Enhanced photochemical efficiency of PSII in Prosopis juliflora suggests contribution to invasion advantage over native C3 xero-halophytes under salt stress.

Chlorophyll a fluorescence parameters related to PSII photochemistry, photoprotection and photoinhibition were investigated in four C3 plant species growing in their natural habitat: Prosopis juliflora ; Abutilon indicum ; Salvadora persica ; and Phragmites karka . This study compared the light reaction responses of P. juliflora , an invasive species, with three native co-existing species, which adapt to varying water deficit and high salt stress. Chlorophyll a fluorescence quenching analyses revealed that P. juliflora had the highest photochemical quantum efficiency and yield, regulated by higher fraction of open reaction centres and reduced photoprotective energy dissipation without compromising the integrity of photosynthetic apparatus due to photoinhibition. Moreover, the elevated values of parameters obtained through polyphasic chlorophyll a fluorescence induction kinetics, which characterise the photochemistry of PSII and electron transport, highlighted the superior performance index of energy conservation in the transition from excitation to the reduction of intersystem electron carriers for P. juliflora compared to other species. Enhanced pigment contents and their stoichiometry in P. juliflora apparently contributed to upregulating fluxes and yields of energy absorbance, trapping and transport. This enhanced photochemistry, along with reduced non-photochemical processes, could explain the proclivity for invasion advantage in P. juliflora across diverse stress conditions.

Differential effects of NaCl and Na2SO4 on the halophyte Prosopis strombulifera are explained by different responses of photosynthesis and metabolism.

Prosopis strombulifera (Lam.) Benth. is a halophytic shrub found in highly saline soils in Argentina, with high tolerance against NaCl but strong growth inhibition by Na2SO4. In the present study, the differences in the physiological responses caused by these salts and an iso-osmotic combination thereof on photosynthesis, mineral composition and metabolism were analyzed. Na2SO4 treated plants were the most affected by salinity, showing a significant decrease in several photosynthetic parameters. Proline and cysteine accumulated significantly in the plants in response to salt stress. These results show by the first time that the SO42- anion is triggering damage in the photosynthetic apparatus and consequently affecting the photosynthetic process, which may explain the strong growth inhibition in these plants at high salinity. Moreover, the SO42- anion provoke challenges in the incorporation of nutrients, decreasing the levels of K, Ca, P and Mg, and inducing a strong antioxidant activity in P. strombulifera.

Improvement in fluoride remediation technology using GIS based mapping of fluoride contaminated groundwater and microbe assisted phytoremediation.

Fluoride (F) in groundwater is a major issue of water pollution. Geo-statistical analysis of groundwater quality in Newai Tehsil, (India) has been done in order to identify the possible spatial distribution of water quality parameters and to assess the spatial dependence of water properties with the help of principal component analysis (PCA) structure. Two types of maps (spatial map and principal component map) of groundwater quality have been developed. A field experiment was conducted to investigate the effect of different Fluoride (F) concentration combined with Pseudomonas fluorescens (P.F) on Prosopis juliflora plant. The field design was used as completely randomized block design with three replicates. Study revealed that parameters were found to be positively and highly correlated with principal component. Low and high values (with their acceptable limit) have also been displayed over the each spatial map. Plants treated with P. fluorescens showed the highest F uptake in root, shoot and leaves tissues were 33.14, 19.41 and 15.15 mg kg-1 after 120 days, respectively. Both total bioaccumulation factor (BF) and translocation factor (TF) were obtained above one i.e., 1.06 and 1.04, this confirmed the high accumulation and translocation of F in plant tissues. The F uptake efficiency of plant was enhanced to 67.7% and plant biomass was increased upto 57.03%. According to the available literature, this is the first spatial field study for the remediation of F polluted soil through P. fluorescens. The present study will be beneficial for researchers working towards further improvement of F phytoremediation technology. Also, GIS based study can be very useful for decision maker's exploration of groundwater to understand the potential of present research work on fluoride contamination.

Effect of Fe3O4 NPs application on fluoride (F) accumulation efficiency of Prosopis juliflora.

