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Ascorbic Acid
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
The ascorbate content of chloroplasts is generally between 10 and 50 mM, but values as high as 75 mΜ have been reported.4,5,22 The chloroplasts contain only 20 to 40% of the ascorbate present in the mesophyll cells22,30,34,35 and 10 to 50% of the leaf glutathione.34,36 These results demonstrate that a high proportion of the leaf ascorbate and glutathione exists in the extra-chloroplast compartment of the leaf cell. Ascorbate is found both in the cytosol and vacuole; indeed, ascorbate may be synthesized outside of the chloroplast. However, this ascorbate is accessible to the chloroplast because the chloroplast envelope membrane contains a specific ascorbate translocator.37,38 The ascorbate-glutathione cycle can operate efficiently in both the chloroplast and cytosol compartments with the transport of ascorbate and reducing equivalents (via the phosphate translocator) forming a redox link between the two compartments (Figure 3). While the ascorbate-glutathione cycle has been most extensively studied in chloroplasts, there is good evidence that all of the necessary enzymes of the cycle are also located in the cytosol of both green and nongreen tissues.34,39,40 It is clear that there are both cytosolic and chloroplastic isoforms of ascorbate peroxidase.41 The pea leaf cytosolic isoenzyme has been purified to homogeneity and characterized.42 Anderson et al.37 found only 30% of the total leaf dehydroascorbate reductase in spinach leaf chloroplasts, while Gillham and Dodge34 found 65% of the total enzyme activity in pea chloroplasts. Both authors found 70% of the total glutathione reductase (EC 1.6.4.2) activity in the chloroplasts, as did Edwards et al.43 These authors43 found that 3% of the pea leaf extrachloroplastic glutathione reductase was localized in the mitochondria and 27% in the cytosol.
Heavy Metal Pollution and Medicinal Plants
Published in Azamal Husen, Environmental Pollution and Medicinal Plants, 2022
Allah Ditta, Naseer Ullah, Xiaomin Li, Ghulam Sarwar Soomro, Muhammad Imtiaz, Sajid Mehmood, Amin Ullah Jan, Muhammad Shahid Rizwan, Muhammad Rizwan, Iftikhar Ahmad
HM stress induces depletion of molecular oxygen to create intermediates like hydrogen peroxide (H2O2), hydroxyl radicals (OH), and superoxide radicals (O2) that are significantly hazardous or toxic for the plants’ metabolic activities. Radicals of superoxide could suppress metallic ions (Mn+) in organelles like Fe3+ and Cu2+. The synthesis of superoxide radicals through H2O2 and O2 could be catalysed by superoxide dismutase (Heldt, 2005). Hydroxyl radicals are created via the interaction of H2O2 with metal ions by a reduction reaction (Heldt, 2005). Hydroxyl radicals are quite dangerous and can degrade proteins or lipoproteins. No defence antibodies against OH radicals is found in the plant cell. Consequently, the avoidance of the reduction process by removing superoxide radicals utilizing SOD is important for cells. Hydrogen peroxide negatively affects multiple metabolites and its deleterious effects can be controlled by APX and CAT (Heldt, 2005). Catalase is a crucial enzyme, which catalyses oxygen and water to break down hydrogen peroxide and defends plants against ROS (Chelikani et al., 2004). Ascorbate peroxidase (APX) is an additional significant enzyme for the reduction of H2O2. Ascorbate, an essential plant antioxidant, is oxidized and transformed into a monodehydroascorbate radical that is instinctively converted to ascorbate via ferredoxin reduction. In a selective manner, dehydroascorbate and ascorbate could be integrated into two molecules of monodehydroascorbate. Through the redox process catalysed via dehydroascorbate reductase, dehydroascorbate may also have been transformed into ascorbate via glutathione (GSH). Glutathione, consisting of three amino acids, i.e. glycine, glutamate, and cysteine, is indeed an essential antioxidant within plant tissues. The oxidation of GSH contributes to the production of a disulfide (GSSG) bond of two molecules of glutathione among the compounds of cysteine. GSSG reduction is catalysed by the glutathione reductase enzyme and regulated by NADPH as the reductant (Heldt, 2005).
