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Approaches to Enhance Antioxidant Defense in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Hamid Mohammadi, Saeid Hazrati, Mohsen Janmohammadi
Fat-soluble antioxidants (vitamin E, carotenoids) and antioxidant enzymes bonded with cell membranes in higher plants are known as the first defensive molecules against reactive oxygen species produced in the cell membrane, while water-soluble antioxidants (vitamin C) eliminate ROS in aquatic phases. The balance between superoxide dismutase and ascorbate peroxidase or catalase in cells is crucial in determining the level of superoxide and hydrogen peroxide radicals. The most important pathways for removing the ROS in plants include superoxide dismutase found in most cell organs, water–water cycle in chloroplasts, glutathione–ascorbate cycles in the cytosol, mitochondria, apoplast, peroxisomes, glutathione peroxidase, and catalase in peroxisomes. The glutathione–ascorbate cycle takes place in most cell parts and plays a central role in controlling the level of reactive oxygen species. Catalase is only found in peroxisomes and acts as detoxifier during stress. Therefore, higher amounts of antioxidant compounds play an important role in protecting plants cells against oxidative stresses (Noctor and Foyer, 1998).
Antioxidant response mechanism of freshwater microalgae species to reactive oxygen species production: a mini review
Published in Chemistry and Ecology, 2020
Adamu Yunusa Ugya, Tijjani Sabiu Imam, Anfeng Li, Jincai Ma, Xiuyi Hua
A non-enzymatic antioxidant produced by freshwater microalgae include ascorbic acid, tocopherol, carotenoids, flavonoids, hydroquinone, phycocyanin, proline, reduce glutathione, polyamine as summarised in Table 2 for some specific microalgae species in different experimental conditions [131]. This kind of antioxidant interact with various freshwater microalgae cell parts and also play a vital role as enzyme co-factor and in freshwater microalgae defense mechanism thereby influencing plants growth and development. They protect freshwater microalgaecells from ROS by interrupting free radical chain reaction [132]. Tocopherol helps freshwater microalgae cell to scavenge excess ROS by donating a hydrogen atom to ROS. This is because at 323 KJ/mol the O-H bond in tocopherol is weak if compared to the O-H bond in other organic compounds such as phenol etc. Tocopherol readily donates a hydrogen atom to ROS leading to the formation of tocopheryl radical which is unreactive but accept hydrogen to become tocopherol which is stored in the freshwater microalgae cell membrane [133,134]. Carotenoid is a compound with a polyene chain structure consisting of 9–11 double bonds terminating in a ring. The conjugated double bond of carotenoid is advantageous for the annulling of the adverse effect of ROS since the double conjugated double bonds leads to the transfer of an electron from carotenoids to ROS during the triplet–triplet transfer [135,136]. Phycocyanin has been shown by [137–139] to scavenge ROS, including peroxyl, hydroxyl, and alkoxyl radicals, thereby preventing lipid peroxidation. Ascorbic acid and reduced glutathione are important components of the glutathione-ascorbate cycle which is a metabolic process of detoxifying ROS particularly H2O2 [140]. The pathway involves the reduction of H2O2 to water by ascorbate peroxidase with ascorbate serving as an electron donor [141]. The oxidised ascorbate then accepts hydrogen from monodehydroascorbate reductase to form ascorbate [141]. Monodehydroascorbate is an unstable radical as such dissociate to form ascorbate and dehydroascorbate, and dehydroascorbate is reduced by glutathione leading to the formation of ascorbate and reduced glutathione. NADPH then reduces the oxidised glutathione into glutathione so that both ascorbate and glutathione are not consumed [142]. Flavonoid is metabolites that are biosynthesized in the endoplasmatic reticulum and chloroplast of some freshwater microalgae cells. Flavonoid inhibits the generation of ROS by the formation of complexes with Cu2+ and Fe3+[143].