Understanding the Physiological and Molecular Mechanism of Persistent Organic Pollutant Uptake and Detoxification in Cucurbit Species (Zucchini and Squash)

Cucurbita pepo ssp pepo (zucchini) roots phytoextract significant amounts of persistent organic pollutants (POPs) from soil, followed by effective translocation to aboveground tissues. The closely related C. pepo ssp ovifera (squash) does not have this ability. In a DDE-contaminated field soil, zucchini roots and stems contained 3.6 and 6.6-fold greater contaminant than did squash tissues, respectively, and zucchini phytoextracted 12-times more DDE from soil than squash. In batch hydroponics, squash was significantly more sensitive to DDE (2−20 mg/L) exposure; 4 mg/L DDE significantly reduced squash biomass (14%) whereas for zucchini, biomass reductions were observed at 20 mg/L (20%). PCR select Suppression Subtraction Hybridization was used to identify differentially expressed genes in DDE treated zucchini relative to DDE treated squash or non-treated zucchini. After differential screening to eliminate false positives, unique cDNA clones were sequenced. Out of 40 shoot cDNA sequences, 34 cDNAs have homology to parts of phloem filament protein 1 (PP1). Out of 6 cDNAs from the root tissue, two cDNAs are similar to cytochrome P450 like proteins, and one cDNA matches a putative senescence associated protein. From the DDE exposed zucchini seedlings cDNA library, out of 22 differentially expressed genes, 14 cDNAs were found to have homology with genes involved in abiotic stresses, signaling, lipid metabolism, and photosynthesis. A large number of cDNA sequences were found to encode novel unknown proteins that may be involved in uncharacterized pathways of DDE metabolism in plants. A semiquantitative RT-PCR analysis of isolated genes confirmed up-regulation in response to DDE exposure

Metal-Based Nanotoxicity and Detoxification Pathways in Higher Plants

The potential risks from metal-based nanoparticles (NPs) in the environment have increased with the rapidly rising demand for and use of nanoenabled consumer products. Plant’s central roles in ecosystem function and food chain integrity ensure intimate contact with water and soil systems, both of which are considered sinks for NPs accumulation. In this review, we document phytotoxicity caused by metal-based NPs exposure at physiological, biochemical, and molecular levels. Although the exact mechanisms of plant defense against nanotoxicity are unclear, several relevant studies have been recently published. Possible detoxification pathways that might enable plant resistance to oxidative stress and facilitate NPs detoxification are reviewed herein. Given the importance of understanding the effects and implications of metal-based NPs on plants, future research should focus on the following: (1) addressing key knowledge gaps in understanding molecular and biochemical responses of plants to NPs stress through global transcriptome, proteome, and metablome assays; (2) designing long-term experiments under field conditions at realistic exposure concentrations to investigate the impact of metal-based NPs on edible crops and the resulting implications to the food chain and to human health; and (3) establishing an impact assessment to evaluate the effects of metal-based NPs on plants with regard to ecosystem structure and function

Physiological and Molecular Response of <i>Arabidopsis thaliana</i> (L.) to Nanoparticle Cerium and Indium Oxide Exposure

The effects of cerium oxide (CeO₂) and indium oxide (In₂O₃) nanoparticles (NPs) exposure on <i>Arabidopsis thaliana</i> (L.) Heynh. were investigated. After inoculation in half strength MS medium amended with 0–2000 ppm CeO₂ and In₂O₃ NPs for 25 days, both physiological and molecular responses were evaluated. Exposure at 250 ppm CeO₂ NPs significantly increased plant biomass, but at 500–2000 ppm, plant growth was decreased by up to 85% in a dose-dependent fashion. At 1000 and 2000 ppm CeO₂ NPs, chlorophyll production was reduced by nearly 60% and 85%, respectively, and anthocyanin production was increased 3–5-fold. Malondialdehyde (MDA) production, a measure of lipid peroxidation, was unaffected by exposure to 250–500 ppm CeO₂ NPs, but at 1000 ppm, MDA formation was increased by 2.5-fold. Exposure to 25–2000 ppm In₂O₃ NPs had no effect on <i>A. thaliana</i> biomass and only minor effects (15%) on root elongation. Total chlorophyll and MDA production were unaffected by In₂O₃ NPs exposure. Molecular response to NP exposure as measured by qPCR showed that both types of elements altered the expression of genes central to the stress response such as the sulfur assimilation and glutathione (GSH) biosynthesis pathway, a series of genes known to be significant in the detoxification of metal toxicity in plants. Interestingly, In₂O₃ NPs exposure resulted in a 3.8–4.6-fold increase in glutathione synthase (GS) transcript production, whereas CeO₂ NPs yielded only a 2-fold increase. It seems likely that the significantly greater gene regulation response upon In₂O₃ NPs exposure was directly related to the decreased phytotoxicity relative to CeO₂ treatment. The use of NP rare earth oxide elements has increased dramatically, yet knowledge on fate and toxicity has lagged behind. To our knowledge, this is the first report evaluating both physiological and molecular plant response from exposure to these important nanoparticles

Titanium Dioxide Nanoparticles Alleviate Tetracycline Toxicity to <i>Arabidopsis thaliana</i> (L.)

