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. Gro€y) exposed to sulphur dioxide (SO2) (30, 60 or 90 nl/l SO2). After long-term treatments (2, 4 or 7 days), sodium dodecyl sulphate-polyacryla- mide gel electrophoresis (SDS-PAGE) of water-soluble leaf proteins revealed the appearance of new polypep- tides corresponding to 34.5 and 31 kDa. Quantitative di€erences 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 (Rf) of 0.45 (MnSOD), 0.59 (Cu/ZnSOD), 0.80 (Cu/ZnSOD) and 0.85 (not identi®ed), showed only small quantitative variations in comparison with unexposed plants. In control leaves the FeSOD isoenzyme was not detected, whereas its activity pattern (Rfˆ0.50) 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.