Fluoride (F) pollution is a major worldwide problem affecting approximately 200 million people. Hyperaccumulator plant Prosopis juliflora has been used for the removal of F from contaminated soils; however it's low F accumulation efficiency and low biomass limits the phytoremediation efficiency. Present study deals with enhancement of F uptake efficiency of plant P. juliflora through iron oxide nanoparticles (Fe3O4 NPs) application for remediation of agricultural soils. For the study, Fe3O4 NPs were synthesized through green route using waste jojoba leaves. The application of Fe3O4 NPs significantly increased the shoot and root length of plant P. juliflora. Fe3O4 NPs treatment also promoted the F accumulation in shoot and root tissues upto 28.43 and 34.64 mg kg-1, respectively. Microscopic (FESEM and light microscopic) and EDX spectrum analysis of plant tissues confirmed the accumulation and translocation of Fe3O4 NPs and F in plant tissues This nano-phytoremediation approach could be a better option for F remediation for agricultural and commercial purpose.

Changes in the phenylalanine ammonia lyase activity, total phenolic compounds, and flavonoids in Prosopis glandulosa treated with cadmium and copper.

The aim of the present work is to evaluate the changes on the phenylalanine ammonia lyase (PAL) activity, phenolic compounds accumulation and photochemical efficiency in leaves of P. glandulosa treated with Cd2+ (0.001 M) and Cu2+ (0.52 M) concentrations for 96 h under hydroponic conditions. The results showed that only leaves treated with copper had a decrease in photochemical efficiency and leaf epidermal polyphenols in P. glandulosa leaves after 96 h of exposure. On the other hand the reverse-phase HPLC analysis revealed higher levels of phenolic compound (gallic, vanillic and caffeic acids) and flavonoids (rutin and kaempferol-3-O-glucosides) in plant leaves from Cu and Cd-treatments with respect to control plants. Finally, highest increments in PAL activity was observed in extracts of leaves treated with Cu and Cd (about 205 and 284%), respectively, with respect to control plants after 96 h treatment. These suggest that activation of phenylpropanoid pathway represent a source of nonenzymatic antioxidants that protect at P. glandulosa against oxidative stress when exposed to cadmium and copper. Hence future studies are necessary to elucidate the participation of phenylpropanoid pathway in the reduction of metal toxicity in Prosopis species.

Favouring NO over H2O2 production will increase Pb tolerance in Prosopis farcta via altered primary metabolism.

Reactive oxygen species (ROS) and nitric oxide (NO) are known in triggering defense functions to detoxify heavy metal stresses. To investigate the relevance of ROS production, Pb treatment (400µM) alone and in combination with 400µM sodium ascorbate (Asc: as H2O2 scavenger) were given to hydroponically grown Prosopis farcta seedlings over a time course of 72h. Data presented here indicate that, the low extent of H2O2 due to scavenging by ascorbate, together with high level of NO improved Pb+Asc- treated Prosopis growth. Following the evoked potential of both the signals, significant increases in phenolic acids; caffeic, ferulic and salicylic acid were observed with Pb treatment; which are consistent with observed increase in lignin content and consequently with growth inhibition. In contrast, Pb+Asc treatment induced more flavonoids (quercetin, kaempferol, luteolin), diminished phenolic acids contents and also lignin. Elicited expression rate of phenylalanine ammonia-lyase gene (PAL) and also its enzymatic activity verified the induced phenylpropanoid metabolism by Pb and Pb+Asc treatments. In comparison with Pb stress, Asc+Pb application induced the high expression of arginine decarboxylase gene (ADC), in polyamines biosynthesis pathway, and conducted the N flow towards polyamines and γ-amino butyric acid (GABA). Examining the impact on enzyme activities, catalase, and guaiacol peroxidase; Pb+Asc reduced activity but this increased ascorbate peroxidase, and aconitase activity. Our observations are consistent with conditions favouring NO production and reduced H2O2 can improve Pb tolerance via wide-ranging effects on a primary metabolic network.

Expression of metallothionein type 2 and 3 genes in Prosopis glandulosa leaves treated with copper.

For a better understanding of the strategies that are used by Prosopis glandulosa in heavy metal tolerance, the present study evaluated the gene expression of three metallothioneins (MTs; PgMt2-1, PgMt2, and PgMt3) in plants exposed to sub-lethal concentrations of copper. The PgMt2-1, PgMt2, and PgMt3 sequences were homologous to the MT type 2 (isoform 1), Mt2, and Mt3 sequences of other plant species found in GenBank. A reverse transcriptase-polymerase chain reaction showed that treatment with 100 mM Cu2+ induced a significant increase in PgMt2 and PgMt3 expression during the first 4 h of exposure compared to that of PgMt2-1. However, after 8 h of exposure, the expression levels of PgMt2 and PgMt3 were significantly lower than those of PgMt2-1. PgMt transcript levels only increased significantly during the first hour after exposure to copper, suggesting that PgMts could play a key role in the plant's detoxification mechanism. However, additional studies are required to confirm MTs as a mechanism of heavy metal tolerance and accumulation in this species.

