Abstract: Two cultivars of Festuca rubra L., namely metal tolerant "Merlin" and metal sensitive "S59", were treated with culture media containing Cd2 + at various concentrations ranging from 0 to 2.5 mmol/L. The biomass of the grass seedlings of both cuhivars was significantly dropped in connection to increase in metal concentration and treatmental time. The degree of inhibition by 0.5 mmol/L Cd2+ in "Merlin" was quite similar to that caused by 0.25 mmol/L Cd2+ in "S59" ,indicating that "Merlin" was relatively resistant to metal stress. Accompanying with the inhibition of growth by Cd2 + , malonyl dialdehyde (MDA) content and peroxidase (POD) activity measured in the seedlings increased drastically, while the activities of catalase (CAT) and superoxide dismutase (SOD) decreased with significant drop in total protein content. The remarkable enhancement of MDA in the grass seedlings appeared to be an obvious physiological response due to Cd2 + treatment. When plants treated with 2.5 mmol/L Cd2+ for 6 days,MDA increased by 109% and 143% in "Merlin" and "S59", respectively. There was a close positive correlation between MDA content and Cd2 + concentration, and a negative correlation between MDA and plant growth. As slight decrease in SOD activity was found accompanied by a drastic elevation of MDA content. This observation may imply that free radical and MDA may play an important role in the Cd2 + led toxicity in plants.

Key words: Pollution by metals, Cadmium toxicity, Free radicals, SOD, malonyl dialdehyde