Superoxide dismutase, catalase and nitrogenase activities of symbiotic Frankia (Alnus incana) in response to different oxygen tensions

Abstract

Presence and activity of the enzymes superoxide dismutase (SOD) and catalase were studied in Frankia in symbiosis with Alnus incana (L.) Moench. Analysis on native PAGE gels indicated that symbiotic Frankia contained an FeSOD and catalase. The activity of the enzymes was in the same range as reported for cultured Frankia. Attempts to characterize SOD by western blots with antisera from Escherichia coli and Azotobacter vinelandii did not give clear‐cut results with the antibodies used. Alnus incana plants were grown with the root system in 5, 10, 21 or 40% O2 for up to 6 days. Nitrogenase activity, measured as ARA (acetylene reducing activity) dropped within 3 h when roots were exposed to low or high oxygen. At 40% O2 ARA was almost completely lost while at 5 and 10% O2 ARA decreased to 69 and 74% of the inital value, respectively, Nitrogenase activity recovered at ail oxygen tensions. Recovery rates resembled the continuous increase in ARA in plants continuosly kept at 21% O2, and suggests that new vesicles with envelopes of appropriate thickness were formed. The ARA measurements confirm results from an earlier study where nitrogenase activity was measured as H2 evolution. There was a tendency for increased SOD and catalase activities in Frankia from root systems exposed to 40% O2 for 24 h but not earlier or later than this. When data from all experimental times were pooled. SOD activity increased significantly with increased oxygen tension whereas catalase activity decreased. Although ARA per plant varied with oxygen tension, there was no statistically significant correlation between ARA and SOD or between ARA and catalase. It seems that being linked to nitrogenase activity is only one role of SOD and catalase in this symbiotic Frankia.