Application of zinc oxide nanoparticles as fertilizer boosts growth in rice plant and alleviates chromium stress by regulating genes involved in oxidative stress.

Chromium toxicity impairs the productivity of rice crops and raises a major concern worldwide and thus, it calls for unconventional and sustainable means of crop production. In this study, we identified the implication of zinc oxide nanoparticles (ZnO NPs) in promoting plant growth and ameliorating chromium-induced stress in seedlings of rice (Oryza sativa). This investigation demonstrates that the exogenous supplementation of ZnO NPs at 25 µM activates defense mechanisms conferring rice seedlings significant tolerance against stress imposed by the exposure of 100 µM Cr(VI). Further, supplementation of this nanofertilizer reversed the inhibitory effects of Cr(VI) on growth and photosynthetic efficiency. The growth promotion was primarily associated with the function of ZnO NPs in inducing activity of antioxidative enzymes i.e. APX, DHAR, MDHAR and GR belonging to the ascorbate-glutathione cycle in the Cr-exposed seedlings, exceeding the levels in control. The overexpression of these antioxidative genes correlated concomitantly with the decrease of oxidants including SOR and H2O2 and the increase in the levels of non-enzymatic antioxidants: AsA and GSH.

Nanotitania Exposure Causes Alterations in Physiological, Nutritional and Stress Responses in Tomato (Solanum lycopersicum).

Titanium dioxide nanoparticles (nanotitania: TiO2NPs) are used in a wide range of consumer products, paints, sunscreens, and cosmetics. The increased applications lead to the subsequent release of nanomaterials in environment that could affect the plant productivity. However, few studies have been performed to determine the overall effects of TiO2NPs on edible crops. We treated tomato plants with 0.5, 1, 2, and 4 g/L TiO2NPs in a hydroponic system for 2 weeks and examined physiological, biochemical, and molecular changes. The dual response was observed on growth and photosynthetic ability of plants depending on TiO2NPs concentrations. Low concentrations (0.5-2 g/L) of TiO2NPs boosted growth by approximately 50% and caused significant increase in photosynthetic parameters such as quantum yield, performance index, and total chlorophyll content as well as induced expression of PSI gene with respect to untreated plants. The high concentration (4 g/L) affected these parameters in negative manner. The catalase and peroxidase activities were also elevated in the exposed plants in a dose-dependent manner. Likewise, exposed plants exhibited increased expressions of glutathione synthase and glutathione S-transferase (nearly threefold increase in both roots and leaves), indicating a promising role of thiols in detoxification of TiO2NPs in tomato. The elemental analysis of tissues performed at 0.5, 1, and 2 g/L TiO2NPs indicates that TiO2NPs transport significantly affected the distribution of essential elements (P, S, Mg, and Fe) in roots and leaves displaying about threefold increases in P and 25% decrease in Fe contents. This study presents the mechanistic basis for the differential responses of titanium nanoparticles in tomato, and calls for a cautious approach for the application of nanomaterials in agriculture. GRAPHICAL ABSTRACTMovement of nanotitania in plant tissues.

Accumulation efficiency, genotoxicity and antioxidant defense mechanisms in medicinal plant Acalypha indica L. under lead stress.

The present study was designed to assess the physiological and biochemical changes in roots and shoots of the herb Acalypha indica grown under hydroponic conditions during exposure to lead (Pb) (100-500 mg L-1) for 1-12 d. The accumulation of Pb by A. indica plants was found to be 121.6 and 17.5 mg g-1 dry weight (DW) in roots and shoots, respectively, when exposed to a Pb concentration of 500 mg L-1. The presence of Pb ions in stem, root and leaf tissues was confirmed by scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Concerning the activity of antioxidant enzymes, viz., peroxidase (POX) catalase (CAT) and ascorbate peroxidase (APX), they were induced at various regimes during 5, 8 and 12 d of Pb exposure in both the leaves and roots than untreated controls. Lead treatment increased superoxide dismutase (SOD) activity in both the leaf and root tissues over control, irrespective of the duration of exposure. Anew, it was observed that Pb treatments induced variations in the number and intensity of protein bands. Random amplified polymorphic DNA (RAPD) results show that the Pb treatment caused genotoxicity on DNA molecules as evidenced by the amplification of new bands and the absence of normal DNA amplicons in treated plants. Results confirm that A. indica is a Pb accumulator species, and the antioxidants might play a crucial role in the detoxification of Pb-induced toxic effects.

