Phenolics impart Au(3+)-stress tolerance to cowpea by generating nanoparticles

Bioremediation of Hazardous Wastes Using Green Synthesis of Nanoparticles

Advanced agronomic methods, urbanisation, and industrial expansion contaminate air, water and soil, globally. Agricultural and industrial activities threaten living biota, causing biodiversity loss and serious diseases. Strategies such as bioremediation and physiochemical remediation have not been effectively beneficial at treating pollutants. Metal-based nanoparticles (NPs) such as copper, zinc, silver, gold, etc., in various nanoformulations and nanocomposites are used more and more as they effectively resist the uptake of toxic compounds via plants by facilitating their immobilisation. According to studies, bio-based NP synthesis is a recent and agroecologically friendly approach for remediating environmental waste, which is effective against carcinogens, heavy metal contamination, treating marine water polluted with excessive concentrations of phosphorus, nitrogen and harmful algae, and hazardous dye- and pesticide-contaminated water. Biogenic resources such as bacteria, fungi, algae and plants are extensively used for the biosynthesis of NPs, particularly metallic NPs. Strategies involving green synthesis of NPs are nontoxic and could be employed for commercial scale production. Here, the focus is on the green synthesis of NPs for reduction of hazardous wastes to help with the clean-up process.

Biosynthesis of gold nanoparticles in the fruiting body of enoki mushrooms ( Flammulina velutipes ) under Pb 2+ induction

Fungi can produce many compounds, such as proteins, enzymes, amino acids, and polysaccharides, which are internalised and enriched for metals, and are widely used as reducing and stabilising agents for the biosynthesis of gold nanoparticles (Au NPs). Almost all fungal sources used in the synthesis of the Au NPs are in the form of cell filtrates or mycelial suspensions. However, the culture of cell-free fungal filtrate and mycelium is not comparable to the propagation of fungal substrates in input and operation. Here, we evaluated in vivo biosynthesis of Au NPs in enoki mushrooms (Flammulina velutipes). HAuCl₄ was reduced in the fruiting body of the enoki mushrooms via induction by Pb²⁺ , resulting in the generation of Au NPs. We then employed UV-Vis absorption spectroscopy, Transmission Electron Microscope, and Energy Dispersive Spectrometer to characterise various shapes of the Au NPs. The elemental analysis indicated that the Au NPs were mainly concentrated in organelles of the stalk and cap cells. We also demonstrated that 0.3-0.5 mM HAuCl₄ was the optimal stress treatment concentration based on the changes in physiological indicators of the enoki mushrooms. This work reveals that fungi can be utilised well as nanomaterial bioreactors.

New Green Approaches in Nanoparticles Synthesis: An Overview

Nanotechnology is constantly expanding, with nanomaterials being more and more used in common commercial products that define our modern life. Among all types of nanomaterials, nanoparticles (NPs) occupy an important place, considering the great amount that is produced nowadays and the diversity of their applications. Conventional techniques applied to synthesize NPs have some issues that impede them from being appreciated as safe for the environment and health. The alternative to these might be the use of living organisms or biological extracts that can be involved in the green approach synthesis of NPs, a process that is free of harmful chemicals, cost-effective and a low energy consumer. Several factors, including biological reducing agent concentration, initial precursor salt concentration, agitation, reaction time, pH, temperature and light, can influence the characteristics of biologically synthesized NPs. The interdependence between these reaction parameters was not explored, being the main impediment in the implementation of the biological method on an industrial scale. Our aim is to present a brief review that focuses on the current knowledge regarding how the aforementioned factors can control the size and shape of green-synthesized NPs. We also provide an overview of the biomolecules that were found to be suitable for NP synthesis. This work is meant to be a support for researchers who intend to develop new green approaches for the synthesis of NPs.