Improvement of ionizing gamma irradiation tolerance of Chlorella vulgaris by pretreatment with polyethylene glycol
Published in International Journal of Radiation Biology, 2020
Seyed Ali Hosseini Tafreshi, Peyman Aghaie, Mohammad Amin Toghyani, Ahmad Ramazani-Moghaddam-Arani
The plant and algae employ both enzymatic and non-enzymatic defense mechanisms to ameliorate the negative effects of free radical molecules (i.e. ROS) on sub-cellular compartments under stress conditions. (Kusvuran et al. 2016; Alscher and Hess 2017; Anaraki et al. 2018). It was found that the correlated increased activity of catalase and ascorbate peroxidase results in the faster removal of hydrogen peroxide by the ascorbate glutathione cycle. This could more efficiently reduce the oxidative damage caused by free oxygen radicals that contributed to the DNA or the cell genome damage (Nimse and Pal 2015; Sofo et al. 2015; Maruta et al. 2016; Hamed, Selim et al. 2017; Ighodaro and Akinloye 2018). In a study on the effect of gamma irradiation on the antioxidant defense system of algae Zygnema sp., it was demonstrated that irradiations at intensity of up to 3 kGy had a significant effect on increasing the activity of antioxidant enzymes (Choi et al. 2015). In another study on two samples of green algae including C. vulgaris and Chlamydomonas rhinarditis, peroxidase activity at the concentration of 25% PEG has shown a significant increase compared to the control sample (Chan et al. 1981). It is suggested that PEG could act as an inducing agent of the enzymatic antioxidant system of C. vulgaris algae under gamma-free and gamma radiation conditions.
Heme metabolism as a therapeutic target against protozoan parasites
Published in Journal of Drug Targeting, 2019
Guilherme Curty Lechuga, Mirian C. S. Pereira, Saulo C. Bourguignon
T. cruzi also expresses a functional ascorbate peroxidase closely related to plants and L. major APx. Unlike Leishmania, T. cruzi ascorbate peroxidases (TcAPx) are located in the endoplasmic reticulum [174] and represent one of parasite’s defence line against oxidative stress. Despite increased sensitivity to hydrogen peroxide and reduced infectivity in vitro, TcAPx null mutants successfully establish a chronic infection in mice [175]. Furthermore, the role of TcAPx in benznidazole resistance is unclear. The expression of this enzyme in Bz resistant T. cruzi populations, in vivo selected and in vitro induced, were increased twofold and threefold, respectively [176]. But no difference in benznidazole susceptibility was found in TcAPx null mutants [175], although it was only tested in noninfective form and parasite’s genetic diversity were not considered.
Phytochemical, antioxidant, enzyme activity and antifungal properties of Satureja khuzistanica in vitro and in vivo explants stimulated by some chemical elicitors
Published in Pharmaceutical Biology, 2020
Farzaneh Fatemi, Mohammad Reza Abdollahi, Asghar Mirzaie-asl, Dara Dastan, Kalliope Papadopoulou
Nanoparticles could act as signal compounds inducing metabolic and physiological responses in Pelargonium zonale L. L’Hér. (Geraniaceae) (Hatami and Ghorbanpour 2014). Previous research reported that nanosilver particles could cause oxidative stress, raise lipid peroxidation, and catalase activity in Artemisia annua L. (Compositae) (Zhang et al. 2013). Also, some studies revealed that nanoparticles could activate plant antioxidant systems and increase activities of superoxide dismotase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) in spinach chloroplast (Lei et al. 2008). It was shown that MWCNTs had ability to enhance the growth of tobacco cells at different concentrations (Khodakovskaya et al. 2012). In this study, two separate experiments were performed. At the first experiment, different concentrations of MWCNTs and MeJA were applied on nodal segments cultures of S. khuzistanica grown in vitro. The second one was performed to investigate the potential effects of spraying 100 mg/L MWCNTs and 200 mg/L SA at different time points on in vivo plants. Phytochemical responses, including RA contents, enzyme activities; catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) were measured in both in vitro and in vivo treated plants. Antioxidant activities of the extracts (DPPH and β-carotene) were measured in in vivo plants exposed to MWCNTs and SA treatments at different times from initial treatments. Finally, the antifungal effects of in vivo and in vitro extracts and also inhibitory impacts of callus were evaluated.