Wahbi Djebali

Effects of exogenous salicylic acid pre-treatment on cadmium toxicity and leaf lipid content in Linum usitatissimum L.

The effects of salicylic acid (SA) on cadmium (Cd) toxicity in flax plants were studied by investigating plant growth, lipid peroxidation and fatty acid composition. Cadmium inhibited biomass production as well as the absorption of K, Ca, Mg and Fe. Furthermore, it dramatically increased Cd accumulation in both roots and shoots. The pre-soaking of dry flax grains in SA-containing solutions partially protected seedlings from Cd toxicity during the following growth period. SA treatment decreased the uptake and the transport of Cd, alleviated the Cd-induced inhibition of Ca, Mg and Fe absorption and promoted plant growth. At leaf level, Cd significantly decreased both total lipid (TL) and chlorophyll (Chl) content and enhanced electrolyte leakage and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. Concomitantly, Cd caused a shift in fatty acid composition, resulting in a lower degree of their unsaturation. SA pre-soaking ameliorated the increased electrolyte leakage as well as Chl, MDA and TL content. SA particularly increased the percentage of linolenic acid and lowered that of palmitic acid by the same proportion. These results suggest that SA could be used as a potential growth regulator and a stabilizer of membrane integrity to improve plant resistance to Cd stress.

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings.

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.

Effects of long-term cadmium exposure on growth and metabolomic profile of tomato plants

The response of tomato plants to long-term cadmium exposure was evaluated after a 90-days long culture in hydroponic conditions (0, 20, and 100 μM CdCl(2)). Cadmium preferentially accumulated in roots, and to a lower extent in upper parts of plants. Absolute quantification of 28 metabolites was obtained through (1)H NMR, HPLC-PDA, and colorimetric methods. The principal component analysis showed a clear separation between control and Cd treated samples. Proline and total ascorbate amounts were reduced in Cd-treated leaves, whereas α-tocopherol, asparagine, and tyrosine accumulation increased, principally in 100 μM Cd treated leaves. Carotenoid and chlorophyll contents decreased only in 100 μM Cd-mature-leaves, which correlate with a reduced expression of genes essential for isoprenoid and carotenoid accumulations. Our results show that tomato plants acclimatize during long-term exposure to 20 μM Cd. On the contrary, 100μM Cd treatment results in drastic physiological and metabolic perturbations leading to plant growth limitation and fruit set abortion.

Salicylic acid increases tolerance to oxidative stress induced by hydrogen peroxide accumulation in leaves of cadmium-exposed flax (Linum usitatissimum L.)

The aim of this study is to investigate the impacts of exogenous salicylic acid (SA) pretreatments on hydrogen peroxide (H2O2) accumulation, protein oxidation, and H2O2-scavenging enzymes in leaves of Cd-treated flax seedlings. Cd-enhanced H2O2 levels were related to increased activities of guaiacol peroxidase (POX, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11), and were independent of changes in catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) activities. In control flax seedlings, exogenous SA pretreatments inhibited the activity of CAT, resulted in an enhanced production of H2O2 suggesting that SA requires H2O2 to initiate an oxidative stress. However, although leaves of Cd-free flax seedlings pretreated with SA accumulated in vivo H2O2 by 1.2-fold compared with leaves of Cd-only exposed ones; the damage to growth and proteins after the exposure to Cd was significantly less, indicating that SA can regulate the Cd-induced oxidative stress. Moreover, the Cd-treated seedlings primed with SA exhibited a higher level of total antioxidant capacities and increased activities of H2O2-detoxifying enzymes.

Influence of salicylic acid pre-treatment on cadmium tolerance and its relationship with non-protein thiol production in flax root

