Coupling phytoremediation efficiency and detoxification to assess the role of P in the Cu tolerant Ricinus communis L.

Phosphorous (P) fertilization is an important agronomic practice, but its role in enhancing phytoremediation efficacy and mediating detoxification has rarely been reported in environmental remediation studies. In this study, a pot experiment was undertaken to assess: firstly, the effect of P on phytoextraction of Cu by Ricinus communis L.; secondly, the potential mechanisms by differentiating the effects of the plant from that of P fertilizer (Ca(H2PO4)2); and thirdly, the role of P in physiological detoxification. Results showed that the application of P fertilizer significantly (p ≤ 0.05) increased the plant biomass as well as the Cu concentrations in plant tissues. This enhanced the phytoremediation efficiency represented by the total Cu extraction (up to 121.3 µg Cu plant-1). Phosphorous (P) fertilizer led to a negligible decline in soil pH (0.2 units) but significantly (p ≤ 0.05) reduced the concentrations of soil available in Cu and Fe, due to the formation of insoluble Cu/Fe-phosphate precipitates. Nevertheless, P fertilizer still improved the accumulation and extraction of Cu by R. communis, most likely attributable to the Fe-deficiency induced by applied P fertilizer. Moreover, the application of P fertilizer revealed a significant reduction in MDA, and a profound (p ≤ 0.05) elevation in the amount of photosynthetic pigments, GSH and AsA, along with the enhanced activities of antioxidative enzymes (SOD, POD, and CAT). In this way, Cu toxicity was alleviated. P fertilizers not only enhance the phytoremediation efficiency of Cu-contaminated soils by R. communis, but they also facilitate detoxification, which improves our understanding of the role of P in phytoremediation technologies.

Contributions of root cell wall polysaccharides to Cu sequestration in castor (Ricinus communis L.) exposed to different Cu stresses.

Cell wall polysaccharides play a vital role in binding with toxic metals such as copper (Cu) ions. However, it is still unclear whether the major binding site of Cu in the cell wall varies with different degrees of Cu stresses. Moreover, the contribution of each cell wall polysaccharide fraction to Cu sequestration with different degrees of Cu stresses also remains to be verified. The distribution of Cu in cell wall polysaccharide fractions of castor (Ricinus communis L.) root was investigated with various Cu concentrations in the hydroponic experiment. The results showed that the hemicellulose1 (HC1) fraction fixed 44.9%-67.8% of the total cell wall Cu under Cu stress. In addition, the pectin fraction and hemicelluloses2 (HC2) fraction also contributed to the Cu binding in root cell wall, accounting for 11.0%-25.9% and 14.1%-26.6% of the total cell wall Cu under Cu treatments, respectively. When the Cu levels were ≤25 µmol/L, pectin and HC2 contributed equally to Cu storage in root cell wall. However, when the Cu level was higher than 25 µmol/L, the ability of the pectin to bind Cu was easy to reach saturation. Much more Cu ions were bound on HC1 and HC2 fractions, and the HC2 played a much more important role in Cu binding than pectin. Combining fourier transform infrared (FT-IR) and two-dimensional correlation analysis (2D-COS) techniques, the hemicellulose components were showed not only to accumulate most of Cu in cell wall, but also respond fastest to Cu stress.

Differential responses of growth, photosynthesis, oxidative stress, metals accumulation and NRAMP genes in contrasting Ricinus communis genotypes under arsenic stress.

Effect of arsenate [As(V)] on biomass, photosynthetic rate, stomatal conductance, transpiration, oxidative stress, accumulation of As, Fe, Zn, Cu and Mn and expression of NRAMP genes was investigated in As(V) tolerant and sensitive genotypes of bioenergy crop Ricinus communis. As(V) treatments (100 and 200 µM) led to significant reduction in root and leaf biomass, photosynthetic rate, stomatal conductance and transpiration in GCH 2 and GCH 4 genotypes but no significant change or increase was observed in WM and DCH 177 genotypes. No significant difference was observed in hydrogen peroxide content and lipid peroxidation in As(V)-treated tolerant genotypes compared to control, whereas these parameters enhanced significantly in As(V)-treated sensitive genotypes. GCH 2 accumulated around two times As in leaves and showed significant reduction in concentration of Zn and Mn in the leaves and roots due to 200 µM As(V) treatment compared to WM. NRAMP genes are critical for uptake and distribution of essential divalent metal cations, photosynthesis and controlled production of reactive oxygen species in plants. RcNRAMP2, RcNRAMP3 and RcNRAMP5 genes showed differential expression in response to 200 µM As(V) in GCH 2 and WM suggesting that NRAMP genes are associated with differential responses of WM and GCH 2 genotypes to As(V) stress.