An overview on manufactured nanoparticles in plants: Uptake, translocation, accumulation and phytotoxicity.

The unprecedented capability to control and characterize materials on the nanometer scale has led to the rapid expansion of nanostructured materials. The expansion of nanotechnology, resulting into myriads of consumer and industrial products, causes a concern among the scientific community regarding risk associated with the release of nanomaterials in the environment. Bioavailability of excess nanomaterials ultimately threatens ecosystem and human health. Over the past few years, the field of nanotoxicology dealing with adverse effects and the probable risk associated with particulate structures <100 nm in size has emerged from the recognized understanding of toxic effects of fibrous and non-fibrous particles and their interactions with plants. The present review summarizes uptake, translocation and accumulation of nanomaterials and their recognized ways of phytotoxicity on morpho-anatomical, physiological, biochemical and molecular traits of plants. Besides this, the present review also examines the intrinsic detoxification mechanisms in plants in light of nanomaterial accumulation within plant cells or parts.

Yucca-derived synthesis of gold nanomaterial and their catalytic potential.

AuNPs ranging in 20 to 300 nm size were synthesized at a room temperature using Yucca filamentosa leaf extract. Diverse nanomaterial morphologies were obtained by varying the extract concentration, reaction pH, and temperature. While low volumes of extract (0.25 and 0.5 mL) induced the formation of microscale Au sheets with edge length greater than 1 µm, high volumes yielded spherical particles ranging from 20 to 200 nm. Varying pH of the solution significantly influenced the particle shape with the production of largely spherical particles at pH 5 to 6 and truncated triangles at pH 2. Separation of multidimensional nanostructures was achieved using a novel method of sucrose density gradient centrifugation. The catalytic function of Yucca-derived AuNPs was demonstrated by degradation of a wastewater dye: methylene blue using spectrophotometric measurements over time. Treatment with Au nanosheets and spheres demonstrated methylene blue degradation approximately 100% greater than the activity in control at 60 min.

Interventional effects of plumbagin on experimental ulcerative colitis in mice.

Plumbagin (1) is a naphthoquinone constituent of plants that have been used in traditional systems of medicine since ancient times. In the present study, the role of 1 was examined on the amelioration of ulcerative colitis, an inflammatory bowel disease that is not curable currently. Plumbagin was tested at a dose of 6-10 mg/kg body weight in acute and chronic disease models. Diseased mice receiving 1 at 8-10 mg/kg demonstrated a significant suppression of disease symptoms in both models. However, body weight loss was not restored in either of the models. Levels of proinflammatory cytokines (TNF-α, IFN-γ, and IL-17) were reduced significantly by 1 in mice suffering from chronic disease, while cytokine levels remained unaffected in mice with acute disease. However, the percentage of inflammatory (CD14+/CD16+) monocytes present in peripheral blood was significantly reduced by >3-fold (p < 0.05) in treatment groups relative to controls in the acute model. Histological evaluations exhibited the restoration of goblet cells, crypts, and the submucosa along with a significant reduction in monocyte aggregation in colon sections from mice receiving treatment with 1. Restoration in colon size was also observed in the treatment groups.

Enhanced organic phosphorus assimilation promoting biomass and shoot P hyperaccumulations in Lolium multiflorum grown under sterile conditions.