Nanomaterials coupled with microRNAs for alleviating plant stress: a new opening towards sustainable agriculture

Plant growth and development is influenced by their continuous interaction with the environment. Their cellular machinery is geared to make rapid changes for adjusting the morphology and physiology to withstand the stressful changes in their surroundings. The present scenario of climate change has however intensified the occurrence and duration of stress and this is getting reflected in terms of yield loss. A number of breeding and molecular strategies are being adopted to enhance the performance of plants under abiotic stress conditions. In this context, the use of nanomaterials is gaining momentum. Nanotechnology is a versatile field and its application has been demonstrated in almost all the existing fields of science. In the agriculture sector, the use of nanoparticles is still limited, even though it has been found to increase germination and growth, enhance physiological and biochemical activities and impact gene expression. In this review, we have summarized the use and role of nanomaterial and small non-coding RNAs in crop improvement while highlighting the potential of nanomaterial assisted eco-friendly delivery of small non-coding RNAs as an innovative strategy for mitigating the effect of abiotic stress.

Indigenous Proline is a Two-Dimensional Safety-Relief Valve in Balancing Specific Amino Acids in Rice under Hexavalent Chromium Stress

This study highlights the roles of different N sources (N starvation [-N], nitrate [+NO₃^-], and ammonium [+NH₄⁺]) in specific amino acids involved in rice proline (Pro) metabolism under hexavalent chromium [Cr(VI)] stress. In treatment with Cr(VI) - N, the content of glutamate (Glu) in shoots was comparable to that of Pro, while the content of Glu in the roots was significantly higher than that of Pro. In case of treatment with Cr(VI) + NO₃^-/NH₄⁺, the content of Glu in both tissues was significantly higher than that of Pro, suggesting that the synthesis of γ-aminobutyric acid and glutathione was most likely involved. Pro synthesis in rice is mainly derived from the Glu pathway rather than the ornithine (Orn) pathway, which is strongly affected by different N sources. The genetic regulation network of Pro metabolism demonstrated a good signal for describing amino acid balance in rice under Cr(VI) stress.

Non-toxicity of nano alumina: A case on mung bean seedlings

Wide use of Al₂O₃ nanoparticles (NPs) leading to their possible escape into environment and their interaction with living organisms demands immediate attention. We evaluated impact of nanoparticulate (Al₂O₃-NPs) and ionic (Al³⁺) forms of aluminium on early seedling growth of Vigna radiata. While Al³⁺ inhibited growth of seedlings, Al₂O₃-NPs did not affect it negatively. Unlike enhancement in proline, malondialdehyde and H₂O₂ levels in roots and shoots induced by Al³⁺, these stress markers remained unaltered by Al₂O₃-NPs. No signs of membrane damage were recorded in roots of seedlings raised in presence of Al₂O₃-NPs; this was witnessed from insignificant electrolyte leakage and Evans blue uptake. Activities of antioxidant enzymes, i.e., superoxide dismustase, catalase, guaiacol peroxidase in root and shoot were enhanced by Al³⁺. However, they were unaffected by Al₂O₃-NPs. Al³⁺ enhanced levels of non-protein thiols, phenolics and ascorbate, with no alterations induced by Al₂O₃-NPs. These findings revealed that, Al₂O₃-NPs did not induce oxidative stress in seedlings. Seedlings raised in Al³⁺ showed higher uptake of Al than those grown in Al₂O₃-NPs; Al content was higher in roots. Al was not detected in shoots of seedlings grown in Al₂O₃-NPs. Lower translocation of Al in seedlings raised in Al₂O₃-NPs was due to adsorption/restriction of Al₂O₃-NPs on root surface. Al³⁺ caused ruptures on root epidermis of seedlings and inhibited root-hair formation, whereas no structural damage was caused by Al₂O₃-NPs. Our findings revealed that while ionic Al is highly toxic, nanoparticulate form of Al is non-toxic to growth of V. radiata.