<i>Arabidopsis thaliana</i> (L.) Heynh. was used as a model plant to investigate the biochemical and molecular response upon coexposures to tetracycline (TC) and titanium oxide nanoparticles (TiO₂ NPs). Results showed that 1 mg/L TC severely reduced <i>A. thaliana</i> biomass by 33.3% as compared with the control; however, the presence of 50 and 100 mg/L TiO₂ NPs alleviated TC toxicity, increasing fresh biomass by 45% and 28%, respectively, relative to the TC alone treatment. The presence of TC notably decreased Ti accumulation in both shoots and roots. Antioxidant enzyme activity, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD), in <i>A. thaliana</i> shoots and roots indicated that TC significantly increased the activity of reactive oxygen species (ROS) scavengers. However, in the coexposure treatments, TiO₂ NPs reduced antioxidant enzyme activity back to the control levels. The relative expression of genes encoding sulfur assimilation and glutathione biosynthesis pathways was separately measured in shoots and roots. Interestingly, the relative expressions of adenylytransferase (APT), adenosine-5′-phosphosulfate reductase (APR), and sulfite reductase (SiR) in the roots across all three treatments (TC alone, TiO₂ NPs alone, and TC × TiO₂ NPs treatment) were 2–3.5-fold higher than the control. The expression of γ-glutamylecysteine synthetase (ECS) and glutathione synthetase (GS) was increased in <i>A. thaliana</i> treated with either TiO₂ NPs or TC alone. At harvest, almost 93% reduction of the pod biomass was evident in the TC alone treatment as compared with the control; however, TiO₂ NPs increased the pod biomass by 300% in the coexposed plants relative to the TC alone treatment. These findings provide important information for understanding the interactions of metal-based NPs and cocontaminants such as antibiotics in plant systems

Tannic acid alleviates bulk and nanoparticle Nd₂O₃ toxicity in pumpkin: a physiological and molecular response

<p>The effect of dissolved organic matter (DOM) on nanoparticle toxicity to plants is poorly understood. In this study, tannic acid (TA) was selected as a DOM surrogate to explore the mechanisms of neodymium oxide NPs (Nd₂O₃ NPs) phytotoxicity to pumpkin (<i>Cucurbita maxima</i>). The results from the tested concentrations showed that 100 mg L⁻¹ Nd₂O₃ NPs were significantly toxic to pumpkin in term of fresh biomass, and the similar results from the bulk particles and the ionic treatments were also evident. Exposure to 100 mg L⁻¹ of Nd₂O₃ NPs and BPs in 1/5 strength Hoagland’s solution not only significantly inhibited pumpkin growth, but also decreased the S, Ca, K and Mg levels in plant tissues. However, 60 mg L⁻¹ TA significantly moderated the observed phytotoxicity, decreased Nd accumulation in the roots, and notably restored S, Ca, K and Mg levels in NPs and BPs treated pumpkin. TA at 60 mg L⁻¹ increased superoxide dismutase (SOD) activity in both roots (17.5%) and leaves (42.9%), and catalase (CAT) activity (243.1%) in the roots exposed to Nd₂O₃ NPs. This finding was confirmed by the observed up-regulation of transcript levels of SOD and CAT in Nd₂O₃ NPs treated pumpkin analyzed by quantitative reverse transcription polymerase chain reaction. These results suggest that TA alleviates Nd₂O₃ BPs/NPs toxicity through alteration of the particle surface charge, thus reducing the contact and uptake of NPs by pumpkin. In addition, TA promotes antioxidant enzymatic activity by elevating the transcript levels of genes involved in ROS scavenging. Our results shed light on the mechanisms underlying the influence of DOM on the bioavailability and toxicity of NPs to terrestrial plants.</p

Reduced Silver Nanoparticle Phytotoxicity in Crambe abyssinica with Enhanced Glutathione Production by Overexpressing Bacterial γ‑Glutamylcysteine Synthase

Silver nanoparticles (Ag NPs) are widely used in consumer products, and their release has raised serious concerns about the risk of their exposure to the environment and to human health. However, biochemical mechanisms by which plants counteract NP toxicity are largely unknown. We have previously engineered Crambe abyssinica plants expressing the bacterial γ-glutamylecysteine synthase (γ-ECS) for enhancing glutathione (GSH) levels. In this study, we investigated if enhanced levels of GSH and its derivatives can protect plants from Ag NPs and AgNO₃ (Ag⁺ ions). Our results showed that transgenic lines, when exposed to Ag NPs and Ag⁺ ions, were significantly more tolerant, attaining a 28%–46% higher biomass and 34–49% more chlorophyll content, as well as maintaining 35–46% higher transpiration rates as compared to those of wild type (WT) plants. Transgenic γ-ECS lines showed 2–6-fold Ag accumulation in shoot tissue and slightly lower or no difference in root tissue relative to levels in WT plants. The levels of malondialdehyde (MDA) in γ-ECS lines were also 27.3–32.5% lower than those in WT Crambe. These results indicate that GSH and related peptides protect plants from Ag nanotoxicity. To our knowledge, this is the first direct report of Ag NP detoxification by GSH in transgenic plants, and these results will be highly useful in developing strategies to counteract the phytotoxicty of metal-based nanoparticles in crop plants

