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- Growth, chlorophyll fluorescence and mineral nutrition in the halophyte Tamarix gallica cultivated in combined stress conditions: Arsenic and NaClPublication . Sghaier, Dhouha Belhaj; Duarte, Bernardo; Bankaji, Insaf; Caçador, Isabel; Sleimi, NoomeneTrace metal elements can cause various environmental and health issues due to their accumulation and integration in the food chain. In the present study, we determined the major toxic effects of arsenic on physiological behaviour of plants. For this propose, several combinations of high salinity and arsenic (As) concentrations were applied to the halophytic shrub, Tamarix gallica, by growing for three months with an irrigation solution supplemented with different concentrations of As (0, 200, 500 and 800M) with and without 200mM NaCl. The effect of the combined stress conditions on growth, physiological patterns and biochemical parameters were also assessed. The results demonstrated that T. gallica is a tolerant plant regarding arsenic. The photosynthesis apparatus Fo, Fm and Fv fluorescence, as well as Fv/Fm were not affected by As nor by As combined with salt. Likewise, pigment and nutrient (K+, Ca2+ and Mg2+) contents were not affected either. However, the study results revealed that As adversely and significantly influenced the growth with increasing the concentration of As. Despite shoots growth reduction, the present research demonstrates that T. gallica is able to cope with high external concentrations of As (under 500μM) alone or in combination with NaCl.
- Leaf fatty acid remodeling in the salt-excreting halophytic grass Spartina patens along a salinity gradientPublication . Duarte, Bernardo; Matos, Ana Rita; Marques, João Carlos; Caçador, IsabelSpartina patens is a highly dispersed halophytic grass invader in Mediterranean marshes. It is also characterized by having a high degree of resistance to salinity, one of the main drivers of plant zonation in salt marshes. Nevertheless, the physiological basis behind the extreme resistance of S. patens requires more detailed studies. In the present work, we aimed to study how membrane fatty acid remodeling could contribute to the resistance of this plant to salt. Spartina patens individuals exposed to increasing levels of salinity and its leaf fatty acid profile under lipid peroxidation products evaluated under all tested concentrations. A significant increase in the relative amounts of the saturated fatty acids (SFA) was observed, namely palmitic acid (C16:0), essential for PS II functioning, and stearic (C18:0) acid. The chloroplastidial trans-hexadecenoic acid (C16:1t) as well as the polyunsaturated linoleic (C18:2) and linolenic (C18:3) acids showed significant decreases in all the salt treatments. These changes led to a reduction in the double bond index in salt-treated plants which reflects reduction of the fluidity of the chloroplast membranes, which could contribute to maintain the membrane impermeable to the toxic exogenous Na. Despite the decrease observed in the total fatty acid contents in plants exposed to high salt concentrations the amounts of lipid peroxidation products decreased highlighting the resistance of this species towards toxic exogenous salt concentrations. Membrane fatty acid remodeling could represent an efficient mechanism to maintain the photosynthetic machinery of S. patens highly efficient under salt stress.
- Biochemical and photochemical feedbacks of acute Cd toxicity in Juncus acutus seedlings: The role of non-functional Cd-chlorophyllsPublication . Santos, D.; Duarte, Bernardo; Caçador, IsabelThe increasing metal pollution in salt marshes and its influence on the plants that inhabit these ecosystems, has become a major concern with serious implications on the species establishment. Juncus acutus is a highly common halophyte specie in Portuguese marshes. Seeds from his specie were exposed to a range of different Cd concentrations (0.05, 0.1, 0.5 and 1 μM) in order to evaluate the effects of acute Cd stress on seed germination and growth as well as on seedling pigment composition, photosynthetic apparatus and oxidative stress biomarkers. Seedling length was higher than in control in every Cd treatment, however biomass showed a decrease. It was also observed that increasing Cd treatments, lead to a proportional increase in the Cd tissue concentration. Also the Cd-substituted chlorophylls showed an increase with increasing Cd doses that were applied. This substitution results in a non-functional chlorophyll molecule, highly unstable under moderate light intensities which inevitably reduces the efficiency of the LHC II. As consequence, there was a decrease in the use-efficiency of the harvested energy, leading to a decay in the photosynthetic capacity and energy accumulation, which was dissipated as heat. As for the antioxidant enzymes, SOD and APX presented higher activity, responding to increasing cadmium concentrations. Thus, becomes evident that Cd affects negatively, both biochemically and photochemically, the establishment by seed process of J. acutus highlighting the potential of the use of this specie seed as potential sentinel and ecotoxicity test in extreme conditions.
- Investigating the physiological mechanisms underlying Salicornia ramosissima response to atmospheric CO2 enrichment under coexistence of prolonged soil flooding and saline excessPublication . Pérez-Romero, Jesús Alberto; Duarte, Bernardo; Barcia-Piedras, Jose-Maria; Matos, Ana Rita; Redondo-Gómez, Susana; Caçador, Isabel; Mateos-Naranjo, EnriqueA 45-days long climatic chamber experiment was design to evaluate the effect of 400 and 700 ppm atmospheric CO2 treatments with and without soil water logging in combination with 171 and 510 mM NaCl in the halophyte Salicornia ramosissima. In order to ascertain the possible synergetic impact of these factors associate to climatic change in this plant species physiological and growth responses. Our results indicated that elevated atmospheric CO2 concentration improved plant physiological performance under suboptimal root-flooding and saline conditions plants. Thus, this positive impact was mainly ascribed to an enhancement of energy transport efficiency, as indicated the greater PG, N and Sm values, and the maintaining of carbon assimilation capacity due to the higher net photosynthetic rate (AN) and water use efficiency (iWUE). This could contribute to reduce the risk of oxidative stress owing to the accumulation of reactive oxygen species (ROS). Moreover, plants grown at 700 ppm had a greater capacity to cope with flooding and salinity synergistic impact by a greater efficiency in the modulation in enzyme antioxidant machinery and by the accumulation of osmoprotective compounds and saturated fatty acids in its tissues. These responses indicate that atmospheric CO2 enrichment would contribute to preserve the development of Salicornia ramosissima against the ongoing process of increment of soil stressful conditions linked with climatic change.
