TY - JOUR
AU - Sebastiani, Luca
AB - Abstract Surfactants are widely used detergent ingredients and, thanks to their chemical properties, they are applied for remediation of sites polluted by heavy metals and organic contaminants, both in soil flushing and in phytoremediation. However, their direct effects on tree physiology especially in consociation with heavy metal pollution, as well as their possible absorption by plants, have not been appropriately investigated. In order to evaluate plant uptake/translocation of the surfactant sodium dodecyl sulfate (SDS) and the heavy metal zinc (Zn) in Populus alba L. Villafranca clone, SDS was applied alone (0.5 mM) or in combination with Zn (1 mM). Physiological effects on plant growth and photosynthetic performance were investigated. An increasing trend of Zn translocation towards basal leaves as a consequence of SDS co-treatment (1 mM Zn + 0.5 mM SDS; P = 0.03) was observed, proving the ability of SDS to improve heavy metals translocation. However, SDS exposure (both in 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS treated plants) resulted in the appearance of foliar necrosis that expanded with an acropetal trend and finally led to leaf abscission. This phenotype may be caused by the emergence of an additional stress during the experimental trial, which could be related to the dissociation of sodium (Na) ions from the dodecyl sulfate molecules in the hydroponic system. In fact, while liquid chromatography–tandem mass spectrometry measurements revealed that dodecyl sulfate is mainly retained at root levels, Na is translocated to the aerial parts of the plant. Introduction Surfactants are a class of compounds widely used throughout the world with numerous industrial applications, such as food, paints, plastics, pharmaceuticals, cosmetics, textiles, etc. (Cserháti et al. 2002). In particular, anionic surfactants are popular detergent ingredients, because of their straightforward synthesis and therefore low production costs. As a consequence of their widespread use and strong resistance to biodegradation, surfactants may persist in wastewater treatment systems at relatively high concentrations (Dirilgen and Ince 1995, Pettersson et al. 2000). Moreover, they are used for their ability to meliorate the solubility of petroleum hydrocarbons and heavy metals such as cadmium (Cd), zinc (Zn), copper (Cu) and lead in polluted soils, hence increasing their removal from the polluted site, both in soil flushing (Torres et al. 2007, Ramamurthy and Schalchian 2013) and in phytoremediation trials with herbaceous species (Liu et al. 2008, 2009, Almeida et al. 2009, Almansoory et al. 2015, Mao et al. 2015). Both these classes of contaminants (anionic surfactants and heavy metals) persist in water and soil but their effects on plants, and in particular the effects of their consociation, are very poorly studied. Surfactants are molecules with a high environmental impact (Cserháti et al. 2002, Kumar et al. 2014), and their ecotoxicity is a matter of increasing interest because of their continuous introduction into the aquatic environment via domestic and industrial wastewaters. Anionic surfactants such as sodium dodecyl sulfate (SDS) are amphipathic compounds, which interact readily with polar and apolar macromolecules, leading to membrane damage (Anderberg and Artursson 1993) and oxidative stress (Wang et al. 2016). The direct effect of SDS on plants in remediation trials has not been thoroughly investigated, because it can be degraded by some strains of Pseudomonas species that are able to use this molecule as carbon source (Chaturvedi and Kumar 2011, Paulo et al. 2013), as well as by photo electrochemical processes (Nguyen et al. 2016). SDS has been shown to have toxic effects on duckweed, where it affects chlorophylls, phenols content and the activity of stress enzymes (Dirilgen and Ince 1995, Forni et al. 2008, 2012). In Azolla pinnata R.Br. and Hydrilla verticillata (L.f.) Royle, chlorophyll content was found to decrease at all concentrations used (Pandey and Gopal 2010). An enhancement of reactive oxygen species production was found in mussels exposed to SDS (Messina et al. 2014). Zinc it is a heavy metal whose main source of input into soil and water are human activities such as mining operations, coal and waste combustion, smelting and steel processing, as well as sewage sludge application to land. Despite being a plant micronutrient, its effects on herbaceous and arboreal species when exposed to supraoptimal concentrations are well documented, for instance reduced yield, leaf chlorosis and necrosis, and imbalance of nutrients uptake (Chaney 1993, Subba et al. 2014, Benáková et al. 2017). Among tree species, the potential phytoremediation of heavy metals and organic pollutants (Sebastiani et al. 2004, Marmiroli et al. 2011, Pilipović et al. 2015, Pierattini et al. 2016a, 2016b) and in particular Zn (Di Baccio et al. 2003, Romeo et al. 2014) of poplar species has been widely explored. In poplar it has been demonstrated that high Zn concentrations determine an impairment of photosynthetic efficiency and alter leaf morphology and ultrastructure (Di Baccio et al. 2009, Todeschini et al. 2011). Recent literature demonstrate that Populus alba L. Villafranca clone showed the ability to take up Zn and organic pollutants like caffeine and erythromycin without exhibiting physiological disorders (Romeo et al. 2014, Pierattini et al. 2016a, 2016b), making it a great candidate for studying multiple factor stresses. The aim of this research was to explore the effects of surfactant–heavy metal combination in an hydroponic system. Two main aspects have been taken into account: (i) the SDS and Zn accumulation in poplar organs; and (ii) the photosynthetic and physiological responses of poplar under SDS and Zn treatments. Materials and methods Plant material and treatments Plantlets of P. alba L. Villafranca clone were transferred from Woody Plant