Surface Coated Sulfur Nanoparticles Suppress <i>Fusarium</i> Disease in Field Grown Tomato: Increased Yield and Nutrient Biofortification

Little is known about the effect of nano sulfur (NS) under field conditions as a multifunctional agricultural amendment. Pristine and surface coated NS (CS) were amended in soil at 200 mg/kg that was planted with tomato (Solanum lycopersicum) and infested with Fusarium oxysporum f. sp. lycopersici. Foliar exposure of CS (200 μg/mL) was also included. In healthy plants, CS increased tomato marketable yield up to 3.3∼3.4-fold compared to controls. In infested treatments, CS significantly reduced disease severity compared to the other treatments. Foliar and soil treatment with CS increased yield by 107 and 192% over diseased controls, respectively, and significantly increased fruit Ca, Cu, Fe, and Mg contents. A $33/acre investment in CS led to an increase in marketable yield from 4920 to 11,980 kg/acre for healthy plants and from 1135 to 2180 kg/acre for infested plants, demonstrating the significant potential of this nanoenabled strategy to increase food production

Nanoscale Sulfur Improves Plant Growth and Reduces Arsenic Toxicity and Accumulation in Rice (Oryza sativa L.)

Rice is known to accumulate arsenic (As) in its grains, posing serious health concerns for billions of people globally. We studied the effect of nanoscale sulfur (NS) on rice seedlings and mature plants under As stress. NS application caused a 40% increase in seedling biomass and a 26% increase in seed yield of mature plants compared to untreated control plants. AsIII exposure caused severe toxicity to rice; however, coexposure of plants to AsIII and NS alleviated As toxicity, and growth was significantly improved. Rice seedlings treated with AsIII + NS produced 159 and 248% more shoot and root biomass, respectively, compared to plants exposed to AsIII alone. Further, AsIII + NS-treated seedlings accumulated 32 and 11% less As in root and shoot tissues, respectively, than the AsIII-alone treatment. Mature plants treated with AsIII + NS produced 76, 110, and 108% more dry shoot biomass, seed number, and seed yield, respectively, and accumulated 69, 38, 18, and 54% less total As in the root, shoot, flag leaves, and grains, respectively, compared to AsIII-alone-treated plants. A similar trend was observed in seedlings treated with AsV and NS. The ability of sulfur (S) to alleviate As toxicity and accumulation is clearly size dependent as NS could effectively reduce bioavailability and accumulation of As in rice via modulating the gene expression activity of As transport, S assimilatory, and glutathione synthesis pathways to facilitate AsIII detoxification. These results have significant environmental implications as NS application in agriculture has the potential to decrease As in the food chain and simultaneously enable crops to grow and produce higher yields on marginal and contaminated lands

Time-Dependent and Coating Modulation of Tomato Response upon Sulfur Nanoparticle Internalization and Assimilation: An Orthogonal Mechanistic Investigation

Nanoenabled strategies have recently attracted attention as a sustainable platform for agricultural applications. Here, we present a mechanistic understanding of nanobiointeraction through an orthogonal investigation. Pristine (nS) and stearic acid surface-modified (cS) sulfur nanoparticles (NPs) as a multifunctional nanofertilizer were applied to tomato (Solanum lycopersicumL.) through soil. Both nS and cS increased root mass by 73% and 81% and increased shoot weight by 35% and 50%, respectively, compared to the untreated controls. Bulk sulfur (bS) and ionic sulfate (iS) had no such stimulatory effect. Notably, surface modification of S NPs had a positive impact, as cS yielded 38% and 51% greater shoot weight compared to nS at 100 and 200 mg/L, respectively. Moreover, nS and cS significantly improved leaf photosynthesis by promoting the linear electron flow, quantum yield of photosystem II, and relative chlorophyll content. The time-dependent gene expression related to two S bioassimilation and signaling pathways showed a specific role of NP surface physicochemical properties. Additionally, a time-dependent Global Test and machine learning strategy applied to understand the NP surface modification domain metabolomic profiling showed that cS increased the contents of IA, tryptophan, tomatidine, and scopoletin in plant leaves compared to the other treatments. These findings provide critical mechanistic insights into the use of nanoscale sulfur as a multifunctional soil amendment to enhance plant performance as part of nanoenabled agriculture

Additional file 1 of Meta QTL analysis for dissecting abiotic stress tolerance in chickpea

Supplementary Material