Response of antioxidant enzymes to transfer from elevated carbon dioxide to air and ozone fumigation, in the leaves and roots of wild-type and a catalase-deficient mutant of barley

A catalase-deficient mutant (RPr 79/4) and the wild-type (cv. Maris Mink) barley (Hordeum vu/gare L.) counterpart, were grown for 3 weeks in high CO 2 (0.7%) and then transferred to air and ozone (120 nl 1 -1 ) in the light and shade for a period of 4 days. Leaves and roots were analysed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) activities. CAT activity in the leaves of the RPr 79/4 catalase-deficient mutant was around 5 -10% of that determined in Maris Mink, but in the roots, both genotypes contained approximately the same levels of activity. CAT activity in Maris Mink increased in the leaves after transferring plants from 0.7% CO 2 to air or ozone, reaching a maximum of 5-fold, after 4 days in shade and ozone. For the catalase-deficient mutant, only small increases in CAT activity were observed in light/air and light/ ozone treatments. In the roots, CAT activity decreased consistently in both genotypes, after plants were transferred from 0.7% CO 2 . The total soluble SOD activity in the leaves and roots of both genotypes increased after plants were transferred from 0.7% CO 2 . The analysis of SOD isolated from leaves following non-denaturing PAGE, revealed the presence of up to eight SOD isoenzymes classified as Mn-SOD or Cu/Zn-SODs; Fe-SOD was not detected. Significant changes in Mn- and Cu/Zn-SOD isoenzymes were observed; however, they could not account for the increase in total SOD activity. In leaves, GR activity also increased in Maris Mink and RPr 79/4, following transfer from 0.7% CO 2 : however, no constant pattern could be established, while in roots, GR activity was reduced after 4 days of the treatments. The data suggest that elevated CO 2 decreases oxidative stress in barley leaves and that soluble CAT and SOD activities increased rapidly after plants were transferred from elevated CO 2 , irrespective of the treatment (light, shade, air or ozone).