Differential Stimulation of Ascorbate Peroxidase Isoforms by Ozone Exposure in Sunflower Plants

In sunflower plants exposed to 150 nl L-I of 0 3 (4 h day-I for 4 days) an enhancement in the activity of APx was found at both the apoplastic and symplastic levels, while stromal and thylakoid-bound chloroplastic APx activity did not change. PAGE analysis confirmed the presence ofAPx activity in the apoplast and revealed different APx isoenzyme patterns between control and 03-treated plants in either apoplastic and cytoplasmic samples. Immunoreaction with a cytosolic APx antibody revealed, at both the apoplastic and symplastic levels, only one band, more evident in the 03-treated than in the control plants. These results support the hypothesis of a cytoplasmic origin for the apoplastic isoform. Thus, sunflower plants seem to adapt to 03-induced oxidative stress through the induction of genes coding for APx proteins whose enzymatic activity enhancement at the apoplastic and cytosolic levels may act as a biochemical defence line against owne pollution damage.