Copper uptake and translocation in chicory (Cichorium intybus L. cv Grasslands Puna) and tomato (Lycopersicon esculentum Mill. cv Rondy) plants grownin NFT system. II. The role of nicotianamine and histidine in xylem sap copper transport

The effect of rooting media Cu concentration (0.05-20 mg Cu L-1) on amino a cid concentrations and copper speciation in the xylem sap of chicory and to mato plants was measured using 6 week old plants grown in a nutrient film t echnique system (NFT). Irrespective of the Cu concentration in the nutrient solutions, more than 99.68% and 99.74% of total Cu in tomato and chicory x ylem sap was in a bound form. When exposed to high Cu concentrations in the rooting media, amino acid concentrations in the sap increased. Relative to other amino acids, the concentrations of glutamine (Gln), histidine (His), asparagine (Asn), valine (Val), nicotianamine (NA) and proline (Pro) in to mato xylem saps, and His, gamma-aminobutyric acid (Gaba), glutamic acid (Gl u), leucine (Leu), NA and phenylalanine (Phe) in chicory xylem saps showed the greatest increases. The data indicate that induced synthesis of some fr ee amino acids as a specific and proportional response to Cu treatment. For a single complexation amino acid, the solution Cu(2+)concentration vs pH t itration curve for NA at 0.06-0.07 mM was most similar, closely followed by His at 0.5-0.6 mM, to the solution Cu(2+)concentration behaviour in both t omato and chicory xylem sap. It is concluded that increased Cu concentratio ns in the rooting media induced selective synthesis of certain amino acid w hich include NA, His, Asn and Gln which have high stability constants with Cu. NA and His have the highest binding constants for Cu and the concentrat ions of NA and His in chicory and tomato xylem saps can account for all the bound Cu carried in the sap.