Synthesis and bioactivity of indoleacetic acid-carbendazim and its effects on Cylindrocladium parasiticum.

Indoleacetic acid (IAA)-carbendazim was synthesized to assess whether this conjugate could retain the fungicidal activity of carbendazim and gain root-inducing properties upon the addition of an indoleacetic acid group. An indoor virulence test demonstrated that the conjugate retained the fungicidal activity of carbendazim towards Cylindrocladium parasiticum. The conjugate was detected in roots after soaking Ricinus communis L. leaves into a solution of the IAA-carbendazim, which confirmed its phloem mobility. The activities of the cellulase, polygalacturonase and xylanase produced by Cylindrocladium parasiticum treated with different concentrations of the conjugate were determined, and the peak activities appeared at 72 h or 96 h. More importantly, the conjugate showed the ability to promote root growth. These results revealed that indoleacetic acid-carbendazim may be useful in preventing Cylindrocladium parasiticum and other diseases.

Characteristics of cadmium accumulation and isotope fractionation in higher plants.

Cadmium (Cd) pollution of the soil is an important global environmental issue owing to its great toxicity. The study of metal isotope fractionation is a novel technique that could be used to identify and quantify metal uptake and transport mechanisms in plant. In this study, cadmium tolerant Ricinus communis and hyperaccumulator Solanum nigrum have been cultured in different Cd concentration nutrient solutions. The Cd isotope values, metal elements concentrations in the organs (root, stem and leaf) in the two plant species have been measured during the growth periods (10d, 15d, 20d, 25d, and 30d). The results indicate that the organs of S. nigrum could be enriched with lighter Cd isotopes compared with R. communis. In addition, the Cd isotope fractionation become smaller when the plants were subjected to high Cd toxicity, which indicates that Cd isotope fractionation reflected the extent of Cd toxicity to plants. This study advances our current view of Cd translocation machination in plants.

Ozone risk assessment of castor (Ricinus communis L.) cultivars using open top chamber and ethylenediurea (EDU).

Castor bean (Ricinus communis L.) an important non-edible oilseed crop, is a prominent feed stock towards the generation of renewable materials for industrial production which has multiple applications ranging from cosmetics to biofuels industry. India accounts for 76% of the total world production of castor oil seed. However, major concern for developing countries like India where expanding economy led to rapid increases in gases like NOx, CO and VOCs photochemically form ozone. Ozone is strong oxidant that damages agriculture, ecosystems, and materials with considerable reduction in crop yields and crop quality. One way to reduce ozone induced loss is to focus on the adapting crops to ozone exposure by selecting cultivars with demonstrated ozone resistance. An experiment was conducted for ozone risk assessment of castor cultivars to select cultivar with demonstrated resistance against ozone pollution. This study comprise an open top chamber experiment with three treatments viz. (i) control (ambient ozone concentration), (ii) enhanced ozone (average 75 ppb for 4 h daily throughout the growing season), and (iii) EDU application. Results suggested that the ozone pollution substantially affected growth and physiology of castor cultivars. Crop biomass and yield was also negatively influenced by ozone pollution. Developed defence provided strength to withstand against ozone pollution to the experimental crop cultivars. However, developed defence is cultivar specific and positively correlated with the resistance against ozone pollution. Study concluded that the damage to ozone is directly dependent on the antioxidative potential of plant species. However, ozone adaptability is based on the genetic makeup of the cultivar and yield related loss to ozone can be minimizing by selecting ozone tolerant variety as seen in cultivar Nidhi-999.

Development of chitosan-PEG blended films using Trichoderma: Enhancement of antimicrobial activity and seed quality.

Fungi under genus Trichoderma as ameliorates of biotic and abiotic stresses in cultivated crops is gaining popularity world-wide and their application in conjunction with seed coating polymers is an attractive proposition to reduce bioagent wastage and harnessing benefits of combined application. The synergistic action of Trichoderma with natural polymers like chitosan can enhance antimicrobial activity. A series of blended film solutions were synthesized by using chitosan, PEG and plasticizer in varying concentrations. The optimization of blended film composition and dose for coating of seeds was done w.r.t seed coating. Studies on compatibility of film forming ingredients with Trichoderma have not shown any inhibition and antimicrobial activity has shown different levels of inhibition of plant pathogens. Films were structurally characterized by XRD, SEM, FT-IR, TGA, DSC. The optimized film solution in combination with different Trichoderma strains improved seed quality parameters in test crop castor (Ricinus communis). Significant increase in vigour index (3110) was observed with Th4d treatment followed by chitosan and Th4d combination formulation (3023). In conclusion, the optimized chitosan-PEG-Th blend was effective in enhancing seed germination and plant growth of castor. The material can be further tested under large field evaluation as a seed coating agent against various plant diseases.

