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 dioxi de (SO2) (30, 60 or 90 nl/l SO2). After long-term treatments (2, 4 or 7 day s), sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) o f water-soluble leaf proteins revealed the appearance of new polypeptides c orresponding to 34.5 and 31 kDa. Quantitative differences between control a nd treated plants were observed for subunits of 50, 47, 42, 32, 30 and 28 k Da. In SO2-fumigated plants, the activity patterns of four SOD-isoforms, wi th a relative mobility (R-f) of 0.45 (MnSOD), 0.59 (Cu/ZnSOD), 0.80 (Cu/ZnS OD) and 0.85 (not identified), showed only small quantitative variations in comparison with unexposed plants. In control leaves the FeSOD isoenzyme wa s not detected, whereas its activity pattern (R-f=0.50) increased to a dete ctable level always after 2 days of fumigation with 30 nl/l SO2. It is prop osed that the rise of FeSOD activity represents the initial activation of t he enzymatic antioxidant system to counteract the superoxide anion generate d during the radical-initiated oxidation Of SO2 in illuminated chloroplasts .