Search for plant species - prodigious in P use - is important for both P-sufficient and -deficient conditions. Gulf and Marshall ryegrass (Lolium multiflorum), grown in sterile media containing different organic P substrates (AMP, ATP, GMP, and IHP), exhibited high rates of growth and shoot P concentrations. Growth increase in Gulf was significantly greater on IHP relative to other sources of organic P substrates. Growth was also dependent on an increasing concentration of IHP (0-20 mM) in this cultivar. P accumulations in Gulf exceeded 1% shoot dry weight from IHP, AMP, and ATP-equivalent to the P accrual from equimolar Pi source. Plants supplied with IHP had phytase activity in root extracts comparable to that in Pi-fed plants or control (no P). The extracellular phytase, however, increased by about 100% relative to that observed in root extracts- for both ryegrass cultivars, but there were no significant differences (P < 0.05) between plant groups grown on different substrates (IHP, Pi or control). No significant differences in phosphomonoesterase activities were evident between plant groups supplied with organic P (IHP, G1P) and inorganic source or control. This study establishes the high P-use efficiency in ryegrass, irrespective of P source.

Synthesis of plant-mediated gold nanoparticles and catalytic role of biomatrix-embedded nanomaterials.

Growth of Sesbania seedlings in chloroaurate solution resulted in the accumulation of gold with the formation of stable gold nanoparticles in plant tissues. Transmission electron microscopy revealed the intracellular distribution of monodisperse nanospheres, possibly due to reduction of the metal ions by secondary metabolites present in cells. X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrated a high degree of efficiency for the biotransformation of Au(III) into Au(0) by planttissues. The catalytic function of the nanoparticle-rich biomass was substantiated by the reduction of aqueous 4-nitrophenol (4-NP). This is the first report of gold nanoparticle-bearing biomatrix directly reducing a toxic pollutant, 4-NP.

Role of ethylenediaminetetraacetic acid on lead uptake and translocation by tumbleweed (salsola kali L.).

Tumbleweed plants (Salsola kali L.) grown in agar and liquid media demonstrated a high capacity to accumulate Pb in their different parts without affecting biomass. Whereas shoot elongation and biomass were not significantly affected by high tissue concentrations of Pb, root growth was significantly affected relative to controls. Roots, stems, and leaves demonstrated Pb concentrations of 31,000, 5,500, and 2,100 mg/kg dry weight, respectively, when plants were grown in the agar medium containing 80 mg Pb/L. Application of ethylenediaminetetraacetic acid (EDTA) to Pb-contaminated media dramatically reduced the total acquisition of Pb from both types of media. However, EDTA significantly increased the translocation of Pb from roots to the aerial parts, as evidenced by a multifold increase (23- and 155-fold for agar and liquid media, respectively) in the translocation concentration factor. The concentration of the antioxidant thiol compounds significantly increased (p < 0.05) in plants grown with uncomplexed Pb treatments relative to control plants. Scanning-electron microscopy and electron dispersive x-ray spectroscopic evaluation of leaf samples demonstrated an interesting pattern of Pb translocation in the presence or absence of EDTA. Large Pb crystals were found across the leaf tissues (palisade, spongy parenchyma, and conducting tissues) in the absence of EDTA. Lead nanoparticles also were seen when plants were grown in Pb-EDTA solution. Ultramicroscopic features of tumbleweed provide clear evidence for the unrestricted conduction of Pb from the root to the aerial parts, and this property makes the plant a good candidate for phytoremediation.

Phytoextraction of excess soil phosphorus.

In the search for a suitable plant to be used in P phytoremediation, several species belonging to legume, vegetable and herb crops were grown in P-enriched soils, and screened for P accumulation potentials. A large variation in P concentrations of different plant species was observed. Some vegetable species such as cucumber (Cucumis sativus) and yellow squash (Cucurbita pepo var. melopepo) were identified as potential P accumulators with >1% (dry weight) P in their shoots. These plants also displayed a satisfactory biomass accumulation while growing on a high concentration of soil P. The elevated activities of phosphomonoesterase and phytase were observed when plants were grown in P-enriched soils, this possibly contributing to high P acquisition in these species. Sunflower plants also demonstrated an increased shoot P accumulation. This study shows that the phytoextraction of phosphorus can be effective using appropriate plant species.

