COPPER TOXICITY IN YOUNG MAIZE (ZEA-MAYS L) PLANTS - EFFECTS ON GROWTH, MINERAL AND CHLOROPHYLL CONTENTS, AND ENZYME-ACTIVITIES

Changes in the growth parameters and in enzyme activities were studied in roots and leaves of 14-days old maize grown in a nutrient solution containing various copper concentrations (i.e. 0.01 to 10 mu M). A si gnificant decrease in root and leaf biomass was only found at 10 mu M Cu. In contrast, changes in several enzyme activities occured at lower copper concentrations in the solution, corresponding to different thr eshold values which are lower than those observed for growth parameter s. Peroxidase (POD) activity significantly increased in all investigat ed plant organs (i.e. 3rd-leaf, 4th-leaf and roots) in relation to the ir copper content. Additionally, glucose-6-phosphate dehydrogenase (G- 6-PDH), and isocitrate dehydrogenase (ICDH) activities decreased in th e leaves, especially in the 4th-leaf. However, the activity of malic e nzyme (ME), G-6-PDH, glutamate dehydrogenase (GDH) and ICDH increased with the copper content in roots. According to the relationship betwee n POD activity and copper content, the toxic critical value was set at 26 mg Cu per kg dry matter (DM) in roots and 21 mg Cu per kg DM in th e 3rd-leaf. In roots, a new isoenzyme of peroxidase appeared for coppe r content above 12.6 mg Cu kg DM(-1). Measurement of enzyme activity, especially that of POD and Cu-specific changes in the (iso)peroxidase pattern, might be used as biomarkers to assess the phytotoxicity for m aize grown on copper-contaminated substrata.