Pb-induced phytotoxicity in para grass (Brachiaria mutica) and Castorbean (Ricinus communis L.): Antioxidant and ultrastructural studies.

Hydroponics experiment was conducted to investigate the effects of different levels of Pb on Para Grass (Brachiaria mutica) and Castorbean (Ricinus communis L). Generally, Para Grass exhibited higher tolerance to excessive concentrations of Pb in nutrient solution, whereas a consistent decline was observed in growth of Castorbean plants exposed to similar Pb levels. Malondialdehyde (MDA) and H2O2 contents exhibited contrasting results with a general decrease in Para Grass and a linear increase in case of Castorbean. In both species a decrease was noticed in the activities of superoxide dismutase (SOD) and guaiacol peroxidase (G-POD) while catalase (CAT) activity was significantly increased. Ultrastructural studies revealed increased starch grains and adversely affected thylakoid membranes in chloroplasts of leaf cells of plants treated with 500 µM Pb. Photosynthetic parameters such as CO2 assimilation rate, stomatal conductance (gs) and transpiration rate (E) decreased in both plant species under different levels of Pb. Maximum concentrations of Pb in shoots of Para Grass and Castorbean were 1.29 and 0.352 g kg-1, respectively while in roots maximum values were 8.88 and 49.86 g kg-1, respectively. The high concentrations of Pb (about 5%) in the roots of Castorbean plants suggest its possible role in the phytoremediation/rhizofiltration of Pb contaminated water.

Synthesis, fungicidal activity and phloem mobility of phenazine-1-carboxylic acid-alanine conjugates.

Phenazine-1-carboxylic acid (PCA) is a natural product that has been proven effective against a number of soil-borne fungal phytopathogens and registered for biofungicide against rice sheath blight in China. In order to improve the phloem mobility of phenazine-1-carboxylic acid (PCA), four PCA derivatives were designed and synthesized by conjugating PCA with l-alanine methyl ester, d-alanine methyl ester, l-alanine and d-alanine respectively. In vitro and planta bioassays results showed that conjugates L-PAM and D-PAM exhibited higher fungicidal activities against Rhizoctonia solani Kuhn than PCA while L-PA and D-PA were less active than PCA. The concentration of conjugates in Ricinus communis phloem sap was determined by HPLC. The results showed that only L-PA exhibited phloem mobility among these conjugates, and its concentration in Ricinus communis phloem sap increased with the increase of time (the maximum concentration was 12.69µM within 5h). However, the results of pot experiments showed that L-PA and other conjugates didn't exhibited the inhibition for the growth of Rhizoctonia solani Kuhn in the lower leaves after treatment in the upper leaves of rice seedlings. This may be due to the poor plant absorbility for them or their too little amount of accumulation in the lower leaves.

Effects of sulfur on toxicity and bioavailability of Cu for castor (Ricinus communis L.) in Cu-contaminated soil.

The biogeochemical cycling of sulfur (S) in soil has an important impact on the bioavailability of heavy metals and affects the utilization of soil polluted by heavy metals. In addition, S-containing compounds are involved in heavy metal detoxification. This study investigated the effects of S on the toxicity and bioavailability of copper (Cu) in castor (Ricinus communis L.) grown in Cu-contaminated mine tailings. The results showed that the application of S reduced the accumulation of Cu in castor and promoted its growth. With the addition of S, the malondialdehyde (MDA) content of castor leaves decreased significantly compared with control plants, indicating the alleviation of oxidative stress. Superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) content decreased significantly with the alleviation of oxidative stress. The sequential extraction of Cu fractions showed that the application of S significantly reduced the reducible Cu fraction, and increased the oxidizable Cu fraction. It also increased the residual Cu fraction in the soil. The transformation of chemical speciation reduced the bioavailability of Cu in soil, which then reduced the accumulation of Cu in castor. Our results demonstrated that S application was effective at promoting castor growth by reducing the bioavailability and uptake of Cu in Cu-contaminated mine tailings.

