The free oxygen radical scavenging enzymes and redox status in roots and leaves of Populus x Euramericana in response to osmotic stress, desiccation and rehydration

The redox status (ascorbate, glutathione under reduced and oxidized forms) and the activities of antioxidative enzymes (superoxide dismutase, catalase , ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase) were measured in leaves and roots of Populus euramericana cv. Luisa Avanzo cuttings exposed to wilting or to osmotic stress. Osmotic stress was applie d for 12 h with 100 mmol/L mannitol; the wilting state (85 % of the origina l fresh weight), which was reached in 15 min in roots, 75 min in old leaves and 145 min in young leaves, was maintained for 12 h. Superoxide synthesis was drastically enhanced in wilted organs vs. osmotically stressed ones. W ilted and osmotically stressed roots exhibited a lack of stress-inducible a ntioxidative enzymes and a decrease in glutathione and ascorbate contents w ith the duration of treatments. An enhanced capability to dismutate superox ide was observed in wilted leaves and in osmotically stressed old leaves; a scorbate peroxidase activity was solely enhanced in wilted leaves, but asco rbate content remained stable both in the case of desiccated and osmoticall y stressed leaves. Although glutathione reductase activity decreased in wil ted and mannitol-treated leaves, glutathione content remained also stable i n stressed leaves. After rehydration of 12-h wilted leaves and roots, no re covery of the initial rate of each enzyme activity was observed. The adapti ve response of roots and leaves of poplar to oxidative stress generated by wilting and osmotic stress was discussed.