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 roo ts (Triticum aestivum L.). Neither hypoxia nor subsequent re-aeration cause d significant changes in SOD isoenzyme pattern compared with aerated contro ls. However, anoxia led to the appearance of additional activity bands of S OD in native gels resulting in an increase in total activity. Additional is oformic bands remained also apparent in the following recovery period. Re-a eration 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 dimi nished, protein content of different SOD isoforms increased with duration o f anoxia. Incubation of roots with cycloheximide revealed that the addition al activity bands and higher SOD protein content under anoxia were not due to de novo synthesis. Crude subcellular fractionation experiments implied t hat the anoxia-responsive SOD isoforms might be plastid-associated. We sugg est that SOD is a very stable enzyme which, under anoxia, accumulates relat ive to total protein content and remains active even after protein modifica tion under severe environmental stress conditions.