Description:
<jats:p>Mature <jats:italic>Pinus sylvestris</jats:italic> trees were exposed to air‐pollution strees in an open field fumigation experiment. The trees were exposed to low‐levels of sulphur dioxide and nitrogen oxides throughout the whole growing season (June to October 1991). Three age‐classes (current, one‐ and two‐year‐old) of needles were collected from exposed and control trees and the expression of chloroplastic and cytosolic CuZn‐superoxide dismutase (SOD; EC 1.15.1.1) genes was studied. The levels of chloroplastic and cytosolic CuZn‐SOD mRNA were significantly (up to 2.3‐fold) higher in exposed trees for all age‐classes of needles as compared to control trees. No significant differences were observed between different needle age‐classes in CuZn‐SOD mRNA induction. The chloroplastic and cytosolic CuZn‐SOD mRNA were induced to the same extent, however, the level of chloroplastic CuZn‐SOD mRNA was higher than the cytosolic one. Small differences were observed in CuZn‐SOD mRNA levels for individual trees both within exposed and control areas. Protein activity measurements of the CuZn‐SOD isozymes did not reveal any significant differences between control and exposed trees. The results are discussed in relation to protection against oxidant stress from air pollutants.</jats:p>