Dose-dependent changes in cadmium (Cd) tolerance, non-protein thiol (NP-SH) production and their relationship were investigated in sixteen-day-old flax ( Linum usitatissimum L.) seedlings derived from seeds pre-soaked with various salicylic acid (SA) doses and grown hydroponically under increased Cd concentrations (0, 50 and 100 μM CdCl 2 ). The results show that single Cd subjection decreased root elongation as expressed by tolerance index (TI). Moreover, an overproduction of NP-SH was detected in both roots and shoots. These Cd toxicity effects were directly related to the high levels of Cd amounts in flax tissues as expressed by root and shoot Cd bioaccumulation factors (BAF). In addition, Cd-tolerance of roots TI was negatively correlated with changes in root BAF but positively correlated with shoot BAF. However, positive correlation was illustrated between root TI and NP-SH contents. SA considerably reversed the Cd-induced decrease in root growth parameters and TI. Moreover, in Cd-treated plants, SA pre-soaking prevented Cd accumulation in the shoot as consequence of significant decreases in BAF of roots, Cd transport estimated by the translocation factor (TF) and shoot BAF, respectively. Interestingly, SA pre-treatment reduced BAF of roots and shoots, enhanced NP-SH production in roots and decreased it in leaves. These results suggest that SA might play a preventive role in Cd uptake, sequestration and translocation processes based primarily in roots where SA-enhanced NP-SH contribute to the improvement of flax tolerance to Cd stress. Key words: Cadmium, salicylic acid, bioaccumulation, growth, non-protein thiols, Linum usitatissimum .

Salicylic acid increases tolerance to oxidative stress induced by hydrogen peroxide accumulation in leaves of cadmium-exposed flax

The aim of this study is to investigate the impacts of exogenous salicylic acid (SA) pretreatments on hydrogen peroxide (H2O2) accumulation, protein oxidation, and H2O2-scavenging enzymes in leaves of Cd-treated flax seedlings. Cd-enhanced H2O2 levels were related to increased activities of guaiacol peroxidase (POX, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11), and were independent of changes in catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) activities. In control flax seedlings, exogenous SA pretreatments inhibited the activity of CAT, resulted in an enhanced production of H2O2 suggesting that SA requires H2O2 to initiate an oxidative stress. However, although leaves of Cd-free flax seedlings pretreated with SA accumulated in vivo H2O2 by 1.2-fold compared with leaves of Cd-only exposed ones; the damage to growth and proteins after the exposure to Cd was significantly less, indicating that SA can regulate the Cd-induced oxidative stress. Moreover, the Cd-treated seedlings primed with SA exhibited a higher level of total antioxidant capacities and increased activities of H2O2-detoxifying enzymes.

Exogenous salicylic acid protects phospholipids against cadmium stress in flax (Linum usitatissimum L.)

Salicylic acid (SA) promotes plant defense responses against toxic metal stresses. The present study addressed the hypothesis that 8-h SA pretreatment, would alter membrane lipids in a way that would protect against Cd toxicity. Flax seeds were pre-soaked for 8h in SA (0, 250 and 1000µM) and then subjected, at seedling stage, to cadmium (Cd) stress. At 100µM CdCl2, significant decreases in the percentages of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (MGDG) and changes in their relative fatty acid composition were observed in Cd-treated roots in comparison with controls. However, in roots of 8-h SA pretreated plantlets, results showed that the amounts of PC and PE were significantly higher as compared to non-pretreated plantlets. Additionally, in both lipid classes, the proportion of linolenic acid (18:3) increased upon the pretreatment with SA. This resulted in a significant increase in the fatty acid unsaturation ratio of the root PC and PE classes. As the exogenous application of SA was found to be protective of flax lipid metabolism, the possible mechanisms of protection against Cd stress in flax roots were discussed.

Effects of Exogenous Salicylic Acid on the Antioxidative System in Bean Seedling Treated with Manganese.

In the present study we investigated the role of salicylic acid (SA) in regulating Mn-induced oxidative stress in bean (Phaseolus vulgaris) leaves. Exposure of plants to 100 μM Mn inhibited biomass production and intensively increased Mn accumulation in leaves. Concomitantly, Mn significantly enhanced protein carbonyl, H2O2 content and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. SA (10, 50 and 100 μM) pretreatment alleviated the negative effect of Mn on plan growth and led to decrease in oxidative stress induced by Mn stress. Furthermore, SA enhanced the activities of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), but lowered that of superoxide dismutase (SOD, EC 1.15.1.1) and guaiacol peroxidase (POD, EC Original Research Article Saidi et al.; BBJ, 6(3): 93-100, 2015; Article no.BBJ.2015.031 94 1.11.1.7). The data suggest that the beneficial effect of SA could be related to avoidance of oxidative damage upon exposure to Mn thus reducing the negative consequences of oxidative stress caused by Mn toxicity.