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 applied for 12 h with 100 mmol/L mannitol; the wilting state (85% of the original 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. Wilted and osmotically stressed roots exhibited a lack of stress-inducible antioxidative enzymes and a decrease in glutathione and ascorbate contents with the duration of treatments. An enhanced capability to dismutate superoxide was observed in wilted leaves and in osmotically stressed old leaves; ascorbate peroxidase activity was solely enhanced in wilted leaves, but ascorbate content remained stable both in the case of desiccated and osmotically stressed leaves. Although glutathione reductase activity decreased in wilted and mannitol-treated leaves, glutathione content remained also stable in stressed leaves. After rehydration of 12-h wilted leaves and roots, no recovery of the initial rate of each enzyme activity was observed. The adaptive response of roots and leaves of poplar to oxidative stress generated by wilting and osmotic stress was discussed.