Medium (WPM) half-strength solid medium in Magenta vessels (Lloyd and McCown 1980) to plastic pots filled with perlite (Laterlite, Milan, Italy; 43° 43′ 13.23″ N, 10° 24′ 10.34″ E) and closed in Plexiglas boxes able to maintain high humidity. These transplanted plantlets were acclimatized for 3 weeks in a growth chamber under controlled environmental conditions (21:18 °C day:night temperature, 50% humidity and a photoperiod of 16 h at maximum photon flux density of 400 μmol m−2 s−1 photosynthetically active radiation supplied by fluorescent lights). During the acclimation process the nutrient supply was gradually changed from liquid half-strength WPM to Hoagland’s solution (Arnon and Hoagland 1940), and the relative humidity was reduced from 100% to 65–70%. At the end of this acclimation period all the plants were able to grow at the humidity of the growth chamber (65–70%). After acclimation, plants of uniform size were transferred into singular plastic pots containing 4–8 Ø mm expanded Agrileca clay (Laterlite) in hydroponic conditions. Each plant was supplied with 1 l of a basic Hoagland’s solution renewed weekly continuously aerated by aquarium pumps (250 l h−1). Pots, substrate and hydroponic equipments were washed thoroughly with deionized water to avoid or limit detergents contamination. After 3 weeks acclimation to hydroponic conditions, five randomly selected plants were destructively sampled in order to determine the initial fresh (FW) and dry weight (DW) of roots, stem and leaves, stem length and leaves number. The remaining plants were randomly assigned to four treatments (n = 5): 1 mM Zn(NO3)2; 0.5 mM SDS; 1 mM Zn(NO3)2 + 0.5 mM SDS; or control. Control Hoagland nutritive solutions contained 1 μM Zn supplied as Zn(NO3)2, and 1 μM sodium (Na), supplied as Na2Mo4 2 H2O. The 1 mM Zn concentration was chosen as it is known to be sub-symptomatic for Villafranca clone, despite the high rate of metal accumulation of this clone (Romeo et al. 2014), while a concentration of 0.5 mM SDS can be found in studies concerning enhancement of phytoremediation in heavy metals-polluted soils (Liu et al. 2008). Each plant was supplied with 1 l of either control or treated Hoagland solution, which was renewed weekly. In order to avoid photodegradation of SDS, hydroponics pots were covered with black plastic tops. Moreover, the roots of the in vitro-derived plants were washed in NaOCl 7% solution before being put in hydroponics, to eliminate eventual microbial populations associated to roots. Growth parameters and photosynthetic pigments content After 21 days of treatments, five plants for each treatment were harvested, carefully rinsed with deionized water and separated into roots, stem and leaves for FW and DW determination (oven-dried at 70 °C until constant weight was achieved). Stem length and leaves number were also recorded. Leaf (LMR), shoot (SMR) and root (RMR) mass ratios were calculated as the ratio of the corresponding organ dry biomass to the total plant dry biomass. Relative growth rate was calculated for leaves (RGRl), stem (RGRs), roots (RGRr) and for the whole plant (RGRtot) according to the formula RGR = [ln (DWt) – ln (DWt0)]/t, where DWt is the dry weight at the sampling time, DWt0 is the dry weight at the start of the experiment and t is the time difference between the sampling time and the start of the experiment, expressed in days. Photosynthetic pigments contents were measured independently in apical, median and basal leaves in order to identify an eventual differential response based on leaf age and position. Using the leaf plastochron index (LPI; leaves can be progressively ranked from the first fully open but not yet completely expanded leaf LPI = 1; Dickmann 1971) leaves were separated into ‘apical’ (1 ≤ LPI ≤ 7), ‘median’ (7 < LPI ≤ 14) and ‘basal’ (LPI > 14). The apical portion of stem including developing leaves with LPI < 1 was included in the ‘apical’ pool. Briefly, extraction of photosynthetic pigments was performed overnight with HPLC-grade methanol (1:10, w/v) at 4 °C. HPLC separation of pigments was performed using a ZorbaxODS column (5 μm particle size, 250 × 4.6 mm Ø; Agilent Technologies, Milan, Italy). The gradient (flow rate 1 ml min−1) was set as follows: 15 min, 100% solvent A (acetonitrile/methanol, 75/25 v/v); 2.5 min linear gradient to 100% solvent B (methanol/ethyl acetate, 68/32 v/v), which continued isocratically for 10.5 min; 10 min column re-equilibration (100% solvent A). Detection wavelength, 445 nm. Standards of lutein, chlorophyll b, chlorophyll a and β-carotene (Sigma-Aldrich, Milan, Italy) were used to build calibration curves (R2 > 0.96 for all compounds). Photosystem II efficiency Photosystem II (PSII) efficiency was determined measuring chlorophyll a fluorescence with a fluorimeter (Hansatech FMS2, Hansatech Instruments Ltd, Norfolk, UK), after 2, 7 and 16 days since the start of the experiment, independently in apical, median and basal leaves. Maximum quantum efficiency of PSII was determined as Fv/Fm, where Fv is the variable fluorescence, calculated as the difference between maximum fluorescence (Fm, measured after application of a saturating light pulse (8000 μmol (photon) m−2 s−1; 700 ms)) and minimum fluorescence yield in dark-adapted state (F0). Non-photochemical quenching (NPQ = (Fm – Fm′)/Fm′, where Fm′ is the maximum fluorescence yield under ambient light regime), and electron transport rate (ETR = PAR * 0.5 * ΦPSII * 0.84, where ΦPSII is the quantum efficiency of PSII) were also calculated. Zinc, Na and dodecyl sulfate extraction and quantification For each organ (leaves, stem and roots) Zn and Na concentration were determined after digestion of 0.2 g DW of plant material in concentrated nitric acid (HNO3) by flame atomic absorption spectrophotometry (model 373, PerkinElmer, Norwalk, CT, USA). Two analytical reference standards of Zn and Na were used as a control (WEPAL IPE, Wageningen University): leaf