INFLUENCE OF HEAVY METALS ON N-METABOLISM, STRESS-RELATED BIOMARKERS AND PRODUCT QUALITY IN FOOD PLANTS

H. Bergmann*, B. Machelett, B. Lippmann (Institute of Nutrition Science, University of Jena, Dornburger Str. 25, D-07743 Jena, Germany, Telephone: (00493641) 949700, Fax: (00493641)949702

Unfavourable environments, such as drought or soil salinity, increase the pool of free amino acids (Protein-related and non-protein amino acids). Furthermore cadmium (Cd) promotes the formation of polyamines in plants.

Therefore in this contribution the influence of various heavy metals (Cd, Pb, Cu, Ni, Zn) and their ratios on the formation and contents of free amino acids and polyamines were examined in vegetables and cereal plants.

The release of amino acids from roots of maize rose in a hydroponic cukture, which was enriched with 2 ppm of water-soluble Cd. Thus, the exudation of the non-protein amino acids ß-alanine and aminobutyric acid increased significantly (about 150 %). Additionally, a threefold higher release of the stress indicator proline and a twofold higher exudation of the polyamine-precursor arginine were obtained.

In contaminated sandy soils the bioavailable Cd (1.5 ... 3 ppm) caused higher contents of trimethylglycine (glycine betaine) and trigonellin in barley (up to 50 %). Soil salinity enhanced the uptake of Cd and other heavy metals (Cu, Ni, Zn, Pb) and these unfavourable soil conditions resulted in a 4- to 8-fold increase of non-protein amino acids such as trimethylglycine formed from free serine (serine ( 2-aminoethanol ( choline (trimethylglycine).

In experiments with spinach an enrichment of a sandy soil with Cd (1.2 ppm) caused an tenfold higher Cd-content in leaves followed by an increased spermine concentration (up to 50 %). And, a contamination of soils and bean plants with nickel induced the formation of putrescine (up to 50 %; arginine is a precursor). The effects of soil pollution with heavy metals on the food quality are discussed.