Expression and activity of isoenzymes of superoxide dismutase in wheat roots in response to hypoxia and anoxia

We investigated the effects of hypoxia, anoxia and reaeration on enzymatic activity and expression of superoxide dismutase (SOD) isoforms in wheat roots (Triticum aestivum L.). Neither hypoxia nor subsequent re-aeration caused significant changes in SOD isoenzyme pattern compared with aerated controls. However, anoxia led to the appearance of additional activity bands of SOD in native gels resulting in an increase in total activity. Additional isoformic bands remained also apparent in the following recovery period. Re-aeration following both hypoxia and anoxia resulted in an increased content of hydrogen peroxide in roots. SOD transcript and protein levels were only slightly altered in response to hypoxia. Although SOD mRNA levels were diminished, protein content of different SOD isoforms increased with duration of anoxia. Incubation of roots with cycloheximide revealed that the additional activity bands and higher SOD protein content under anoxia were not due to de novo synthesis. Crude subcellular fractionation experiments implied that the anoxia-responsive SOD isoforms might be plastid-associated. We suggest that SOD is a very stable enzyme which, under anoxia, accumulates relative to total protein content and remains active even after protein modification under severe environmental stress conditions.