indicate that A l tolerance in the roots and leaves of buckwheat is achieved by the fo rmation of a nonphytotoxic Al-oxalate (1:3) complex.