of Daucus carota L. (25.0 ± 2.93 mg kg−1 of Zn, 10,600 ± 1010 mg kg−1 of Na, certified concentrations) and shoot of D. carota (185.0 ± 16.4 mg kg−1 of Zn, 852.0 ± 126.7 mg kg−1 of Na, certified concentrations). In addition, dodecyl sulfate content was investigated at the end of treatment in each organ by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Briefly, 0.5 g FW material were finely ground in liquid nitrogen with 1.5 ml of methanol 70% v/v. The extracts were centrifuged at 17,000g for 5 min. After centrifugation, the supernatant was filtered with 0.25 μm syringe filters (Sartorius Stedim biotech GmbH, Goettingen, Germany) and stored at −20 °C until LC–MS/MS analysis. The extracts were analyzed by LC–MS/MS in Multiple Reaction Monitoring mode using a PE Sciex API 365 triple quadrupole mass spectrometer (Concord, ON, Canada) equipped with an atmospheric pressure chemical ionization source and coupled to a Agilent 1100 HPLC system with binary pump and auto-sampler. Chromatographic separation was performed by a Phenomenex Curosil PFP 2 × 50 5 μm column (Phenomenex, Torrance, CA, USA). The elution was carried out in gradient mode using acetonitrile 0.1% formic acid (solvent A); 0.1% formic acid (solvent B). The gradient elution was programmed as follows: 0.0–3.0 min, A 25%; 3.0–8.0 min, A 25–95%; 8.0–14.0 min, A 95%; followed by 4 min equilibration time (A 25%). Other chromatographic conditions were: flow rate 400 μl min−1, injection volume 20 μl and temperature 20 °C. The MS/MS experiments were performed in Electrospray negative ion mode using nitrogen as collision gas, with the following operation parameters: source type, Turbospray; nebulizer gas 9 (arbitrary units); curtain gas 8 (arbitrary units); temperature 550 °C; Ionspray Voltage −3500 V, entrance potential 10 V, declustering potential −35 V; focusing potential −215 V; collision cell entrance potential −7.99 V. The parent ion-precursor ion transitions monitored were 265.1–79.8 m/z (collision energy −95 V, collision cell exit potential −6.70 V) and 265.1–96.8 m/z (collision energy −34 V, collision cell exit potential −8.50 V). Dodecyl sulfate (Sigma-Aldrich, Darmstadt, Germany) calibration curve was built (R2 = 0.901). Data were normalized according to matrix effect and recovery percentage, measured independently for roots, stem and leaves. Matrix effect was calculated as peak area of the sample spiked after extraction/peak area of the standard, while recovery was calculated as peak area of the sample spiked before extraction/peak area of the sample spiked after extraction. Statistical analysis Data were subjected to two-way ANOVA (P ≤ 0.05) and letters are attributed to treatments according to Tukey–Kramer test, when interaction between factors SDS and Zn resulted significant (P < 0.05). One-tailed t-test analysis (P < 0.05) between 1 mM Zn and 1 mM Zn + 0.5 mM SDS treatments was performed in basal leaves and roots in order to highlight differences in Zn translocation as a consequence of SDS co-exposure. All statistical analyses for physicochemical parameters, in fresh and dried material, were done by using NCSS 2004 Statistical Analysis System Software. Results Dodecyl sulfate and Zn uptake Dodecyl sulfate root absorption and translocation to leaves was detected in 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS plants (Figure 1). Moreover, the high sensitivity of LC-MS/MS analyses revealed traces of dodecyl sulfate also in control and 1 mM Zn-treated samples (Figure 1), proving the ubiquity and persistence of detergents such as SDS. However, dodecyl sulfate concentrations in all organs of Villafranca clone were significantly increased in plants treated with 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS (Figure 1, factor SDS P ≤ 0.05). In particular, roots were the organ where dodecyl sulfate was mainly retained, and an accumulation up to 4 mg g−1 FW (corresponding to 36 mg g−1 DW) was detected in roots of SDS-treated plants. Figure 1. View largeDownload slide Dodecyl sulfate concentration in P. alba Villafranca organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 3). Bars represent mean + SD. *P < 0.05, **P < 0.01, ***P < 0.001, ns = not significant. Figure 1. View largeDownload slide Dodecyl sulfate concentration in P. alba Villafranca organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 3). Bars represent mean + SD. *P < 0.05, **P < 0.01, ***P < 0.001, ns = not significant. Analysis of Zn content provided evidence of Villafranca as a root accumulator clone, reaching concentrations up to 1.1 mg g−1 DW in roots of 1 mM Zn-treated poplar plants (Figure 2). Figure 2. View largeDownload slide Zinc concentrations in P. alba Villafranca clone organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 4). Bars represent mean + SD. *P < 0.05, ***P < 0.001, ns = not significant. Figure 2. View largeDownload slide Zinc concentrations in P. alba Villafranca clone organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 4). Bars represent mean + SD. *P < 0.05, ***P < 0.001, ns = not significant. Although SDS co-exposure did not enhance significantly the total Zn absorption by poplar plants (P = 0.23), a general increasing trend of Zn uptake under SDS treatments was observed at leaf level, and one-tailed t-test analysis between 1 mM Zn and 1 mM Zn + 0.5 mM SDS treated plants revealed a significant (P = 0.03) increase in Zn concentration in basal leaves together with a decrease (P = 0.05) in Zn concentration in roots of the cross-stressed plants, proving the ability of SDS to improve Zn translocation from roots to leaves (Figure 2). Phenotyping Presence of SDS alone as well as the simultaneous presence of the surfactant and the heavy metal Zn induced in basal leaves wide necrosis areas, which expanded acropetally and finally led to the loss of the most damaged leaves (−25% leaves in 1 mM Zn + 0.5 mM SDS treated plants and −13% leaves in 0.5 mM SDS treated plants, compared with