A novel heavy metal ATPase peptide from Prosopis juliflora is involved in metal uptake in yeast and tobacco.

Heavy metal pollution of agricultural soils is one of the most severe ecological problems in the world. Prosopis juliflora, a phreatophytic tree species, grows well in heavy metal laden industrial sites and is known to accumulate heavy metals. Heavy Metal ATPases (HMAs) are ATP driven heavy metal pumps that translocate heavy metals across biological membranes thus helping the plant in heavy metal tolerance and phytoremediation. In the present study we have isolated and characterized a novel 28.9 kDa heavy metal ATPase peptide (PjHMT) from P. juliflora which shows high similarity to the C-terminal region of P1B ATPase HMA1. It also shows the absence of the invariant signature sequence DKTGT, and the metal binding CPX motif but the presence of conserved regions like MVGEGINDAPAL (ATP binding consensus sequence), HEGGTLLVCLNS (metal binding domain) and MLTGD, GEGIND and HEGG motifs which play important roles in metal transport or ATP binding. PjHMT, was found to be upregulated under cadmium and zinc stress. Heterologous expression of PjHMT in yeast showed a higher accumulation and tolerance of heavy metals in yeast. Further, transgenic tobacco plants constitutively expressing PjHMT also showed increased accumulation and tolerance to cadmium. Thus, this study suggests that the transport peptide from P. juliflora may have an important role in Cd uptake and thus in phytoremediation.

Metabolomic profiling of the halophyte Prosopis strombulifera shows sodium salt- specific response.

Primary and secondary metabolite profiles were analyzed in roots and leaves of the halophytic shrub Prosopis strombulifera in response to control plants (no salt added in the growing media) and to lowering the osmotic potential to -1.0, -1.9, and -2.6 MPa generated by NaCl, Na2SO4, and the iso-osmotic combination of them at 24 h after reaching such potential. A rapid production of metabolites in response to sodium salt was found, which was correlated with modifications in growth parameters. Analysis of polar metabolite profiles by GC-MS rendered a total of 108 significantly altered compounds including 18 amino acids, 19 secondary metabolites, 23 carbohydrates, 13 organic acids, 4 indole acids, among others. Primary metabolites showed a differential response under the salt treatments, which was dependent on salt type and concentration, organ and age of plants. Most of identified compounds showed the strongest accumulation at the highest salt concentration assayed for Na2SO4-treated plants, which was correlated with damaging effects of sulfate anion on plant growth. Roots of NaCl-treated plants showed a higher number of altered metabolites (analyzed by UPLC-ESI-QqTOF-MS) compared to other treatments, while leaves of Na2SO4-treated plants showed the highest number of altered signals. A low degree of overlapping between secondary metabolites altered in roots and leaves of NaCl and Na2SO4-treated plants was found. However, when both NaCl and Na2SO4 salts were present plants always showed a lower number of altered metabolites. Three compounds were tentatively identified: tryptophan, lysophosphatidylcoline and 13-hydroxyoctadecadienoic acid. Increasing knowledge on P. strombulifera metabolism will contribute to unravel the underlying biochemical mechanism of salt tolerance.

Selection of suitable mineral acid and its concentration for biphasic dilute acid hydrolysis of the sodium dithionite delignified Prosopis juliflora to hydrolyze maximum holocellulose.

Two grams of delignified substrate at 10% (w/v) level was subjected to biphasic dilute acid hydrolysis using phosphoric acid, hydrochloric acid and sulfuric acid separately at 110 °C for 10 min in phase-I and 121 °C for 15 min in phase-II. Combinations of acid concentrations in two phases were varied for maximum holocellulose hydrolysis with release of fewer inhibitors, to select the suitable acid and its concentration. Among three acids, sulfuric acid in combination of 1 & 2% (v/v) hydrolyzed maximum holocellulose of 25.44±0.44% releasing 0.51±0.02 g/L of phenolics and 0.12±0.002 g/L of furans, respectively. Further, hydrolysis of delignified substrate using selected acid by varying reaction time and temperature hydrolyzed 55.58±1.78% of holocellulose releasing 2.11±0.07 g/L and 1.37±0.03 g/L of phenolics and furans, respectively at conditions of 110 °C for 45 min in phase-I & 121 °C for 60 min in phase-II.

