Editing Superoxide dismutase (section)

=== Plants ===

In [[higher plants]], superoxide dismutase enzymes (SODs) act as antioxidants and protect cellular components from being oxidized by [[reactive oxygen species]] (ROS).<ref name="Alscher">{{cite journal | vauthors = Alscher RG, Erturk N, Heath LS | title = Role of superoxide dismutases (SODs) in controlling oxidative stress in plants | journal = Journal of Experimental Botany | volume = 53 | issue = 372 | pages = 1331–1341 | date = May 2002 | pmid = 11997379 | doi = 10.1093/jexbot/53.372.1331 | doi-access = free }}</ref> ROS can form as a result of drought, injury, herbicides and pesticides, ozone, plant metabolic activity, nutrient deficiencies, photoinhibition, temperature above and below ground, toxic metals, and UV or gamma rays.<ref name="Smirnoff">{{cite journal | vauthors = Smirnoff N | title = The role of active oxygen in the response of plants to water deficit and desiccation | journal = The New Phytologist | volume = 125 | issue = 1 | pages = 27–58 | date = September 1993 | pmid = 33874604 | doi = 10.1111/j.1469-8137.1993.tb03863.x | doi-access = free | bibcode = 1993NewPh.125...27S }}</ref><ref name="Raychaudhuri">{{cite journal | vauthors = Raychaudhuri SS, Deng XW | title = The Role of Superoxide Dismutase in Combating Oxidative Stress in Higher Plants | journal = The Botanical Review | volume = 66 | issue = 1| pages = 89–98 | year = 2008 | doi = 10.1007/BF02857783 | s2cid = 7663001 }}</ref> To be specific, molecular O<sub>2</sub> is reduced to {{chem|O|2|-}} (a ROS called superoxide) when it absorbs an excited electron released from compounds of the electron transport chain. Superoxide is known to denature enzymes, oxidize lipids, and fragment DNA.<ref name="Smirnoff"/> SODs catalyze the production of O<sub>2</sub> and {{chem|H|2|O|2}} from superoxide ({{chem|O|2|-}}), which results in less harmful reactants.

When acclimating to increased levels of oxidative stress, SOD concentrations typically increase with the degree of stress conditions. The compartmentalization of different forms of SOD throughout the plant makes them counteract stress very effectively. There are three well-known and -studied classes of SOD metallic coenzymes that exist in plants. First, Fe SODs consist of two species, one homodimer (containing 1–2 g Fe) and one tetramer (containing 2–4 g Fe). They are thought to be the most ancient SOD metalloenzymes and are found within both prokaryotes and eukaryotes. Fe SODs are most abundantly localized inside plant chloroplasts, where they are indigenous. Second, Mn SODs consist of a homodimer and homotetramer species each containing a single Mn(III) atom per subunit. They are found predominantly in mitochondrion and peroxisomes. Third, Cu-Zn SODs have electrical properties very different from those of the other two classes. These are concentrated in the [[chloroplast]], [[cytosol]], and in some cases the extracellular space. Note that Cu-Zn SODs provide less protection than Fe SODs when localized in the chloroplast.<ref name="Alscher"/><ref name="Smirnoff"/><ref name="Raychaudhuri"/>