control, after 21 days of treatment) (Figure 3). Figure 3. View largeDownload slide Dynamics of leaves abscission of P. alba Villafranca clone (n = 5) during the treatment period with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution (1 μM Zn). Figure 3. View largeDownload slide Dynamics of leaves abscission of P. alba Villafranca clone (n = 5) during the treatment period with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution (1 μM Zn). In particular, after 21 days of treatment with 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS, plants showed a decrease in fresh (−28.9% and −34.9%) and dry (−22.4% and −29.0%) leaves biomass in comparison with control plants, but the interaction between the two main factors remained not significant (Table 1). Leaves growth in terms of RGRl was also reduced (−12% in both 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS treated plants) but the only significant interaction between Zn and SDS factors was observed for RGRr, which was significantly reduced in 1 mM Zn-treated plants (−50%) (Table 1). Table 1. Physiological growth traits of P. alba Villafranca clone treated with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution after 21 days of treatment. Relative growth rate was calculated for leaves (RGRl), stem (RGRs), roots (RGRr) and for the whole plant (RGRtot). In each row, statistical significance was determined with two-way ANOVA. Different letters next to the numbers represent statistical difference according to Tukey–Kramer test (n = 5); no letters are placed when interaction amongst Zn and SDS factors was not significant. *P < 0.05, **P < 0.01, ***P < 0.001, ns = not significant.   Treatment  ANOVA  Control  Zn  SDS  SDS + Zn  Zn  SDS  SDS × Zn    Stem length (cm)  59.2 ± 3.9  60.4 ± 6.7  57.7 ± 5.0  57.2 ± 2.7  ns  ns  ns  Leaves (n)  30.0 ± 2.0  28.4 ± 2.3  26.2 ± 4.4  22.4 ± 1.9  ns  **  ns  FW (g)1  Leaves  15.0 ± 1.5  14.8 ± 2.1  10.7 ± 1.9  9.8 ± 1.5  ns  ***  ns  Stem  8.4 ± 1.8  9.8 ± 1.8  7.7 ± 1.2  7.7 ± 1.1  ns  ns  ns  Roots  9.8 ± 0.8  9.2 ± 2.1  9.3 ± 1.4  8.5 ± 1.4  ns  ns  ns  Total  33.3 ± 2.9  33.3 ± 5.8  27.7 ± 4.1  26.0 ± 3.4  ns  **  ns  DW (g)2  Leaves  3.1 ± 0.3  3.1 ± 0.6  2.4 ± 0.5  2.2 ± 0.4  ns  **  ns  Stem  1.6 ± 0.4  1.9 ± 0.6  1.6 ± 0.3  1.6 ± 0.3  ns  ns  ns  Roots  0.6 ± 0.2  0.7 ± 0.2  0.7 ± 0.1  0.8 ± 0.1  ns  ns  ns  Total  5.3 ± 0.8  5.7 ± 1.3  4.7 ± 0.8  4.6 ± 0.7  ns  ns  ns    LMR3  0.59 ± 0.06  0.55 ± 0.04  0.51 ± 0.04  0.48 ± 0.03  ns  **  ns  SMR4  0.29 ± 0.04  0.32 ± 0.03  0.33 ± 0.02  0.35 ± 0.03  ns  *  ns  RMR5  0.11 ± 0.03  0.13 ± 0.02  0.16 ± 0.04  0.17 ± 0.03  ns  *  ns  RGRtot  0.12 ± 0.01  0.12 ± 0.01  0.12 ± 0.01  0.11 ± 0.01  ns  ns  ns  RGRl  0.08 ± 0.01  0.08 ± 0.02  0.07 ± 0.01  0.07 ± 0.02  ns  **  ns  RGRs  0.09 ± 0.02  0.09 ± 0.01  0.09 ± 0.01  0.09 ± 0.02  ns  ns  ns  RGRr  0.06 ± 0.02 a  0.03 ± 0.01 b  0.07 ± 0.01 a  0.08 ± 0.01 a  **  ***  **    Treatment  ANOVA  Control  Zn  SDS  SDS + Zn  Zn  SDS  SDS × Zn    Stem length (cm)  59.2 ± 3.9  60.4 ± 6.7  57.7 ± 5.0  57.2 ± 2.7  ns  ns  ns  Leaves (n)  30.0 ± 2.0  28.4 ± 2.3  26.2 ± 4.4  22.4 ± 1.9  ns  **  ns  FW (g)1  Leaves  15.0 ± 1.5  14.8 ± 2.1  10.7 ± 1.9  9.8 ± 1.5  ns  ***  ns  Stem  8.4 ± 1.8  9.8 ± 1.8  7.7 ± 1.2  7.7 ± 1.1  ns  ns  ns  Roots  9.8 ± 0.8  9.2 ± 2.1  9.3 ± 1.4  8.5 ± 1.4  ns  ns  ns  Total  33.3 ± 2.9  33.3 ± 5.8  27.7 ± 4.1  26.0 ± 3.4  ns  **  ns  DW (g)2  Leaves  3.1 ± 0.3  3.1 ± 0.6  2.4 ± 0.5  2.2 ± 0.4  ns  **  ns  Stem  1.6 ± 0.4  1.9 ± 0.6  1.6 ± 0.3  1.6 ± 0.3  ns  ns  ns  Roots  0.6 ± 0.2  0.7 ± 0.2  0.7 ± 0.1  0.8 ± 0.1  ns  ns  ns  Total  5.3 ± 0.8  5.7 ± 1.3  4.7 ± 0.8  4.6 ± 0.7  ns  ns  ns    LMR3  0.59 ± 0.06  0.55 ± 0.04  0.51 ± 0.04  0.48 ± 0.03  ns  **  ns  SMR4  0.29 ± 0.04  0.32 ± 0.03  0.33 ± 0.02  0.35 ± 0.03  ns  *  ns  RMR5  0.11 ± 0.03  0.13 ± 0.02  0.16 ± 0.04  0.17 ± 0.03  ns  *  ns  RGRtot  0.12 ± 0.01  0.12 ± 0.01  0.12 ± 0.01  0.11 ± 0.01  ns  ns  ns  RGRl  0.08 ± 0.01  0.08 ± 0.02  0.07 ± 0.01  0.07 ± 0.02  ns  **  ns  RGRs  0.09 ± 0.02  0.09 ± 0.01  0.09 ± 0.01  0.09 ± 0.02  ns  ns  ns  RGRr  0.06 ± 0.02 a  0.03 ± 0.01 b  0.07 ± 0.01 a  0.08 ± 0.01 a  **  ***  **  1Fresh weight. 2Dry weight. 3Leaves mass ratio. 4Stem mass ratio. 5Root mass ratio. Sodium content In order to understand the reason for the extensive foliar necrosis starting from older leaves, and subsequent leaf abscission observed in poplar plants treated with 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS (Figure 3), the possibility of having introduced a multiple stress factor during the experimental trial with surfactant SDS was explored, since SDS has the ability to rapidly dissociate in aqueous solution in Na+ and dodecyl sulfate–. Therefore, the organ content of Na was also investigated (Figure 4). Figure 4. View largeDownload slide Sodium concentrations in P. alba Villafranca clone organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 4). Bars represent mean + SD. *P < 0.05, ***P < 0.001, ns = not significant. Figure 4. View largeDownload slide Sodium concentrations in P. alba Villafranca clone organs after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA inside each organ; different letters represent statistical difference according to Tukey–Kramer test (P < 0.05; n = 4). Bars represent mean + SD. *P < 0.05, ***P < 0.001, ns = not significant. While dodecyl sulfate and Zn were found to be mainly accumulated in roots, stem was the organ where the highest Na concentration was found, in both 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS treatments, reaching up to 1 mg g−1 DW in stem of 0.5 mM SDS-treated plants (Figure 4). A significant accumulation of Na (factor SDS, P < 0.001) was observed in median and basal leaves of 0.5 mM SDS and 1 mM Zn + 0.5 mM SDS treated plants. Looking for the relationship between Na and dodecyl sulfate, we found that these two components were directly correlated in leaves (Figure 5). In fact, in basal, median