- Assessing of tolerance to metallic and saline stresses in the halophyte Suaeda fruticosa: The indicator role of antioxidative enzymesPublication . Bankaji, Insaf; Caçador, Isabel; Sleimi, NoomeneMany areas are simultaneously affected by high concentrations of salts and trace metal elements (TME), the latter constituting a serious threat to human health. In the present study, we determined the combined effect of high salinity and toxic levels of trace elements on physiological behavior of the halophytic species Suaeda fruticosa. Plants were cultivated for three months with an irrigation solution supplemented separately with different concentrations of Pb2+ and Zn2+ (0, 200, 400 and 600 microM) with and without 200 mM NaCl. Growth, total chlorophyll, water status and ion nutrition were quantified and antioxidant enzyme activities [ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and catalase (CAT)] were studied. Our results revealed that S. fruticosa has a strong ability to tolerate lead and zinc. This halophyte accumulated higher concentrations of TME in their roots. Growth parameters of S. fruticosa were not significantly affected by TME. An enhancement of Ca2+ concentration accompanied by a decrease of Mg2+ content was observed under Pb2+ or Zn2+ treatments whereas K+ content was not affected by TME. Of the antioxidant enzymes, the activity of CAT and APX was increased by metal stress. However, the activity of GPX was diminished by increasing TME concentrations. It was concluded that NaCl 200 mM had a positive impact on the response of S. fruticosa to Zn2+ toxicity, acting through a decrease in Zn absorption.
- Disentangling the effect of atmospheric CO2 enrichment on the halophyte Salicornia ramosissima J. Woods physiological performance under optimal and suboptimal saline conditionsPublication . Pérez-Romero, Jesús Alberto; Idaszkin, Yanina Lorena; Barcia-Piedras, Jose-Maria; Duarte, Bernardo; Redondo-Gómez, Susana; Caçador, Isabel; Mateos-Naranjo, EnriqueA mesocosm experiment was designed to assess the effect of atmospheric CO2 increment on the salinity tolerance of the C3 halophyte Salicornia ramosissima. Thus, the combined effect of 400 ppm and 700 ppm CO2 at 0, 171 and 510 mM NaCl on plants growth, gas exchange, chlorophyll fluorescence parameters, pigments profiles, antioxidative enzyme activities and water relations was studied. Our results highlighted a positive effect of atmospheric CO2 increment on plant physiological performance under suboptimal salinity concentration (510 mM NaCl). Thus, we recorded higher net photosynthetic rate (AN) values under saline conditions and 700 ppm CO2, being this effect mainly mediated by a reduction of mesophyll (gm) and biochemical limitation imposed to salt excess. In addition, rising atmospheric CO2 led to a better plant water balance, linked with a reduction of stomatal conductante (gs) and an overall increment of osmotic potential (Ѱo) with NaCl concentration increment. In spite of these positive effects, there were no significant biomass variations between any treatments. Being this fact ascribed by the investment of the higher energy fixed for salinity stress defence mechanisms, which allowed plants to maintain more active the photochemical machinery even at high salinities, reducing the risk of ROS production, as indicated an improvement of the electron flux and a rise of the energy dissipation. Finally, the positive effect of the CO2 was also supported by the modulation of pigments profiles (mainly zeaxhantin and violaxhantin) concentrations and anti-oxidative stress enzymes, such as superoxide dismutase (SOD) and ascorbate peroxidase (APx).
- Accumulation potential of Atriplex halimus to zinc and lead combined with NaCl: Effects on physiological parameters and antioxidant enzymes activitiesPublication . Bankaji, I.; Pérez-Clemente, R.M.; Caçador, Isabel; Sleimi, N.An experiment in this study was designed to investigate the effect of different concentrations of Zn2+ or Pb2+ (0, 200, 400 and 600 μM) with NaCl (0, 200 mM), on the morphological and physiological parameters as well as the antioxidative response of the halophytic species Atriplex halimus. Results showed that Pb2+ had no significant impact on biomass production while Zn2+ significantly affected plant development mainly at high concentration, 600 μM. Total chlorophyll content did not change significantly under elevation concentrations of Zn2+ when compared to control. However, there was a modest decrease in total chlorophyll concentration in the leaves of A. halimus grown in a medium supplemented with 600 μMPb2+ and with combined stress Pb2+/NaCl. Zn2+ and Pb2+ contents in tissues were higher in the belowground organs of this halophyte. Overall results pointed out that application of different concentrations of Zn2+ or Pb2+ disturbed status of nutrients in A. halimus. Analysis of antioxidant enzymes [ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and catalase (CAT)] showed that the activity was diminished by increasing Zn2+ concentrations in the medium. Whereas, the addition of Pb2+ in the medium increased CAT activity and decreased APX activity.