Antioxidant enzyme isoforms on gels in two poplar clones differing in sensitivity after exposure to ozone

The effect of acute ozone (O-3) fumigation on isozyme patterns of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) in mature (ML) and young leaves (YL) of two poplar clones, contrasting in O-3-sensitivity was analysed. Untreated leaves of both the O-3-sensitive (O-3-S) clone Eridano of Populus deltoides x P. maximowiczii and the O-3-resistant (O-3-R) clone I-214 of P. x euramericana showed four distinct SOD isoforms with a relative mobility (R-f) of 0.54 (MnSOD), 0.60 (Cu/ZnSOD), 0.65 (unidentified), and 0.71 (Cu/ZnSOD). After O-3-fumigation the activity of the SOD isoforms showed only quantitative variations with respect to control plants. In ML of untreated O-3-R plants seven POD isoforms (R-f = 0.13, 0.19, 0.34, 0.59, 0.64, 0.70 and 0.75) were found, while in YL one isoform (R-f = 0.34) was undetected. Only three POD isoforms in both ML and YL of untreated O-3-S plants were resolved. The electrophoretic pattern of POD in O-3-S leaves was greatly modified by acute O-3-fumigation with the appearance of new isoforms in both YL and ML and the disappearance of an isoform (R-f = 0.13) in YL. Additionally, O-3-exposure induced the appearance of two APX isoforms in YL (R-f = 0.66 and 0.70), and one isoform in ML (R-f = 0.70) of the O-3-S clone. By contrast, the activity of the three APX isoformes (R-f = 0.64, 0.70 and 0.76) detected in O-3-R leaves showed only quantitative variation with respect to untreated plants. From these data it is concluded that: 1) in these poplar hybrids antioxidant enzyme activity is developmentally regulated and greatly affected by acute O-3 stress treatments and 2) the different enzymes activity displayed by the two poplar clones, especially for POD and APX isoformes, could partly explain their distinct O-3-sensitivity.