Protein pattern and Fe-superoxide dismutase activity of bean plants under sulphur dioxide stress

Protein synthesis and superoxide dismutase (SODs) activities were analysed in bean plants (Phaseolus vulgaris L., cv. Groffy) exposed to sulphur dioxide (SO2) (30, 60 or 90 nl/l SO2). After long-term treatments (2, 4 or 7 days), sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of water-soluble leaf proteins revealed the appearance of new polypeptides corresponding to 34.5 and 31 kDa. Quantitative differences between control and treated plants were observed for subunits of 50, 47, 42, 32, 30 and 28 kDa. In SO2-fumigated plants, the activity patterns of four SOD-isoforms, with a relative mobility (R-f) of 0.45 (MnSOD), 0.59 (Cu/ZnSOD), 0.80 (Cu/ZnSOD) and 0.85 (not identified), showed only small quantitative variations in comparison with unexposed plants. In control leaves the FeSOD isoenzyme was not detected, whereas its activity pattern (R-f=0.50) increased to a detectable level always after 2 days of fumigation with 30 nl/l SO2. It is proposed that the rise of FeSOD activity represents the initial activation of the enzymatic antioxidant system to counteract the superoxide anion generated during the radical-initiated oxidation Of SO2 in illuminated chloroplasts.