Effects of introducing theanine or glutamic acid core to tralopyril on systemicity and insecticidal activity.

Tralopyril was the active agent of a pro-insecticide chlorfenapyr. To simultaneously solve the problems of the phytotoxicity and non-systemic insecticidal activity of tralopyril, four new tralopyril conjugates containing theanine or glutamic acid moieties were designed and synthesized. Their phytotoxicity to tea shoot, phloem systemicity, and insecticidal activity were evaluated. Phytotoxic symptoms were not observed after the tea shoots were exposed to the four conjugates at concentrations of 2mM. The phloem mobility test on Ricinus communis L. seedlings confirmed that all four conjugates were mobile in the sieve tubes. Results of insecticidal activity against the third-instar larvae of Plutella xylostella showed that only conjugate 20 exhibited activity with an LC50 value of 0.5882±0.0504mM. After root application to tea seedlings, conjugate 20 showed obviously systemic insecticidal activity against Dendrothrips minowai Priesner, while chlorfenapyr showed no attribute of that. A new conjugate as potential phloem mobile pro-insecticide candidate was provided and so a novel strategy of pro-insecticide for improved phloem systemicity was proposed.

Comparison of chelates for enhancing Ricinus communis L. phytoremediation of Cd and Pb contaminated soil.

We studied chelate effects on castor bean (Ricinus communis L.) growth. These effects included Cd and Pb accumulation in plant tissues and the chemical behavior of Cd and Pb in the plant rhizosphere and non-rhizosphere. Tests were conducted in a glasshouse using the rhizobag method. Two castor bean cultivars (Zibo-3 and Zibo-9) were grown in soil contaminated with 3.53mg/kg Cd and 274mg/kg Pb. The soil was treated with citric acid (CA), ethylenediamine disuccinic acid (EDDS) or ethylenediamine tetraacetic acid (EDTA) (5mmol/kg). EDDS-treated soil produced 28.8% and 59.4% greater biomass for Zibo-3 and Zibo-9 respectively. In contrast, CA and EDTA inhibited the growth of the two cultivars. Zibo-9 had greater tolerance than Zibo-3 to chelate toxicity. Based on Cd and Pb plant uptake, EDDS could substitute for EDTA for phytoremediation of Cd in soil. EDTA was the most effective of the three chelates for Pb phytoremediation but it is less suitable for field use due to toxicology environmental persistence. Acid extractable Cd and Pb in the rhizosphere or reducible Cd and Pb in the non-rhizosphere of soil were the main influences on Cd and Pb accumulation in castor bean.

Molybdenum (Mo) increases endogenous phenolics, proline and photosynthetic pigments and the phytoremediation potential of the industrially important plant Ricinus communis L. for removal of cadmium from contaminated soil.

Cadmium (Cd) in agricultural soil negatively affects crops yield and compromises food safety. Remediation of polluted soil is necessary for the re-establishment of sustainable agriculture and to prevent hazards to human health and environmental pollution. Phytoremediation is a promising technology for decontamination of polluted soil. The present study investigated the effect of molybdenum (Mo) (0.5, 1.0 and 2.0 ppm) on endogenous production of total phenolics and free proline, plant biomass and photosynthetic pigments in Ricinus communis plants grown in Cd (25, 50 and 100 ppm) contaminated soils and the potential for Cd phytoextraction. Mo was applied via seed soaking, soil addition and foliar spray. Foliar sprays significantly increased plant biomass, Cd accumulation and bioconcentration. Phenolic concentrations showed significantly positive correlations with Cd accumulation in roots (R 2 = 0.793, 0.807 and 0.739) and leaves (R 2 = 0.707, 721 and 0.866). Similarly, proline was significantly positively correlated with Cd accumulation in roots (R 2 = 0.668, 0.694 and 0.673) and leaves (R 2 = 0.831, 0.964 and 0.930). Foliar application was found to be the most effective way to deliver Mo in terms of increase in plant growth, Cd accumulation and production of phenolics and proline.

Dissipation of excess photosynthetic energy contributes to salinity tolerance: a comparative study of salt-tolerant Ricinus communis and salt-sensitive Jatropha curcas.