Engineered nanomaterials for plant growth and development: A perspective analysis

With the overwhelmingly rapid advancement in the field of nanotechnology, the engineered nanomaterials (ENMs) have been extensively used in various areas of the plant system, including quality improvement, growth and nutritional value enhancement, gene preservation etc. There are several recent reports on the ENMs' influence on growth enhancements, growth inhibition as well as certain toxic impacts on plant. However, translocation, growth responses and stress modulation mechanisms of ENMs in the plant systems call for better and in-depth understanding. Herein, we are presenting a comprehensive and critical account of different types of ENMs, their applications and their positive, negative and null impacts on physiological and molecular aspects of plant growth, development and stress responses. Recent reports revealed mixed effects on plants, ranging from enhanced crop yield, epi/genetic alterations, and phytotoxicity, resulting from the ENMs' exposure. Creditable research in recent years has revealed that the effects of ENMs on plants are species specific and are variable among plant species. ENM exposures are reported to trigger free radical formation, responsive scavenging, and antioxidant armories in the exposed plants. The ENMs are also reported to induce aberrant expressions of microRNAs, the key post-transcriptional regulators of plant growth, development and stress-responses of plants. However, these modulations, if judiciously done, may lead to improved plant growth and yield. A better understanding of the interactions between ENMs and plant responses, including their uptake transport, internalization, and activity, could revolutionize crop production through increased disease resistance, nutrient utilization, and crop yield. Therefore, in this review, we are presenting a critical account of the different selected ENMs, their uptake by the plants, their positive/negative impacts on plant growth and development, along with the resultant ENM-responsive post-transcriptional modifications, especially, aberrant miRNA expressions. In addition, underlying mechanisms of various ENM-plant cell interactions have been discussed.

Differential Response of Floating and Submerged Leaves of Longleaf Pondweed to Silver Ions

In this study, we have investigated variations in the potential of floating and submerged leaves of longleaf pondweed (Potamogeton nodosus) to withstand silver ion (Ag+)-toxicity. Both floating and submerged leaves changed clear colorless AgNO3 solutions to colloidal brown in the presence of light. Transmission electron microscopy revealed the presence of distinct crystalline Ag-nanoparticles (Ag-NPs) in these brown solutions. Powder X-ray diffraction pattern showed that Ag-NPs were composed of Ag0 and Ag2O. Photosystem (PS) II efficiency of leaves declined upon exposure to Ag+ with a significantly higher decline in the submerged leaves than in the floating leaves. Similarly, Ag+ treatment caused a significant reduction in the carboxylase activity of the ribulose bisphosphate carboxylase/oxygenase in leaves. The reduction in this carboxylase activity was significantly higher in the submerged than in the floating leaves. Ag+ treatment also resulted in a significant decline in the levels of non-enzymatic and enzymatic antioxidants; the decline was significantly lower in the floating than in submerged leaves. X-ray photoelectron spectroscopy revealed the presence of Ag2O in these leaves. Inductively coupled plasma mass spectrometry analysis revealed a three-fold higher Ag content in the submerged than in floating leaves. Our study demonstrates that floating leaves of longleaf pondweed have a superior potential to counter Ag+-toxicity compared with submerged leaves, which could be due to superior potential of floating leaves to reduce Ag+ to less/non-toxic Ag0/Ag2O-nanoparticles/nanocomplexes. We suggest that modulating the genotype of longleaf pondweed to bear higher proportion of floating leaves would help in cleaning fresh water bodies contaminated with ionic forms of heavy metals.