Effects of lead and chelators on growth, photosynthetic activity and Pb uptake in Sesbania drummondii grown in soil.

Effects of lead (Pb) and chelators, such as EDTA, HEDTA, DTPA, NTA and citric acid, were studied to evaluate the growth potential of Sesbania drummondii in soils contaminated with high concentrations of Pb. S. drummondii seedlings were grown in soil containing 7.5 g Pb(NO(3))(2) and 0-10 mmol chelators/kg soil for a period of 2 and 4 weeks and assessed for growth profile (length of root and shoot), chlorophyll a fluorescence kinetics (F(v)/F(m) and F(v)/F(o)) and Pb accumulations in root and shoot. Growth of plants in the presence of Pb+chelators was significantly higher (P<0.05) than the controls grown in the presence of Pb alone. F(v)/F(m) and F(v)/F(o) values of treated seedlings remained unaffected, indicating normal photosynthetic efficiency and strength of plants in the presence of chelators. On application of chelators, while root uptake of Pb increased four-five folds, shoot accumulations increased up to 40-folds as compared to controls (Pb only) depending on the type of chelator used. Shoot accumulations of Pb varied from 0.1 to 0.42% (dry weight) depending on the concentration of chelators used.

Characterization of phosphate accumulation in Lolium multiflorum for remediation of phosphorus-enriched soils.

Deterioration in water quality caused by the movement of excessive soil P has created a condition necessary for the development of a sustainable P remediation technology. In this investigation, the phytoremediation potential of Gulf and Marshall ryegrass (Lolium multiflorum) grown in a greenhouse was determined under varying conditions of soil P concentration, pH, and temperature. Both genotypes demonstrated P accumulations > or =1% shoot dry weight depending on soil P concentrations (0-10 g of P/kg of soil), with higher shoot P in Gulf than Marshall ryegrass. An increase in plant biomass was proportional to the increasing concentrations of P up to a level of 10 g of P/kg of soil. The effect of soil pH on plant uptake of P was noticeable with a significant rise in shoot P in acidic soil (pH 5.6) as compared to soil with pH 7.8. Significant differences were observed in the biomass productivity and shoot P accumulation at varying temperatures in both grass types. The patterns of acid phosphomonoesterase and phytase activities in plant roots were interesting, activities being 2-fold higher in alkaline soil than acidic soil in both genotypes. The effect of P supply on the enzyme activity was also distinct, as plants growing in a high P concentration showed higher activity (nearly 30%) than those growing under P deficiency conditions (with no addition of P). These results indicate that Gulf and Marshall ryegrass can accumulate high P under optimal conditions and thus reduce soil P concentrations in successive cropping.

Chemical speciation and cellular deposition of lead in Sesbania drummondii.

The internalized speciation of lead in roots and leaves of Sesbania drummondii, a lead hyperaccumulator, grown in lead nitrate solution was studied using x-ray absorption near-edge structure and extended x-ray absorption fine structure. Lead was predominantly present as lead acetate in both plant tissues. The other dominant forms of accumulation were lead-sulfur compounds. Whereas lead sulfate and sulfide were found in leaves, only lead sulfide was detected in root samples. These observations indicate that S. drummondii is able to biotransform lead nitrate in the nutrient solution to lead acetate and sulfate in its tissues. Complexation with acetate and sulfate may be a lead detoxification strategy in this plant. Transmission-electron microscopy revealed the pattern of lead distribution in and around the cells. Dense distributions of lead grains were detected in root cell walls and plasma membranes, whereas evidence for vacuolar transport of lead was noticed in the stem cells.