The relationships between salt tolerance and photosynthetic mechanisms of excess energy dissipation were assessed using two species that exhibit contrasting responses to salinity, Ricinus communis (tolerant) and Jatropha curcas (sensitive). The salt tolerance of R. communis was indicated by unchanged electrolyte leakage (cellular integrity) and dry weight in leaves, whereas these parameters were greatly affected in J. curcas. The leaf Na+ content was similar in both species. Photosynthesis was intensely decreased in both species, but the reduction was more pronounced in J. curcas. In this species biochemical limitations in photosynthesis were more prominent, as indicated by increased C(i) values and decreased Rubisco activity. Salinity decreased both the V(cmax) (in vivo Rubisco activity) and J(max) (maximum electron transport rate) more significantly in J. curcas. The higher tolerance in R. communis was positively associated with higher photorespiratory activity, nitrate assimilation and higher cyclic electron flow. The high activity of these alternative electron sinks in R. communis was closely associated with a more efficient photoprotection mechanism. In conclusion, salt tolerance in R. communis, compared with J. curcas, is related to higher electron partitioning from the photosynthetic electron transport chain to alternative sinks.

Rings B,D-seco limonoid antifeedants from Swietenia mahogani.

Three phragmalin-type limonoids, swietephragmin H (1), swietephragmin I (2) and 11-hydroxyswietephragmin B (3), and a mexicanolide-type limonoid 2-hydroxy-6-deacetoxyswietenine (4), together with known compounds, 6-O-acetyl-2-hydroxyswietenin (5), 2-hydroxyswietenine (6), swietemahonin G (7), methyl 6-hydroxyangolensate (8) and 7-deacetoxy-7-oxogedunin (9) were isolated from the leaves of Swietenia mahogani (Meliaceae). Their structures were established by extensive NMR experiments in conjunction with mass spectrometry. The antifeedant activity of the isolated compounds was evaluated.

Cadmium tolerance and its phytoremediation by two oil yielding plants Ricinus communis (L.) and Brassica juncea (L.) from the contaminated soil.

The effect of increasing level of cadmium in soil was investigated on biomass production, antioxidants, Cd bioaccumulation and translocation in Ricinus communis vis-à-vis a commonly studied oil crop Brassica juncea. The plants were exposed to 25, 50, 75, 100, and 150 mg Cd/Kg soil for up to 60 days. It was found that R. communis produced higher biomass at all the contamination levels than that of B. juncea. Proline and malondialdehyde in the leaves increased with increase in Cd level in both the species, whereas soluble protein decreased. The bioaccumulation of Cd was higher in B. juncea on the basis of the per unit biomass, total metal accumulation per plant was higher in R. communis. The translocation of Cdfrom roots to shoot was also higher in B. juncea at all Cd concentrations. R. communis appeared more tolerant and capable to clean Cd contaminated soil for longer period in one sowing than B. juncea and the former can grow in wasteland soil also in which later cannot be cultivated.

Phytoaccumulation and tolerance of Riccinus communis L. to nickel.

The phytotoxicity due to nickel (Ni) and its accumulation in castor (Ricinus communis L.) plant of Euphorbiaceae family resulting from its addition from low to very high levels to a swell-shrink clayey soil (Haplustert) was studied in a pot culture experiment. Nine levels of Ni (0, 10, 40, 80, 120, 160, 180, 200, 250 mg Ni kg(-1) soil) were applied. Crop was harvested at 45 days after sowing. At the higher Ni levels, beyond 200 mg Ni kg(-1) soil, reduced growth symptom was recorded. The concentration of Ni in plant parts increased with increasing dose of applied Ni. Nickel concentration in castor root ranged from traces (control) to 455 mg kg(-1) and was directly related to soil Ni concentration. At 200 mg Ni kg(-1) soil, dry matter yield of castor reduced to 10% of control plant. Significant changes were observed in the roots of castor treated with higher levels of Ni against control. The roots treated with Ni showed a decrease in number of cells in the cortex region. It also appeared that the cortex region consisted of elongated parenchymatous cells instead of the normal parenchymatous tissue as in the control plant. Regarding Ni accumulation capacity, castor plant was recorded as an accumulator (alpha = 0.11 and beta = 1.10). A laboratory study was also conducted in the experimental soil to know the different operationally defined fractions of Ni, which control the availability of Ni to castor. Different fractions of Ni present in this soil followed this order: Residual > Fe-Mn oxides > carbonate > organic > exchangeable > water soluble. Overall results depict that castor is a promising species which can be used as a potential plant for phytoremediation of contaminated soils and to improve soil quality and provide economical benefits.

Inoculation of Ni-resistant plant growth promoting bacterium Psychrobacter sp. strain SRS8 for the improvement of nickel phytoextraction by energy crops.

