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| Components | Location | Function |
|
| Enzymatic antioxidants | | |
| Superoxide dismutase (SOD) | | Dismutation of : + + 2H+ → 2H2O2 + O2 |
| Cu, Zn-SOD | Cytosol, plastids |
| Mn-SOD | Mitochondria, bacteroides |
| Fe-SOD | Plastids, some bacteroides |
| Catalase | Peroxisomes, bacteroides | Dismutation of H2O2: 2H2O2 → 2H2O + O2 |
| Guaiacol peroxidase (GPX) | Plasma membrane, vacuoles | Detoxification of H2O2: H2O2 + → H2O + |
| Peroxiredoxins | Cytosol, mitochondria | Reduction of H2O2 or alkyl hydroperoxides (ROOH) to H2O or respective alcohols (ROH): ROOH + Trx-(SH)2 → ROH → Trx-S2 + H2O |
| Enzymes of ascorbate-glutathione cycle (AA-GSH cycle) | | |
Cytosol (mainly), mitochondria, plastids,
peroxisomes | Detoxification of H2O2 in a series of reactions |
| Ascorbate peroxidase (APX) | APX: H2O2 + AA → 2H2O + MDHA (DHA) |
| Monodehydroascorbate reductase (MR) | MR: 2MDHA + NADH → 2AA + NAD |
| Dehydroascorbate reductase (DR) | DR: DHA + 2GSH → AA + GSSG |
| Glutathione reductase (GR) | GR: GSSG + NADPH → 2GSH + NADP+ |
| Enzymes of GSH metabolism | | |
| Glutathione peroxidase (GSH-PX) | Cytosol, plastids, bacteroides | Detoxification of H2O2: H2O2 + GSH → 2H2O + GSSG |
| Glutathione reductase (GR) | Cytosol, mitochondria, plastids, bacteroides | Regeneration of oxidized glutathione: GSSG + NADPH → 2GSH + NADP+ |
| α-Glutamylcysteine synthetase and glutathione synthetase | Cytosol, plastids, bacteroides | GSH synthesis de novo |
| Glutathione-S-transferase | Cytosol (mainly), plastids mitochondria, bacteroides | Detoxification of xenobiotics via conjugation with GSH |
|
| Nonenzymatic antioxidants | | |
| Ascorbic acid (AA) | Cytosol, mitochondria, plastids,
peroxisomes | Direct scavenging of ROS, a substrate for APX |
| Glutathione (GSH) | Cytosol, mitochondria, plastids, bacteroides | Direct scavenging of ROS, a cosubstrate for DR, GSH-PX, and glutathione-S-transferases |
| α-Tocopherol | Plastids | Direct scavenging of ROS, quenching of lipid radicals in membranes |
| Carotenoids | Plastids | Quenching of electron-excited molecules, protection of chlorophylls from photodamage |
| Phenol compounds (phenolic acids, flavonoids, etc.) | Vacuoles (mainly), cytosol, plastids, cell wall | Direct scavenging of ROS and lipid radicals, metal-chelating activity |
| Ferritin, phytochelatins, and metallothioneins | Plastids, vacuoles, cytosol | Metal-binding activity |
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