Enhanced accumulation of phosphate by Lolium multiflorum cultivars grown in phosphate-enriched medium.

Agricultural and animal husbandry practices combined with soil composition have caused phosphate overloading of farmlands in different parts of the U.S. and Europe. Movement of soluble phosphates (Pi) from phosphorus enriched soils results in degradation of natural aquatic systems, triggering serious environmental problems. Remediation of such sites using plants that tolerate and accumulate high concentrations of Pi in their aerial parts may be an attractive remediation technology. In the present study, Pi transport and accumulation potential of Marshall and Gulf ryegrass (Lolium multiflorum cultivars) were determined using a solution culture of seedlings. Ryegrass seedlings accumulated phosphorus (P) in excess of 2% of dry weight in their aerial parts when supplied with 5 g/L KH2PO4 in medium. Phosphorus accumulation was positively correlated with the concentration of phosphate (0-5 g/L KH2PO4) in medium. Plants grew well on medium containing 5 g/L KH2PO4, but concentrations above 5 g/L caused symptoms of toxicity. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed high P accumulation in different cell types of grass roots and shoots. Phosphate starvation and replenishment experiments point to the unique ability of these grasses to concentrate phosphate in the above-ground parts. It is hypothesized that the unique ability of these ryegrass cultivars may be due to the presence of efficient phosphate transport and sequestration mechanisms.

Antioxidant defense in a lead accumulating plant, Sesbania drummondii.

Seedlings of Sesbania drummondii were grown in 500 mg l-1 Pb(NO3)2 in presence and absence of chelators: EDTA, DTPA and HEDTA for 4 weeks. Plants were assayed for activities of the antioxidant enzymes: ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), superoxide dismutase (SOD) and glutathione (gamma-glutamyl-cysteinyl-glycine) content. Activities of antioxidant enzymes were elevated in the presence of Pb but were similar to controls in plants grown in the presence of Pb and EDTA, -DTPA or -HEDTA. Glutathione content was significantly elevated upon exposure to Pb, but lowered upon exposure to chelators. Chlorophyll a fluorescence kinetics were assessed by determination of Fv/Fm and Fv/Fo values. Seedling growth in Pb alone and Pb + chelators did not significantly affect photosynthetic integrity (Fv/Fo) and efficiency (Fv/Fm). The results suggest that Sesbania plants were able to tolerate Pb-induced stress using an effective antioxidant defense mechanism. This study also indicates a protective role of synthetic chelators in Pb-induced oxidative stress metabolism in a Pb-accumulating plant.

Characterization of a lead hyperaccumulator shrub, Sesbania drummondii.

Lead phytoextraction can be economically feasible only when the developed systems employ high biomass plants that can accumulate greater than 1% Pb in their shoots. In this study Sesbania drummondii, a leguminous shrub occurring in the wild, was used to demonstrate its capability for greater than 1% Pb accumulation in shoots when grown in a Pb-contaminated nutrient solution. Shoot concentrations of >4% Pb were obtained from Sesbania plants grown on modified Hoagland's solution containing 1 g Pb(NO3)2/L. The accumulation of Pb in the tissue was found to be dependent on the concentration of Pb in the nutrient solution. Addition of EDTA (100 microM) in the medium containing 1 g Pb(NO3)2/L increased uptake by 21%. Lower pH also favored Pb translocation to shoot. Results also indicate the path of Pb transport through root tissues. Scanning electron microscopy revealed the distribution of Pb granules in the cells from epidermis to the central axis, indicating both apoplastic and symplastic modes of transport. Transmission electron microscopy and X-ray microanalysis of root sections demonstrated the localization of Pb granules in the plasma membrane and cell wall, and also in the vacuoles. This investigation shows that S. drummondii satisfies the prerequisites for a hyperaccumulator, and thus might be useful, particularly, in the restoration of disturbed vegetation.