Modulation of Pb-induced stress in Prosopis shoots through an interconnected network of signaling molecules, phenolic compounds and amino acids.

Lead (Pb) is a hazardous heavy metal present in the environment which elicits oxidative stress in plants. To characterize the physiological and biochemical basis of Pb tolerance, Prosopis farcta seedlings were exposed to Hoagland's solutions at six different Pb concentrations (0, 80, 160, 320, 400 and 480 µM) for different periods of time. As expected, application of Pb significantly increased hydrogen peroxide (H2O2) content. In response, P. farcta deployed the antioxidative defence mechanisms with significantly higher activities of superoxide dismutase (SOD), enzymes related to H2O2 removal, and also the increases in proline as a solute marker of stress. Increases were observed in nitric oxide (NO) production which could also act in triggering defense functions to detoxify Pb. Enhanced phenylalanine ammonia-lyase (PAL) activity at early days of exposure to Pb was correlated with increases in phenolic compounds. Significant increases in phenolic acids and flavonoids; daidzein, vitexin, ferulic acid and salicylic acid were observed with Pb treatment. Furthermore, the stress effects were followed by changes in free amino acid content and composition. Aspartic acid and glycine content was increased but glutamic acid significantly decreased. It is likely that stress signal transduction by NO and H2O2 mediated defence responses to Pb by coordination of antioxidative system and metabolic pathways of phenylpropanoid and amino acids.

Effects of copper sulfate on seedlings of Prosopis pubescens (screwbean mesquite).

Phytoextraction is an established method of removal of heavy metals from contaminated soils worldwide. Phytoextraction is most efficient if local plants are used in the contaminated site. We propose that Prosopis pubescens (Screw bean mesquite) would be a successful phytoextractor of copper in our local soils. In order to determine the feasibility of using Screw bean mesquite, we utilized inductively-coupled plasma-optical emission spectroscopy (ICP-OES) and elemental analysis to observe the uptake of copper and the effects on macro and micro nutrients within laboratory-grown seedlings. We have previously shown that P. pubescens is a hyperaccumulator of copper in soil-grown seedlings. Light and transmission electron microscopy demonstrated death of root cells and ultrastructural changes due to the presence of copper from 50 mg/L - 600 mg/L. Ultrastructural changes included plasmolysis, starch accumulation, increased vacuolation and swollen chloroplasts with disarranged thylakoid membranes in cotyledons. Inductively coupled plasma-optical emission spectroscopy analyses of macro- and micro-nutrients revealed that the presence of copper sulfate in the growth medium of Petri-dish grown Prosopis pubescens seedlings resulted in dramatic decreases of magnesium, potassium and phosphorus. At 500-600 mg/L of copper sulfate, a substantial increase of sulfur was present in roots.

Selection of the best chemical pretreatment for lignocellulosic substrate Prosopis juliflora.

Pretreatment is a pre-requisite step in bioethanol production from lignocellulosic biomass required to remove lignin and increase the porosity of the substrate for saccharification. In the present study, chemical pretreatment of Prosopis juliflora was performed using alkali (NaOH, KOH, and NH3), reducing agents (Na2S2O4, Na2SO3) and NaClO2 in different concentration ranges at room temperature (30±2 °C) to remove maximum lignin with minimum sugar loss. Further, biphasic acid hydrolysis of the various pretreated substrates was performed at mild temperatures. Considering the amount of holocellulose hydrolyzed and inhibitors released during hydrolysis, best chemical pretreatment was selected. Among all the chemicals investigated, pretreatment with sodium dithionite at concentration of 2% (w/v) removed maximum lignin (80.46±1.35%) with a minimum sugar loss (2.56±0.021%). Subsequent biphasic acid hydrolysis of the sodium dithionite pretreated substrate hydrolyzed 40.09±1.22% of holocellulose and released minimum amount of phenolics (1.04±0.022 g/L) and furans (0.41±0.012 g/L) in the hydrolysate.

Effects of fluoride on germination, early growth and antioxidant enzyme activities of legume plant species Prosopis juliflora.

