DETERMINATION OF ORGANIC-ACIDS IN XYLEM SAP OF CUCUMBER - EFFECT OF LEAD CONTAMINATION

Lead, iron, and organic acid concentrations were determined in low-vol ume xylem sap samples of cucumbers grown in both ''lead-free'' and lea d-contaminated nutrient solutions containing either Fe-citrate or Fe-E DTA by total reflection X-ray fluorescence spectrometry (iron and lead ), graphite furnace atomic absorption spectrometry (lead), and reverse d-phase high-performance liquid chromatography (organic acids). Three acids of the Krebs cycle-citric, fumaric, and malic acids-were detecte d and measured. In presence of Fe-citrate the lead contamination resul ts in about three times higher organic acid production in the cucumber compared with the uncontaminated plants. At the same time the amount of transported iron decreases with about 20%. In presence of Fe-EDTA, the same amount of lead leads to a small change in organic acid produc tion; however, the uptake and the transport processes of iron are cons iderably hindered (similar to 35%). Lead transport in the xylem channe l was more than one order of magnitude higher when iron was added to t he nutrient solution as citrate instead of EDTA complex. These phenome na can be attributed to the participation of the organic acids in the translocation processes of the metals investigated. (C) 1998 Academic Press.