The chemical behaviour of heavy metals plays a prominent role in the induction of oxidative stress.

It is often described that different environmental stress factors stimulate the production of reactive oxygen species and increase the activity of several enzymes quenching these radicals. The ascorbate-glutathione pathway is also involved in plant defence against oxidative stress. Therefore the effects of 2 metals (Cu, Zn) with different chemical behaviour were investigated on the enzymes of this pathway in the primary leaves of bean seedlings grown on hydroponics and supplied with a 50 microM concentration of both metals. The results obtained demonstrate that the capacities of the enzymes involved in the ascorbate-glutathione pathway increase after metal application, indicating that they induce oxidative stress indeed. However striking differences in the relative induction time of these enzymes suggest that the chemical behaviour of the metals applied, plays an important role in the induction of oxidative stress as well as in the defence mechanism against it.