Role of Superoxide Dismutases (SODs) in Controlling Oxidative Stress in Plants

Reactive O2 species (ROS) are produced in both stressed and unstressed cells. Plants have well developed defence systems against ROS, involving both limiting the formation of ROS as well as instituting its removal. Under unstressed conditions, the formation and removal of O2 are in balance. However, the defence system, when presented with increased ROS formation under stress conditions, can be overwhelmed. Within a cell, the superoxide dismutases (SODs) constitute the first line of defence against ROS. Specialization of function among the SODs may be due to a combination of the influence of subcellular location of enzyme and upstream sequences in the genomic sequence. The commonality of elements in the upstream sequences of Fe, Mn, and Cu/Zn SODs suggest a relatively recent origin for those regulatory regions. These differences in the upstream regions of the three FeSOD genes suggest differing regulatory control which is borne out in the research literature. The finding that the upstream sequences of Mn and the peroxisomal Cu/Zn SODs have three common elements suggests a common regulatory pathway. The tools available to dissect further the molecular basis for antioxidant defence responses in plant cells. SODs are clearly among the most important of those defences, when coupled with the necessary downstream events for full detoxification of ROS.

Ruth Grene Alscher, Neval Ertuk, and Lenwood S. Heath (Journal of Experimental Botany, May 2002)