and apical leaves the increased accumulation of dodecyl sulfate was significantly related to Na accumulation (P < 0.0001, R2 = 0.6322). Figure 5. View largeDownload slide Correlation among data (n = 34) of dodecyl sulfate concentration (mg g–1 FW) and Na concentration (mg g–1 DW) in basal, median and apical leaves of P. alba Villafranca clone after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Results were analyzed by linear regression analyses. Figure 5. View largeDownload slide Correlation among data (n = 34) of dodecyl sulfate concentration (mg g–1 FW) and Na concentration (mg g–1 DW) in basal, median and apical leaves of P. alba Villafranca clone after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Results were analyzed by linear regression analyses. Photosynthetic pigments content and PSII efficiency Since one of most common target site of plant stress is the photosynthetic apparatus, leaves were investigated with HPLC analyses to determine possible variations on photosynthetic pigments content, able to interfere with plant health status. Apical and median leaves revealed no differences in lutein, chlorophyll a and b, and β-carotene contents between control and treated plants (see Figure S1 available as Supplementary Data at Tree Physiology Online). On the contrary, basal leaves (Figure 6) that remained intact after 21 days of treatment showed a statistically significant increase of lutein (+52.9%), chlorophyll a (+48.4%) and β-carotene (+66.4%) in 1 mM Zn-treated plants compared with control. Regarding treatments with only SDS, and the cross-stress treatment, no effects on photosynthetic pigment content were observed compared with control data (Figure 6). Figure 6. View largeDownload slide Photosynthetic pigments concentrations in basal leaves of P. alba Villafranca clone after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA followed by Tukey–Kramer test (P < 0.05; n = 5). Bars represent mean + SD. ***P < 0.001, ns = not significant. Figure 6. View largeDownload slide Photosynthetic pigments concentrations in basal leaves of P. alba Villafranca clone after 21 days of treatment with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. Statistical significance was determined with two-way ANOVA followed by Tukey–Kramer test (P < 0.05; n = 5). Bars represent mean + SD. ***P < 0.001, ns = not significant. Monitoring of PSII efficiency is a powerful tool for studying plant performance under biotic and abiotic stress, since it is able to perceive the photosynthetic damage before visible symptoms appear. Chlorophyll a fluorescence analyses confirmed the healthy status of apical leaves that did not show SDS-related damage, while in median leaves an increase of NPQ occurred, warning of photosynthetic impairment before necrosis appearance (see Figure S2 available as Supplementary Data at Tree Physiology Online). On the contrary, in basal leaves monitored during the development of necrosis but still remaining attached to plants, it was evident that PSII efficiency was the parameter most affected by SDS treatment (Figure 7) (P-values are available in Table S1 available as Supplementary Data at Tree Physiology Online). Figure 7. View largeDownload slide Fv/Fm (A), ETR (B) and NPQ (C) measurements in basal leaves of P. alba measured at 2, 7 and 16 days of exposure before abscission. Plants were treated with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. At each sampling time statistical significance was determined with two-way ANOVA followed by Tukey–Kramer test (P < 0.05; n = 3). Data represent mean ± SE. Figure 7. View largeDownload slide Fv/Fm (A), ETR (B) and NPQ (C) measurements in basal leaves of P. alba measured at 2, 7 and 16 days of exposure before abscission. Plants were treated with 1 mM Zn, 0.5 mM SDS, 1 mM Zn + 0.5 mM SDS and control Hoagland solution. At each sampling time statistical significance was determined with two-way ANOVA followed by Tukey–Kramer test (P < 0.05; n = 3). Data represent mean ± SE. Decrease of Fv/Fm and ETR performance, together with an increase in NPQ, was observed as a consequence of exposure to factor SDS already after 2 days of treatment in 0.5 mM SDS-treated plants, when expansion of necrosis areas started to occur, while in 1 mM Zn + 0.5 mM SDS plants, PSII efficiency started to be compromised only after 16 days of treatment. Discussion Environmental contamination by surfactants occurs due to their presence in domestic waste water caused by detergents used for all categories of washing. Their diffusion is also due to the wide use in textiles, fibers, paints and the paper industry as reported by several authors (Cserháti et al. 2002, Ojo and Oso 2009, Margot et al. 2015). The presence of dodecyl sulfate traces found in control and 1 mM Zn-treated plants pots, although the substrate and hydroponic equipment have been washed carefully with deionized water, prove that SDS is a widespread contaminant and for this reason is suitable to be used as a model surfactant in toxicological testing (Cserháti et al. 2002). Other sources of anionic surfactant contamination derive from the use of SDS during phytoremediation practices, in order to improve the capability of plants to uptake heavy metal contaminants. The effective increase of plant absorption of heavy metals as a consequence of co-exposure with surfactants is anyway controversial. Sodium dodecyl sulfate has been observed to increase the dry biomass of Althaea rosea Cav., promoting Cd accumulation in shoots and roots (Liu et al. 2009). In A. rosea and Calendula officinalis L. SDS-enhanced uptake of Cd was demonstrated (Liu et al. 2008, 2009). Almeida et al. (2009) reported an enhanced Cu accumulation in plant roots but not increased Cu translocation, indicating that surfactants may favor Cu adsorption to the roots (phytostabilization) in Halimione portulacoides L. Research on water hyacinth (Eichhornia crassipes (Mart.) Solms) is, on the contrary, indicative