Functional indicators of response mechanisms to nitrogen deposition, ozone, and their interaction in two Mediterranean tree species

The effects of nitrogen (N) deposition, tropospheric ozone (O3) and their interaction were investigated in two Mediterranean tree species, Fraxinus ornus L. (deciduous) and Quercus ilex L. (evergreen), having different leaf habits and resource use strategies. An experiment was conducted under controlled condition to analyse how nitrogen deposition affects the ecophysiological and biochemical traits, and to explore how the nitrogen-induced changes influence the response to O3. For both factors we selected realistic exposures (20 kg N ha-1 yr-1 and 80 ppb h for nitrogen and O3, respectively), in order to elucidate the mechanisms implemented by the plants. Nitrogen addition resulted in higher nitrogen concentration at the leaf level in F. ornus, whereas a slight increase was detected in Q. ilex. Nitrogen enhanced the maximum rate of assimilation and ribulose 1,5-bisphosphate regeneration in both species, whereas it influenced the light harvesting complex only in the deciduous F. ornus that was also affected by O3 (reduced assimilation rate and accelerated senescence-related processes). Conversely, Q. ilex developed an avoidance mechanism to cope with O3, confirming a substantial O3 tolerance of this species. Nitrogen seemed to ameliorate the harmful effects of O3 in F. ornus: the hypothesized mechanism of action involved the production of nitrogen oxide as the first antioxidant barrier, followed by enzymatic antioxidant response. In Q. ilex, the interaction was not detected on gas exchange and photosystem functionality; however, in this species, nitrogen might stimulate an alternative antioxidant response such as the emission of volatile organic compounds. Antioxidant enzyme activity was lower in plants treated with both O3 and nitrogen even though reactive oxygen species production did not differ between the treatments

Effects of triacontanol on ascorbate-glutathione cycle in Brassica napus L. exposed to cadmium-induced oxidative stress.

The ability of exogenous triacontanol (TRIA), a plant growth regulator, to reduce Cd toxicity was studied in canola (Brassica napus L.) plants. The following biological parameters were examined in canola seedlings to investigate TRIA-induced tolerance to Cd toxicity: seedling growth, chlorophyll damage and antioxidant response. In particular, TRIA application reduced Cd-induced oxidative damage, as shown by reduction of ROS content, lipoxygenase (LOX) activity and lipid peroxidation level. TRIA pretreatment increased non-enzymatic antioxidant contents (ascorbate, AsA, glutathione and GSH), phytochelatin content (PCs) and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), monodehydroascorbate reductase (MDHAR), dehydro ascorbate reductase (DHAR), and glutathione reductase (GR), so reducing the oxidative stress. These results clearly indicate the protective ability of TRIA to modulate the redox status through the antioxidant pathway AGC and GSH, so reducing Cd-induced oxidative stress

Interaction of triacontanol and arsenic on the ascorbate-glutathione cycle and their effects on the ultrastructure in Coriandrum sativum L.

Exogenous application of triacontanol (TRIA) has the ability to mitigate the adverse effects of abiotic stresses by modulating a number of physio-biochemical processes in different plants. However, information about how its effects may be mediated under heavy metal stress is scanty. In this study, we evaluated how TRIA exerted its role against the toxicity of sodium arsenate in coriander (Coriandrum sativum L.). The activities of enzymes, including ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione-S-transferase (GST), were measured. In addition, the contents of ascorbate (ASC), dehydroascorbate (DHA), reduced glutathione (GSH) and some elements including both As and the nutrients Ca, Mg, Zn, K, P were determined. Results suggested that As decreased GSH, ASA and DHA contents, a clear indication of oxidative stress, but their amounts were raised by TRIA treatment. Also, As stress decreased plant Ca, Zn, K, Mg and P contents, while TRIA improved their uptake and inhibited As accumulation. As 200 μM treatment inhibited the activities of APX, MDHAR, DHAR, and GR, enzymes of the ascorbate-glutathione cycle (AGC). TRIA supplementation restored and even enhanced the activity of all the AGC enzymes. 10 μM TRIA treatment increased GST gene expression and activity to a greater extent than under only As treatment. TRIA-alone treatments did not change the mentioned parameters. Transmission electron microscopy (TEM) observations showed that TRIA was able to protect cells, and most of all chloroplasts, from As-induced damage. These results clearly indicate the protective role of TRIA in modulating the redox status of the plant system through the antioxidant AGC and GSH enzymes, which could counteract arsenic-induced oxidative stress

