Effect of lead, nickel and vanadium contamination on organic acid transport in xylem sap of cucumber

Three organic acids (citric, fumaric and malic) of the Krebs cycle were measured by the reversed-phase high performance Liquid chromatography (RP-HPLC) technique in the xylem saps of cucumber plants grown in (i) control nutrient solutions containing iron as Fe(III)-ethylene-diamine-tetraacetate (Fe(III)-EDTA), Fe(III)-citrate or FeCl(3) and (ii) in nutrient solutions contaminated with nickel,lead or vanadium in a concentration of 10(-5) M. Simultaneously, the heavy metal content of the xylem sap samples was determined by total reflection X-ray fluorescence spectrometry (TXRF). In the presence of lead or nickel contamination the transport of the organic acids became higher by factor 1.1-2.3 compared to the control plants when Fe(III)-citrate or Fe(III)-chloride was added to the nutrient solutions. In the case of plants growing in Fe(III)-EDTA containing solutions, however, the transport of the organic acids decreased by 30-40%. The effect of vanadium on the transport of organic acids was considerably smaller. Generally, the deviation in the organic acid transport between the contaminated and the control plants was proportional to the heavy metal transport in the xylem in the sequence Ni > Pb > V. (C) 1999 Elsevier Science Inc. All rights reserved.