of a negative effect caused by SDS on metal uptake from waste water (Muramoto and Oki 1984). In P. alba clone the co-exposure of SDS and Zn induces Zn translocation towards basal leaves without really changing the Zn uptake in the plant. Moreover, roots were the organ that accumulated Zn at the highest concentration, confirming results previously obtained in Villafranca clone (Romeo et al. 2014, Ariani et al. 2016) and provide evidence that the dynamics of Zn accumulation in this clone remain similar in the presence of SDS. This information is indicative as the dynamic of SDS/heavy metal uptake is very different among plants. Furthermore, several processes occur in plants during phytoremediation practices and the interaction between factors of stress is poorly studied; research in this topic was done focusing attention on plants' ability to accumulate one or more heavy metal without taking into account the co-factor of stress induced by SDS use. The capability of plants to take up SDS is demonstred in Hedera helix L. by Marešová et al. (2009) while Dirilgen and Ince (1995) reported plant uptake of SDS in fronds of floating aquatic macrophytes Lemna minor L., finding that there is a positive correlation between the concentration of this detergent in the growth media and its accumulation in plant organs. Dodecyl sulfate accumulation in roots, as well as its translocation to leaves in P. alba Villafranca clone, prove the ability of poplar to uptake this surfactant as also observed for other molecules coming from the emerging class of micro-pollutants like caffeine and erythromycin (Pierattini et al. 2016a, 2016b). A more detailed study is required to explain the influence of SDS on mechanisms of metal uptake and distribution in poplar organs, as well as its influence on root surface. Sodium dodecyl sulfate is known to be extremely effective in the solubilization of membrane proteins; moreover, the ability of SDS micelles to bind Zn2+ ions has been demonstrated (Talens-Alesson 2007). Both characteristics can improve metal mobility in the lipophilic structures and could explain the fact that SDS increases the translocation towards to the leaves, improving Zn mobilization inside the plant. The present research provides evidence on the introduction of a multiple stress factor during an experimental trial with surfactant SDS, represented by the ion Na. This ion is released by the SDS molecule and could contribute to the physiological disorder observed in poplar plants. The accumulation of Na observed in basal leaves may hint to a role of this ion in foliar necrosis, which needs further investigation. It has been observed that P. alba response to salt stress varies significantly according to the genotype (Mao et al. 2008, Beritognolo et al. 2011). Li et al. (2016) reported that male clones have better performances during salt stress compared with female clones in Populus deltoides W. Bartram ex Humphry Marshall. Since P. alba L. Villafranca is a female clone, this could have enhanced its sensitivity to Na and dodecyl sulfate stress. Moreover, the preferential accumulation of Na in stem observed also in Populus × canescens (Aiton) Sm. under salt stress (Escalante-Pérez et al. 2009) may suggest a role of this organ as a ‘buffer-organ’ in poplar. As regards photosynthetic pigments, an increase of chlorophylls and carotenoids content under Zn exposure was observed also in willow plants treated with up to 2.5 mM Zn (Borowiak et al. 2015) and in Phyllostachys pubescens (Pradelle) Mazel ex J. Houz (Peng et al. 2015), and also in Villafranca clone under similar growth conditions and Zn stress (Romeo et al. 2014). It is revealed that there is some positive influence of Zn on Villafranca clone growth at 65 ppm of Zn concentration (1 mM). In particular, it seems that plants were able to defend and protect their photosynthetic pigment integrity against Zn stress. It has been described by Forni et al. (2008) that chlorophyll pigments content of the aquatic macrophytes Azolla filiculoides Lam. and L. minor decrease under SDS exposure; in our trial, when poplar plants were exposed to both Zn and SDS, and SDS alone, no differences in photosynthetic pigment content were observed compared with control, confirming the ability of the poplar Villafranca clone to tolerate different types of pollutants. Impairment of PSII photosynthetic performance in terms of Fv/Fm and ETR decrease is frequently described as a consequence of abiotic stress. The reduced efficiency of PSII consequent to SDS exposure could be a result of Na and dodecyl sulfate damage to the photosynthetic apparatus. Under Na stress, decrease of ETR and increase of NPQ have been observed in tomato plants, although the maximum quantum efficiency of PSII photochemistry (Fv/Fm) remained unvaried throughout time and treatments (Zribi et al. 2009). Similar necrosis areas and leaf abscission were recorded also in leaves under 1 mM Zn + 0.5 mM SDS, but the effect of this treatment on PSII apparatus seems less invasive, maybe because of the presence of Zn, which could develop a role on Na and dodecyl sulfate stress alleviation. In conclusion, although P. alba Villafranca clone is actually considered able to preserve healthy traits of resistance under relatively high pollutants concentrations, both heavy metals and organic micro-pollutants, this research demonstrates that SDS induces physiological imbalance and results in foliar damage. Moreover, we demonstrated that poplar plants are able to absorb and accumulate this detergent, and that co-treatment with SDS and Zn did not increase total uptake of this heavy metal but enhanced its translocation among plant organs. Eventual toxic effects due to detergents exposure should be taken into account when performing surfactant-enhanced phytoremediation trials. Moreover, additional trials with Na are needed to state the role of this ion in Villafranca leaf necrosis and abscission, and a deeper investigation