Archivio Journal of Plant Pathology

Abstract:

Protein synthesis and the activity of superoxide dismutases (SODs) were analyzed in bean plants (Phaseolus vulgaris L.) cv. ‘Groffy’ exposed to acute and chronic ozone (O3) fumigation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of total soluble leaf proteins revealed the accumulation of a newly synthesised 33 kDa polypeptide following acute (150 nl l-1) and chronic (50 nl l-1 and 100 nl l-1) treatments and the disappearance of a 36 kDa polypeptide after three hours of recovery from the acute treatment. The control plants showed four distinct SOD isoforms with a relative mobility (Rf) of 0.45 (MnSOD), 0.59 (Cu/ZnSOD), 0.80 (Cu/ZnSOD), and 0.85 (unidentified). Acute O3 fumigation induced a rise of MnSOD activity while the levels of both Cu/ZnSOD isoenzymes remained almost unaltered. However, the activity of the more anodic Cu/ZnSOD isoform increased remarkably after three hours of recovery in clean air. Two additional SOD isoenzymes (Rf = 0.63 and 0.68), induced by chronic fumigation, reached highest values in plants treated with 100 nl l-1 of O3 for seven days. Under chronic conditions, MnSOD activity levels remained unaltered or fell with respect to control plants. By contrast, a rise of the activities of both Cu/ZnSOD isoforms was observed after fumigation protracted for two or four days. Nevertheless, after seven days of treatment, levels of both Cu/ZnSOD isoenzymes and of the more anodic (Rf = 0.85) SOD isoform decreased. Changes in the levels of distinct components of the SOD system depending on the level of O3 fumigation imposed suggest a specific function for each isoform in protecting plant cells from oxidative stress.