This study was conducted to elucidate effects of inoculating plant growth-promoting bacterium Psychrobacter sp. SRS8 on the growth and phytoextraction potential of energy crops Ricinus communis and Helianthus annuus in artificially Ni contaminated soils. The toxicity symptom in plants under Ni stress expressed as chlorophyll, protein content, growth inhibition, and Fe, P concentrations were studied, and the possible relationship among them were also discussed. The PGPB SRS8 was found capable of stimulating plant growth and Ni accumulation in both plant species. Further, the stimulation effect on plant biomass, chlorophyll, and protein content was concomitant with increased Fe and P assimilation from soil to plants. Further, the induction of catalase and peroxidase activities was also involved in the ability of SRS8 to increase the tolerance in both plant species under Ni stress. The findings suggest that strain SRS8 play an important role in promoting the growth and phytoextraction efficiency of R. communis and H. annuus, which may be used for remediation of metal contaminated sites.

Salicylic acid transport in Ricinus communis involves a pH-dependent carrier system in addition to diffusion.

Despite its important functions in plant physiology and defense, the membrane transport mechanism of salicylic acid (SA) is poorly documented due to the general assumption that SA is taken up by plant cells via the ion trap mechanism. Using Ricinus communis seedlings and modeling tools (ACD LogD and Vega ZZ softwares), we show that phloem accumulation of SA and hydroxylated analogs is completely uncorrelated with the physicochemical parameters suitable for diffusion (number of hydrogen bond donors, polar surface area, and, especially, LogD values at apoplastic pHs and Delta LogD between apoplast and phloem sap pH values). These and other data (such as accumulation in phloem sap of the poorly permeant dissociated form of monohalogen derivatives from apoplast and inhibition of SA transport by the thiol reagent p-chloromercuribenzenesulfonic acid [pCMBS]) lead to the following conclusions. As in intestinal cells, SA transport in Ricinus involves a pH-dependent carrier system sensitive to pCMBS; this carrier can translocate monohalogen analogs in the anionic form; the efficiency of phloem transport of hydroxylated benzoic acid derivatives is tightly dependent on the position of the hydroxyl group on the aromatic ring (SA corresponds to the optimal position) but moderately affected by halogen addition in position 5, which is known to increase plant defense. Furthermore, combining time-course experiments and pCMBS used as a tool, we give information about the localization of the SA carrier. SA uptake by epidermal cells (i.e. the step preceding the symplastic transport to veins) insensitive to pCMBS occurs via the ion-trap mechanism, whereas apoplastic vein loading involves a carrier-mediated mechanism (which is targeted by pCMBS) in addition to diffusion.

Effect of some heavy metals and soil humic substances on the phytochelatin production in wild plants from silver mine areas of Guanajuato, Mexico.

Phytochelatins (PCs) were determined in the wild plants, focusing on their relationship with the levels of heavy metals and humic substances (HS) in soil. Ricinus communis and Tithonia diversifolia were collected from several sites in Guanajuato city (Mexico), which had long been the silver and gold mining center. The analysis of PCs in root extracts was carried out by liquid chromatography (derivatization with monobromobimane). Total Ag, Cd, Cu and Pb in plant roots and in soil samples, as well as soil HS were determined. The association of metals with HS in soils was evaluated by size exclusion chromatography (SEC) with UV and ICP-MS detection. The results obtained revealed the induction of PCs in R. communis but not in T. diversifolia. The levels of Cd and Pb in plant roots presented strong positive correlation with PC-2 (r=0.9395, p=0.005; r=0.9573, p=0.003, respectively), indicating that these two metals promote PCs induction in R. communis. On the other hand, the inverse correlation was found between soil HS and metal levels in roots of R. communis (Cu>Pb>Cd>Ag), in agreement with the decreasing affinity of these metals to HS. Importantly, the inverse correlation between soil HS and plant PC-2 was observed (r=-0.7825, p=0.066). These results suggest that metals strongly bound to HS could be less bioavailable to plants, which in turn would limit their role in the induction of PCs. Indeed, the SEC elution profiles showed Pb but not Cd association with HS and the correlation between metal in soil and PC-2 in plant was statistically significant only for Cd (r=0.7857, p=0.064). Based on these results it is proposed that the role of heavy metals in PCs induction would depend on their uptake by R. communis, which apparently is controlled by the association of metals with soil HS. This work provides further evidence on the role of environmental conditions in the accumulation of heavy metals and phytochelatin production in plants.