on SDS plant metabolites production, and their characterization, must be performed. Supplementary Data Supplementary Data for this article are available at Tree Physiology Online. Conflict of interest None declared. Funding Agrobioscience PhD program at Scuola Superiore Sant’Anna of Pisa granted a scholarship to E.C.P. This research was supported by Institute of Life Sciences, Scuola Superiore Sant’Anna, Pisa, grant. Acknowledgments We would like to thank Dr Gaia Monteforti for sharing her expertize in atomic absorption spectrophotometry. References Almansoory AF, Hasan HA, Idris M, Abdullah SRS, Anuar N ( 2015) Potential application of a biosurfactant in phytoremediation technology for treatment of gasoline-contaminated soil. Ecol Eng  84: 113– 120. Google Scholar CrossRef Search ADS   Almeida CMR, Dias AC, Mucha AP, Bordalo AA, Vasconcelos MTSD ( 2009) Influence of surfactants on the Cu phytoremediation potential of a salt marsh plant. Chemosphere  75: 135– 140. Google Scholar CrossRef Search ADS PubMed  Anderberg EK, Artursson P ( 1993) Epithelial transport of drugs in cell culture. VIII: effects of sodium dodecyl sulfate on cell membrane and tight junction permeability in human intestinal epithelial (Caco-2) cells. J Pharm Sci  82: 392– 398. Google Scholar CrossRef Search ADS PubMed  Ariani A, Francini A, Andreucci A, Sebastiani L ( 2016) Over-expression of AQUA1 in Populus alba Villafranca clone increases relative growth rate and water use efficiency, under Zn excess condition. Plant Cell Rep  35: 289– 301. Google Scholar CrossRef Search ADS PubMed  Arnon DI, Hoagland DR ( 1940) Crop production in artificial culture solutions and in soils with special reference to factors influencing yields and absorption of inorganic nutrients. Soil Sci  50: 463– 485. Benáková M, Ahmadi H, Dučaiová Z, Tylová E, Clemens S, Tůma J ( 2017) Effects of Cd and Zn on physiological and anatomical properties of hydroponically grown Brassica napus plants. Environ Sci Pollut Res  24: 20705– 20716. Google Scholar CrossRef Search ADS   Beritognolo I, Harfouche A, Brilli F et al.  . ( 2011) Comparative study of transcriptional and physiological responses to salinity stress in two contrasting Populus alba L. genotypes. Tree Physiol  31: 1335– 1355. Google Scholar CrossRef Search ADS PubMed  Borowiak K, Gąsecka M, Mleczeck M, Dąbrowski J, Chadzinikolau T, Magdziak Z, Golin´ski P, Rutkowski P, Kozubik T ( 2015) Photosynthetic activity in relation to chlorophylls, carbohydrates, phenolics and growth of a hybrid Salix purpurea x triandra x viminalis 2 at various Zn concentrations. Acta Physiol Plant  37: 155– 167. Google Scholar CrossRef Search ADS   Chaney RL ( 1993) Zinc phytotoxicity. In: Robson AD (ed) Zinc in soil and plants . Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 135– 150. Google Scholar CrossRef Search ADS   Chaturvedi V, Kumar A ( 2011) Diversity of culturable sodium dodecyl sulfate (SDS) degrading bacteria isolated from detergent contaminated ponds situated in Varanasi city, India. Int Biodeterior Biodegrad  65: 961– 971. Google Scholar CrossRef Search ADS   Cserháti T, Forgács E, Oros G ( 2002) Biological activity and environmental impact of anionic surfactants. Environ Int  28: 337– 348. Google Scholar CrossRef Search ADS PubMed  Di Baccio D, Tognetti R, Sebastiani L, Vitagliano C ( 2003) Responses of Populus deltoides × Populus nigra (Populus × euramericana) clone I-214 to high zinc concentrations. New Phytol  159: 443– 452. Google Scholar CrossRef Search ADS   Di Baccio D, Tognetti R, Minnocci A, Sebastiani L ( 2009) Responses of the Populus × euramericana clone I-214 to excess zinc: Carbon assimilation, structural modifications, metal distribution and cellular localization. Environ Exp Bot  67: 153– 163. Google Scholar CrossRef Search ADS   Dickmann DI ( 1971) Photosynthesis and respiration by developing leaves of Cottonwood (Populus deltoides Bartr.). Bot Gaz  132: 253– 259. Google Scholar CrossRef Search ADS   Dirilgen N, Ince N ( 1995) Inhibition effect of the anionic surfactant SDS on duckweed, Lemna minor with considerations of growth and accumulation. Chemosphere  3: 4185– 4196. Google Scholar CrossRef Search ADS   Escalante-Pérez M, Lautner S, Nehls U et al.  . ( 2009) Salt stress affects xylem differentiation of grey poplar (Populus x canescens). Planta  229: 299– 309. Google Scholar CrossRef Search ADS PubMed  Forni C, Giordani F, Pintore M, Campanella L ( 2008) Effects of sodium dodecyl sulphate on the aquatic macrophytes Azolla and Lemna. Plant Biosyst  142/3: 665– 668. Google Scholar CrossRef Search ADS   Forni C, Braglia R, Harren FJM, Cristescu SM ( 2012) Stress responses of duckweed (Lemna minor L.) and water velvet (Azolla filiculoides Lam.) to anionic surfactant sodium-dodecyl-sulfate (SDS). Aquat Toxicol  110–111: 107– 113. Google Scholar CrossRef Search ADS PubMed  Kumar S, Kirha TJ, Thonger T ( 2014) Toxicological effects of sodium dodecyl sulfate. J Chem Pharm Res  6: 1488– 1492. Li Y, Duan B, Chen J, Korpelainen H, Niinemets Ü, Li C ( 2016) Males exhibit competitive advantages over females of Populus deltoides under salinity stress. Tree Physiol  36: 1573– 1584. Google Scholar CrossRef Search ADS PubMed  Liu JN, Zhou QX, Sun T, Ma LQ, Wang S ( 2008) Identification and chemical enhancement of two ornamental plants for phytoremediation. Bull Environ Contam Toxicol  80: 260– 265. Google Scholar CrossRef Search ADS PubMed  Liu JN, Zhou QX, Sun T ( 2009) Cadmium tolerance and accumulation of Althaea rosea Cav. and its potential as a hyperaccumulator under chemical enhancement. Environ Monit Assess  149: 419– 427. Google Scholar CrossRef Search ADS PubMed  Lloyd GB, McCown BH ( 1980) Commercially feasible micropropagation of mountain laurel, Kalmia latifolia, by use of shoot-tip culture. Comb Proc Int Plant Prop Soc  30: 421– 427. Mao HP, Iwanaga F, Yamanaka N, Yamamoto F ( 2008) Growth, photosynthesis, and ion distribution in hydroponically