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Microalgal Metal Remediation from Industrial Wastewater
Published in Shashi Kant Bhatia, Sanjeet Mehariya, Obulisamy Parthiba Karthikeyan, Algal Biorefineries and the Circular Bioeconomy, 2022
Anna Aksmann, Wojciech Pokora, Agnieszka Baścik-Remisiewicz, Martyna Zalewska
Because the ascorbate-GSH cycle takes place in almost all cell compartments, it is suggested that the enzymes that catalyze this cycle's reactions play key roles in controlling intracellular levels of ROS, especially hydrogen peroxide, known as the intracellular signaling molecule and activator of the antioxidant defense system (Nazir et al., 2020). The majority of H2O2 generated in the cell is scavenged by peroxisomal and glyoxysomal CAT (Li and Ma, 2021). However, a wide range of peroxidases that have high affinity for H2O2 and are present in other cell compartments play significant roles in degradation of H2O2 that is unavailable to CAT (Caverzan et al., 2019). Ascorbate peroxidase is localized in the cytosol of algal cells and mainly in chloroplasts, where the soluble form is found in stroma; in the thylakoid membrane, APX is a transmembrane protein (Caverzan et al., 2019). The reduction of H2O2 to water is catalyzed by APX, with simultaneous transformation of monodihydroascorbate to ascorbate. The recovery of ascorbate to its reduced form is catalyzed by monodihydroascorbate reductase.
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
The glutathione–ascorbate cycle is another mechanism that reduces the excess energy by NADPH. This cycle is found in all of the plant cell components, and, in addition, the high affinity of ascorbate peroxidase (APX) for H2O2 indicates its crucial role in controlling ROS. Antioxidants, such as ascorbic acid and glutathione, found in high concentrations in chloroplasts and other cellular components, are very important in the plant’s defense mechanisms during oxidative stress (Noctor and Foyer, 1998). Therefore, maintaining high ratios of reduced ascorbate and glutathione in cells is essential for appropriate ROS scavenging, and this ratio is retained by GR. MDAR and dehydroascorbate reductase (DHAR) use the NADPH as a reducing agent (Asada, 1999). According to the study of Mohammadi and Moradi (2016) on wheat cultivars under water stress, APX enzyme activity was increased under water stress. Research shows that components of this cycle act either directly through scavenging or indirectly through the activation of defense mechanisms. Glutathione and ascorbate play an important role in the maintenance of cellular redox homeostasis. Besides, the high levels of the reduced form of these two compounds play an important role in activating the defense mechanisms of plants during stress conditions. In addition, glutathione has several roles, including the detoxifying of heavy metals, the transport and storage of sulfur, the regulation of the expression of the gene associated with defense, and protein activity, while ascorbic acid acts as a signal-transfer molecule, the cofactor of some enzymes, and the photoprotection mechanism in the xanthophyll cycle. Increasing the expression of APX genes in several abiotic stresses (Rosa et al., 2010; Caverzan et al., 2014), GPX in wheat plants during salinity stress, H2O2, and treatment with ABA (Zhai et al., 2013) were identified.
The beneficial role of potassium in Cd-induced stress alleviation and growth improvement in Gladiolus grandiflora L.
Published in International Journal of Phytoremediation, 2018
Nasim Ahmad Yasin, Malik Muhammad Zaheer, Waheed Ullah Khan, Sajid Rashid Ahmad, Aqeel Ahmad, Aamir Ali, Waheed Akram
The antioxidant enzymes including SOD, CAT, POD, and APX play a vital role in alleviation of oxidative stress in plants (Ahmad et al. 2015). During current study, the activities of antioxidant enzymes including APX, SOD, POD, and CAT, increased under low concentration of Cd stress which further increased by supplementation of K in plants under stress (Figure 2). Our results reveal that improved activity of antioxidant enzymes helped plants to survive Cd stress. Current data also revealed that K may induce further activity of these enzymes under stress (Ahmad et al. 2016). Superoxide dismutase improves the disproportionation of O2ˉ to H2O2 and O2 and hence decreases the oxidative stress. It helps in elimination of O2ˉ and reduces the menace of OH formation under heavy metal stress (Gopavajhula et al. 2013). Ascorbate peroxidase is involved in degradation of H2O2 and reduces oxidative stress in plants (Kangasjärvi et al. 2008). Current study showed increased accumulation of SOD and APX in K supplemented plants (Figure 2). Our results are in agreement with Szczerba et al. (2009) who reported that K helps in detoxification of H2O2 by improving activity of SOD and APX in supplemented plants. Peroxidase is also an important enzyme involved in mechanism of stress reduction in plants (Emamverdian et al. 2015).
Phyto-remedial detoxification of arsenic by Pistia stratiotes and assessment of its anti-oxidative enzymatic changes
Published in Bioremediation Journal, 2019
Mahasweta Paul, Chandrima Goswami, Meenakshi Mukherjee, Tarit Roychowdhury
Ascorbate peroxidase eliminates the potentially harmful H2O2 (Srivastava et al. 2005; Sandalio et al. 2001). In the present study, the ascorbate peroxidase activity (APX) in Pistia stratiotes was measured at an interval of 7 days upto a period of 28 days with exposure to different initial arsenic concentrations (10, 50, 100, and 200 ppb). The activity of the enzyme has been expressed as units of enzyme/gram of plant tissue and the measurements of the activity are given in Figure 4. Ascorbate peroxidase activity varied across the 28-day period, with the activity first indicating an increased presence on 7th day of measurement. For 10 and 50 ppb As, exposure after 14th day of treatment, APX activity dramatically decreased, might be due to insufficiency of ascorbate as APX is labile when ascorbate is low and becomes more prone to inactivation by protein inhibitors (Khan et al. 2009). This followed by a slight increase in enzyme activity on day 21 as well as on day 28 as the plants continued to be exposed to arsenic at concentrations of 10 and 50 ppb. With 100 and 200 ppb As exposure, APX activity initially increased but decreased on 28th day and 21st day of measurement, respectively, may be due to similar reasons. Despite the absence of significant elevated levels of APX activity, the amount of enzyme activity remained at a higher end in the plants exposed to the arsenic contaminated water than in the control plants because of induced stress response. This indicates that presence of arsenic contamination in water induced oxidative stress in plants (Leao et al. 2014). The reactive oxygen species produced with arsenic exposure in plants is typically known to induce an increase in ascorbate (Finnegan and Chen 2012). This stimulation in activity of peroxidase (Ganesh et al. 2008) is an indication of a stress situation in plants. Peroxides that use ascorbate as the hydrogen donor, have an important function of detoxifying H2O2 (Sinha, Saxena, and Singh 2005). Similar results of increase in activity of APX in root tissues of fern species Pteris vittata, P. ensiformis, and N. exaltata on exposure to 300 µM of arsenate has been reported by Srivastava et al. (2005).
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].