Mentha pulegium L. is a medicinal and aromatic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pronounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K⁺ uptake, as well as an increase in Na⁺ levels in all organs. Considering the response of antioxidant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equivalent g⁻¹ dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH scavenging ability with the lowest IC₅₀ value (0.27 µg ml⁻¹) in comparison with control which exhibited IC₅₀ equal to 0.79 µg ml⁻¹ .
Seedlings of sorghum varieties (M35-1, a drought tolerant species; SPV-839, a drought sensitive one) differing in their drought tolerance were subjected to 150 mM NaCl stress for a short duration of time (up to 72 h). Both the varieties failed to exhibit efficient ion exclusion mechanism like that of salt tolerant species, but in turn resulted in higher accumuiation of Na+ and Cl- ions over a period of 72 h salt stress. In addition, accumulation of calcium, potassium and proline in seedlings of sorghum varieties was moderate to short-term NaCl stress. The modulation of antioxidant components significantly diverged between the two varieties during seed germination, further the efficiency of antioxidant scavenging system is maintained during short-term NaCl treatments. In compari son to tolerant variety, the sensitive variety depicted higher SOD activity under control and salinity treatments but specific activity of catalase was significantly reduced. In contrast, drought tolerant variety exhibited efficient hydrogen peroxide scavenging mechanisms with higher catalase and GST activities under control and salt stress conditions, but not in the sensitive one. In conclusion, our comparative studies indicate that drought tolerant and susceptible varieties of sorghum induce efficient differential oxidative components of enzymatic machinery for scavenging ROS thereby alleviating the oxidative stress generated by salt stress during seedling growth.
Relatively little is known about the direct influence of acid rain (AR) on pro-and antioxidative changes in plant cells. Intercompartmental differences between cytosol and mitochondria were not studied before. Aboveground parts of plants treated with different pH variants of AR and prooxidative changes (lipid peroxidation) as well as antioxidative enzyme activities (ascorbate peroxidase, APx; glutathione peroxidase, GSH-Px) in the cytosolic and mitochondrial fractions were examined. The character of changes in antioxidative enzyme activities and of prooxidative alterations was closely connected with the cell com partment as well as with pH and time after treatment. The activity of both APx and GSH-Px increased more intensively in cytosol. Contrastingly, strong induction of lipid peroxides formation was observed in the mitochondrial fraction. The results suggest that cucumber mitochondria are more susceptible to oxidative damage caused by AR than cytosol. Antioxidative defense of cytosol appeared to provide sufficient protection against the oxidative stress imposed by AR.
The effects of hypoxia caused by complete submerging of Mnium undulatum gametophores in water, on their photosynthetic activity and the activity of two antioxidative en zymes: superoxide dismutase (SOD) and catalase (CAT) were investigated. The net photosynthesis was strongly inhibited throughout the experiment, and the strong drop in the maximum quantum yield of the PSII (Fv / Fm) was also observed. Three classes of SOD: MnSOD, FeSOD, Cu/ZnSOD and three isoforms of Cu/ZnSOD were identified. A significant decrease in activity of MnSOD, FeSOD and one Cu/ZnSOD isoform was observed after 24 and 48 h of hypoxia. FeSOD activity decreased already after 1 h of submerging in water and its activity remained at the low level during whole period of the experiment. CAT activity was also strongly inhibited in response to hypoxia stress. The obtained results suggest relationships between photosynthetic activity and antioxidative system in M. undulatum gametophores under oxygen deficiency stress.
The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione S-transferase (GST) as well as proline content were studi ed in leaves and roots of14 day-old pea plants treated with NiSO4 (10, 100, 200 pM) for 1,3, 6 and 9 day s. Exposure of pea plants to nickel (Ni) resulted in the decrease in CuZnSOD as well as total SOD activities in both leaves and roots. The activity of APX in leaves of plants treated with 100 and 200 pM Ni increased following the 3rd day after metal application, while in roots at the end of the experiment the activity of this enzyme was significantly reduced. In both organs CAT activity generally did not change in response to Ni treatment. The activity of GST in plants exposed to high concentrations of Ni increased, more markedly in roots. In both leaves and roots after Ni application accumulation of free proline was observed, but in the case of leaves conceniraiion of this amino acid increased eariier and to a greater extent than in roots. The results indicate that stimulation of GST activity and accumulation of proline in the tissues rather than antioxidative enzymes are involved in response of pea plants to Ni stress.
Radish (Raphanus sativus L.) is commonly grown in urban and suburban areas where the soil may be polluted with heavy metals such as Cu or Pb. In this study, short exposure of radish plantlets to 0.5 mM Cu or Pb in nutrient solution (two days) in growth chamber conditions elicited an antioxidative response, measured in terms of lipid peroxidation, protein and proline accumulation, and peroxidase and catalase activity. Longer exposure to Cu or Pb when radish was grown outdoors for 50 days in pots filled with field soil with different Cu and Pb content also resulted in higher lipid peroxidation and proline accumulation, and altered protein content and enzyme activity. The tested parameters of radish antioxidative responses to heavy metal stress differed depending on plant part (leaf or hypocotyl) and stress intensity (heavy metal content in growth medium, exposure duration). The reported data show that plants grown in soil from sites where this crop could be cultivated do show an oxidative stress response similar but not identical to that seen under laboratory treatment with heavy metals.
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