Reducing Arsenic Toxicity Stress in Soybean (Glycine max L.) by Using of Sodium Nitroprusside

Arsenic contamination is one of the most important compounds all over the world. Arsenic in different ways, including the formation of reactive oxygen species and membrane lipid peroxidation impairs growth of plants. In this study, the effect of arsenic and sodium nitroprusside (SNP) were evaluated on soybean. Soybean at four leaf stage was treated with different concentrations of arsenic (0, 150 and 300 mM) and SNP (0 and 100 mM), and then concentrations of hydrogen peroxide, proline, malondialdehyde and activity of antioxidant enzymes in its shoot were measured. The results showed that increasing concentration of arsenic in Hoagland solution reduced total chlorophyll content in the shoot and increased the activity of catalase and peroxidase significantly. It was also observed that treating plants with arsenic increased hydrogen peroxid accumulation which resulted in peroxidation of membrane lipids. Higher malondialdehyde content confirmed this result. Using SNP in the medium containing arsenic increased total chlorophyll content, activities of guaiacol peroxidase enzyme and ascorbate peroxidase, significantly. However, the catalase activity in this case decreased. Thus it can be concluded that using SNP, would reduce effectively the damage of oxidation

Study of interaction effect between triacontanol and nitric oxide on alleviating of oxidative stress arsenic toxicity in coriander seedlings

In this study, triacontanol (TRIA) and nitric oxide (NO) interaction on arsenic (As)-induced oxidative stress tolerance in coriander (Coriandrum sativum L.) plants was investigated. The results showed that As had a significant adverse effect on the plant’s biomass. The seedlings pretreated with TRIA and NO significantly increased growth reduction induced by the metalloid. The obtained results indicated that the application of TRIA and sodium nitroprusside (SNP) generally reduced oxidative markers such as of electrolyte leakage percentage, malondialdehyde and H2O2 contents under As toxicity, while application of As treatment without TRIA + SNP increased these oxidative parameters compared to the control. The non-enzymatic antioxidant contents such as total phenol, anthocyanin, carotenoid, ascorbic acid and reduced glutathione (GSH) were extracted and assayed from both control and treated plants. It was found that TRIA + SNP treatments have a profound effect on the antioxidant metabolism and caused an enhancement in non-enzymatic antioxidant potentials under As toxicity in coriander. Moreover, the results revealed a mutually amplifying reaction between TRIA and NO in reducing As-induced damages

Trend of steady-state gas exchange parameters in <i>F</i>. <i>ornus</i>.

<p>The trend is shown as the mean and standard deviation (n = 5) for each treatment. Measurements were performed at the first, fourth, seventh, and tenth day of fumigation (DOF). Symbols over the bars indicate the significant factors (<i>p</i> < 0.05) affecting the gas exchange parameters: N, nitrogen effect; O₃, ozone effect; O₃ × N, interaction.</p

The outputs of biochemical analysis.

<p>They are shown for each treatment at the end of the experimental period for <i>F</i>. <i>ornus</i> (upper panel, from a to g) and <i>Q</i>. <i>ilex</i> (below panel, from h to p). Reactive oxygen species (ROS, %); superoxide dismutase, (SOD, inhibition rate %); catalase (CAT, U mg^-1 of protein); ascorbate peroxidase (APX, U mg^-1 of protein); total concentration of ascorbic acid (ASA, mg g^-1); oxidised ascorbic acid (DHA, mg g^-1); and glutathione (GSH, mg g^-1). Data are means ± standard deviation (n = 5), and bars not accompanied by the same letter are significantly different at <i>p</i> < 0.05, by using post hoc Student–Neuman–Keuls test.</p

Trend of steady-state gas exchange parameters in <i>F</i>. <i>ornus</i>.

<p>The trend is shown as the mean and standard deviation (n = 5) for each treatment. Measurements were performed at the first, fourth, seventh, and tenth day of fumigation (DOF). Symbols over the bars indicate the significant factors (<i>p</i> < 0.05) affecting the gas exchange parameters: N, nitrogen effect; O₃, ozone effect; O₃ × N, interaction.</p

Analysis of variance of JIP-test parameters for <i>F</i>. <i>ornus</i> and <i>Q</i>. <i>ilex</i>.

<p>Analysis of variance of JIP-test parameters for <i>F</i>. <i>ornus</i> and <i>Q</i>. <i>ilex</i>.</p