Prosopis juliflora (Mimosoideae) is a fast growing and drought resistant tree of semi-arid region of India where fluoride (F) toxicity is a common problem. In the present investigations this species was fluoride tested to check their capacity as bioindicator plant and its efficiency to accumulate. To achieve this aim, P. juliflora seedlings grown in hydroponic culture containing different concentrations of F were analyzed for germination percentage together with some biochemical parameters viz, antioxidant enzyme activities, total chlorophyll and accumulation of F in different plant parts. After 15 days of treatment, root growth (r = -0.928, p < 0.01), shoot growth (r = -0.976, p < 0.01), vigor index (r = -0.984, p < 0.01) were in decreasing trend with increasing concentration of NaF. Both catalase (3.2 folds) and peroxidase (2.7 folds) enzymes activity increased with increase in F concentration. Plant accumulated larger portion of the F in the roots (1024.63 microg g(-1) d.wt.) followed by shoot (492.30 microg g(-1) d.wt.). As P. juliflora did not show any morphological changes (marginal and tip chlorosis of leaf portions, necrosis and together these features are referred to as leaf "tip-burn") therefore, this species may be used as suitable bioindicator species for potentially F affected areas. Further, higher accumulation of F in roots indicates that P. juliflora is a suitable species for the removal of F in phytoremediation purposes.

Different sodium salts cause different solute accumulation in the halophyte Prosopis strombulifera.

The success of Prosopis strombulifera in growing under high NaCl concentrations involves a carefully controlled balance among different processes, including compartmentation of Cl(-) and Na(+) in leaf vacuoles, exclusion of Na(+) in roots, osmotic adjustment and low transpiration. In contrast, Na(2) SO(4) causes growth inhibition and toxicity. We propose that protection of the cytoplasm can be achieved through production of high endogenous levels of specific compatible solutes. To test our hypothesis, we examined endogenous levels of compatible solutes in roots and leaves of 29-, 40- and 48-day-old P. strombulifera plants grown in media containing various concentrations of NaCl, Na(2) SO(4) or in mixtures of both, with osmotic potentials of -1.0,-1.9 and -2.6 MPa, as correlated with changes in hydric parameters. At 24 h after the last pulse plants grown in high NaCl concentrations had higher relative water content and relatively higher osmotic potential than plants grown in Na(2) SO(4) (at 49 days). These plants also had increased synthesis of proline, pinitol and mannitol in the cytoplasm, accompanied by normal carbon metabolism. When the sulphate anion is present in the medium, the capacities for ion compartmentalisation and osmotic adjustment are reduced, resulting in water imbalance and symptoms of toxicity due to altered carbon metabolism, e.g. synthesis of sorbitol instead of mannitol, reduced sucrose production and protein content. This inhibition was partially mitigated when both anions were present together in the solution, demonstrating a detrimental effect of the sulphate ion on plant growth.

Organ-wise accumulation of fluoride in Prosopis juliflora and its potential for phytoremediation of fluoride contaminated soil.

Fluoride (F) contamination is a global environmental problem, as there is no cure of fluorosis available yet. Prosopis juliflora is a leguminous perennial, phreatophyte tree, widely distributed in arid and semi-arid regions of world. It extensively grows in F endemic areas of Rajasthan (India) and has been known as a "green" solution to decontaminate cadmium, chromium and copper contaminated soils. This study aims to check the tolerance potential of P. juliflora to accumulate fluoride. For this work, P. juliflora seedlings were grown for 75 d on soilrite under five different concentrations of F viz., control, 25, 50, 75 and 100 mg NaF kg(-1). Organ-wise accumulation of F, bioaccumulation factor (BF), translocation factor (TF), growth ratio (GR) and F tolerance index (TI) were examined. Plant accumulated high amounts of F in roots. The organ-wise distribution showed an accumulation 4.41 mg kg(-1)dw, 12.97 mg kg(-1)dw and 16.75 mg kg(-1)dw F, in stem, leaves and roots respectively. The results indicated significant translocation of F from root into aerial parts. The bioaccumulation and translocation factor values (>1.0) showed high accumulation efficiency and tolerance of P. juliflora to F. It is concluded that P. juliflora is a suitable candidate for phytoremediation purpose and can be explored further for the decontamination of F polluted soils.

Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings.

Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p<0.05) and effective AMF colonization compared to controls grown in uninoculated compost-amended tailings. Mesquite shoot tissue lead and zinc concentrations did not exceed domestic animal toxicity limits regardless of whether AMF inoculation was used. The rhizosphere microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) profiles of the small subunit RNA gene for bacteria and fungi. Canonical correspondence analysis (CCA) of DGGE profiles showed that the rhizosphere fungal community structure at the end of the experiment was significantly different from the community structure in the tailings, compost, and AMF inocula prior to planting. Further, CCA showed that AMF inoculation significantly influenced the development of both the fungal and bacterial rhizosphere community structures after two months. The changes observed in the rhizosphere microbial community structure may be either a direct effect of the AMF inocula, caused by changes in plant physiology induced by AMF, or a combination of both mechanisms.

Over-expression of a Rab family GTPase from phreatophyte Prosopis juliflora confers tolerance to salt stress on transgenic tobacco.

Plant growth and productivity are adversely affected by various abiotic and biotic stress factors. In our previous study, we used Prosopis juliflora, an abiotic stress tolerant tree species of Fabaceae, as a model plant system for isolating genes functioning in abiotic stress tolerance. Here we report the isolation and characterization of a Rab family GTPase from P. juliflora (Pj Rab7) and the ability of this gene to confer salt stress tolerance in transgenic tobacco. Northern analysis for Pj Rab7 in P. juliflora leaf tissue revealed up-regulation of this gene under salt stress under the concentrations and time points analyzed. Pj Rab7 transgenic tobacco lines survived better under conditions of 150 mM NaCl stress compared to control un-transformed plants. Pj Rab7 transgenic plants were found to accumulate more sodium than control plants during salt stress. The results of our studies could be used as a starting point for generation of crop plants tolerant to abiotic stress.

Toxicity and biotransformation of uncoated and coated nickel hydroxide nanoparticles on mesquite plants.

Nanomaterials are of particular interest in environmental chemistry due to their unknown toxicity to living organisms. Reports indicate that nanoparticles (NPs) affect seed germination, but the uptake and biotransformation of metal nanoparticles is not well understood. The present study investigated the toxicity and biotransformation of Ni(OH)2 NPs by mesquite plants (Prosopis sp.). Three sets of plants were treated for four weeks with 0.01, 0.05, or 0.10 g of either uncoated or sodium citrate coated NPs before and after synthesis. Nickel concentrations in plants were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and the form and oxidation state of Ni was determined using X-ray absorption spectroscopy (XAS). Results showed that uncoated NPs had an average size of 8.7 nm, whereas coated NPs before and after synthesis had an average of 2.5 and 0.9 nm, respectively. The ICP-OES results showed that plants treated with 0.10 g of uncoated and coated NPs before and after synthesis had 803, 764, and 400 mg Ni kg dry weight, in the leaves, respectively. The XAS analyses showed Ni NPs in roots and shoots of plants treated with uncoated NPs, whereas leaves showed a Ni(II)-organic acid type complex. However, plants treated with coated NPs before or after synthesis showed Ni NPs only in roots and a Ni(II)-organic acid complex in shoots and leaves. Results also showed that none of the treatments reduced plant size or chlorophyll production. To the authors' knowledge, this is the first time that the biotransformation of nanoparticles by a plant system is reported.

A chloroplast-localized and auxin-induced glutathione S-transferase from phreatophyte Prosopis juliflora confer drought tolerance on tobacco.

Plant growth and productivity are adversely affected by various abiotic stress factors. In our previous study, we used Prosopis juliflora, a drought-tolerant tree species of Fabaceae, as a model plant system for mining genes functioning in abiotic stress tolerance. Large-scale random EST sequencing from a cDNA library obtained from drought-stressed leaves of 2-month-old P. juliflora plants resulted in identification of three different auxin-inducible glutathione S-transferases. In this paper, we report the cellular localization and the ability to confer drought tolerance in transgenic tobacco of one of these GSTs (PjGSTU1). PjGSTU1 was overexpressed in Escherichia coli and GST and GPX activities in total protein samples were assayed and compared with controls. The results indicated that PjGSTU1 protein forms a functional homo-dimer in recombinant bacteria with glutathione transferase as well as glutathione peroxidase activities. PjGSTU1 transgenic tobacco lines survived better under conditions of 15% PEG stress compared with control un-transformed plants. In vivo localization studies for PjGSTU1 using GFP fusion revealed protein localization in chloroplasts of transgenic plants. The peroxidase activity of PjGSTU1 and its localization in the chloroplast indicates a possible role for PjGSTU1 in ROS removal.