cultured Populus alba L. cuttings grown under various salinity concentrations. Landsc Ecol Eng  4: 75– 82. Google Scholar CrossRef Search ADS   Mao X, Jiang R, Xiao W, Yu J ( 2015) Use of surfactants for the remediation of contaminated soils: a review. J Hazard Mater  285: 419– 435. Google Scholar CrossRef Search ADS PubMed  Marešová J, Hornìk M, Pipìška M, Augustin J ( 2009) Influence of anionic surfactants on Zn2+ and Sr2+ uptake by ivy (Hedera helix L.) leaves. Nova Biotechnol  9: 333– 339. Margot J, Rossi L, Barry DA, Holliger C ( 2015) A review of the fate of micropollutants in wastewater treatment plants. WIREs Water  2: 457– 487. Google Scholar CrossRef Search ADS   Marmiroli M, Pietrini F, Maestri E, Zacchini M, Marmiroli N, Massacci A ( 2011) Growth, physiological and molecular traits in Salicaceae trees investigated for phytoremediation of heavy metals and organics. Tree Physiol  31: 1319– 1334. Google Scholar CrossRef Search ADS PubMed  Messina CM, Faggio C, Laudicella VA, Sanfilippo M, Trischitta F, Santulli A ( 2014) Effect of sodium dodecyl sulfate (SDS) on stress response in the Mediterranean mussel (Mytilus galloprovincialis): regulatory volume decrease (Rvd) and modulation of biochemical markers related to oxidative stress. Aquat Toxicol  157: 94– 100. Google Scholar CrossRef Search ADS PubMed  Muramoto S, Oki Y ( 1984) Influence of anionic surface-active agents on the uptake of heavy metals by water hyacinth (Eichhornia crassipes). Bull Environ Contam Toxicol  33: 444– 450. Google Scholar CrossRef Search ADS PubMed  Nguyen HM, Phan CM, Sen T ( 2016) Degradation of sodium dodecyl sulfate by photoelectrochemical and electrochemical processes. Chem Eng J  287: 633– 639. Google Scholar CrossRef Search ADS   Ojo OA, Oso BA ( 2009) Isolation of pasmid-DNA from synthetic detergent degraders in wastewater from a tropical environment. Afr J Microbiol Res  3: 123– 127. Pandey P, Gopal G ( 2010) Effect of detergents on the growth of two aquatic plants: Azolla pinnata and Hydrilla verticillata. Environ We Int J Sci Tech  5: 107– 114. Paulo AMS, Plugge CM, García-Encina PA, Stams AJM ( 2013) Anaerobic degradation of sodium dodecyl sulfate (SDS) by denitrifying bacteria. Int Biodeterior Biodegrad  84: 14– 20. Google Scholar CrossRef Search ADS   Peng D, Shafi M, Wang Y, Li S, Yan W, Chen J, Ye Z, Liu D ( 2015) Effect of Zn stresses on physiology, growth, Zn accumulation, and chlorophyll of Phyllostachys pubescens. Environ Sci Pollut Res  22: 14983– 14992. Google Scholar CrossRef Search ADS   Pettersson A, Adamsson M, Dave G ( 2000) Toxicity and detoxification of Swedish detergents and softener products. Chemosphere  41: 1611– 1620. Google Scholar CrossRef Search ADS PubMed  Pierattini EC, Francini A, Raffaelli A, Sebastiani L ( 2016a) Degradation of exogenous caffeine by Populus alba and its effects on endogenous caffeine metabolism. Environ Sci Pollut Res  23: 7298– 7307. Google Scholar CrossRef Search ADS   Pierattini EC, Francini A, Raffaelli A, Sebastiani L ( 2016b) Morpho-physiological response of Populus alba to erythromycin: a timeline of the health status of the plant. Sci Total Environ  569–570: 540– 547. Google Scholar CrossRef Search ADS PubMed  Pilipović A, Orlović S, Rončević S, Nikolić N, Župunski M, Spasojević J ( 2015) Results of selection of poplars and willows for water and sediment phytoremediation. Agric Forestry  61: 205– 211. Ramamurthy A, Schalchian H ( 2013) Surfactant assisted removal of Cu(II), Cd(II) and Pb(II) from contaminated soils. Environ Prot Eng  39: 87– 99. Romeo S, Francini A, Ariani A, Sebastiani L ( 2014) Phytoremediation of Zn: identify the diverging resistance, uptake and biomass production behaviours of poplar clones under high zinc stress. Water Air Soil Poll  225: 1813– 1819. Google Scholar CrossRef Search ADS   Sebastiani L, Scebba F, Tognetti R ( 2004) Heavy metal accumulation and growth responses in poplar clones Eridano (Populus deltoides x maximowiczii) and I-214 (P. x euramericana) exposed to industrial waste. Environ Exp Bot  52: 79– 88. Google Scholar CrossRef Search ADS   Subba P, Mukhopadhyay M, Mahato SK, Bhutia KD, Mondal TK, Ghosh SK ( 2014) Zinc stress induces physiological, ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings. Physiol Mol Biol Plants  20: 461– 473. Google Scholar CrossRef Search ADS PubMed  Talens-Alesson FI ( 2007) Behaviour of SDS micelles bound to mixtures of divalent and trivalent cations during ultrafiltration. Colloid Surface A  299: 169– 179. Google Scholar CrossRef Search ADS   Todeschini V, Lingua G, D’Agostino G, Carniato F, Roccotiello E, Berta G ( 2011) Effects of high zinc concentration on poplar leaves: a morphological and biochemical study. Environ Exp Bot  71: 50– 56. Google Scholar CrossRef Search ADS   Torres LG, Climent M, Saquelares J, Bandala ER, Urquiza J, Iturbe R ( 2007) Characterization and treatability of a contaminated soil from an oil exploration zone. Int J Environ Sci Technol  4: 311– 322. Google Scholar CrossRef Search ADS   Wang J, Wang J, Xu C, Liu R, Chen Y ( 2016) Molecular mechanism of catalase activity change under sodium dodecyl sulfate-induced oxidative stress in the mouse primary hepatocytes†. J Hazard Mater  307: 173– 183. Google Scholar CrossRef Search ADS PubMed  Zribi L, Fatma G, Fatma R, Salwa R, Hassan N, Néjib RM ( 2009) Application of chlorophyll fluorescence for the diagnosis of salt stress in tomato ‘Solanum lycopersicum (variety Rio Grande)’. Sci Hortic  120: 367– 372. Google Scholar CrossRef Search ADS   Author notes handling Editor Joào Pereira © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com
TI - Surfactant and heavy metal interaction in poplar: a focus on SDS and Zn uptake
JF - Tree Physiology
DO - 10.1093/treephys/tpx155
DA - 2017-12-07
UR - https://www.deepdyve.com/lp/oxford-university-press/surfactant-and-heavy-metal-interaction-in-poplar-a-focus-on-sds-and-zn-D9Esii6tH2
SP - 109
EP - 118
VL - 38
IS - 1
DP - DeepDyve
ER -