Cadmium toxicity-induced proline accumulation is coupled to iron depletion

Investigations were conducted to elucidate the key factor behind Cd²⁺-toxicity-induced proline accumulation in Indian mustard (Brassica juncea) by raising seedlings, independently in distilled water (DW) and mineral growth medium (MGM) in the presence of 0-500 μM CdCl₂. Invariably, Cd²⁺-induced toxicity, measured in terms of growth, was significantly more prominent in seedlings raised in DW than those raised in MGM. Cd²⁺ brought about a significant reduction in growth and photosystem II activity with a concomitant increase in proline levels, in a concentration-dependent manner. Interestingly, the level of iron in shoots of seedlings decreased proportionately with increase in Cd²⁺ toxicity. Cd²⁺-promoted proline accumulation was significantly higher in seedlings raised in DW than those raised in MGM. Depletion of essential cations (viz. Ca²⁺, Mg²⁺, K⁺, and Fe²⁺) from MGM one at a time revealed that depletion of Fe²⁺ leads to maximal proline accumulation under Cd²⁺ toxicity. Interestingly, proline level in seedlings raised under Cd²⁺ toxicity in DW supplemented with Fe²⁺ was similar to that recorded in seedlings raised in MGM. Our results convincingly demonstrated that Cd²⁺-induced iron deficiency promotes proline accumulation.

Light Mediated Generation of Silver Nanoparticles by Spinach Thylakoids/Chloroplasts

The unique potential of chloroplasts/thylakoids to harness light energy to transport electrons from H2O to various entities was exploited for reduction of Ag+ to generate nanoparticles (NPs). Spinach thylakoids/chloroplasts turned AgNO3 solutions brown in light, but not in dark. Besides showing Ag-NPs specific surface plasmon resonance band, these brown solutions showed presence of 5-30 nm crystalline NPs composed of Ag. Powder X-ray diffraction (PXRD) analysis revealed that Ag-NPs were biphasic composed of face-centered cubic Ag0 and cubic Ag2O. X-ray photoelectron spectroscopy (XPS) data further corroborated the presence of Ag2O in Ag-NPs. Limited formation of Ag-NPs in dark and increased generation of Ag0/Ag2O-NPs with increase in light intensity (photon flux density) by thylakoids/chloroplasts, established the role of light-harvesting photosynthetic machinery in generation of Ag0/Ag2O-NPs. Potential of thylakoids/chloroplasts to generate Ag-NPs from Ag+ on exposure to red and blue wavelength regions of visible light of electromagnetic spectrum, further confirmed the involvement of photosynthetic electron transport in reduction of Ag+ and generation of Ag-NPs. While light energy mediated photosynthetic electron transport donates energized electrons extracted from H2O to Ag+ to form Ag0-NPs, O2 released as a by-product during photolysis of H2O oxidizes Ag0 to form Ag2O-NPs. Our findings furnish a novel, simple, economic and green method that can be exploited for commercial production of Ag0/Ag2O-NPs.

Engineered Gold Nanoparticles and Plant Adaptation Potential

Use of metal nanoparticles in biological system has recently been recognised although little is known about their possible effects on plant growth and development. Nanoparticles accumulation, translocation, growth response and stress modulation in plant system is not well understood. Plants exposed to gold and gold nanoparticles have been demonstrated to exhibit both positive and negative effects. Their growth and yield vary from species to species. Cytoxicity of engineered gold nanoparticles depends on the concentration, particle size and shape. They exhibit increase in vegetative growth and yield of fruit/seed at lower concentration and decrease them at higher concentration. Studies have shown that the gold nanoparticles exposure has improved free radical scavenging potential and antioxidant enzymatic activities and alter micro RNAs expression that regulate different morphological, physiological and metabolic processes in plants. These modulations lead to improved plant growth and yields. Prior to the use of gold nanoparticles, it has been suggested that its cost may be calculated to see if it is economically feasible.

A rapid, ideal, and eco-friendlier protocol for quantifying proline

Proline, a stress marker, is routinely quantified by a protocol that essentially uses hazardous toluene. Negative impacts of toluene on human health prompted us to develop a reliable alternate protocol for proline quantification. Absorbance of the proline-ninhydrin condensation product formed by reaction of proline with ninhydrin at 100 °C in the reaction mixture was significantly higher than that recorded after its transfer to toluene, revealing that toluene lowers sensitivity of this assay. λ _max of the proline-ninhydrin complex in the reaction mixture and toluene were 508 and 513 nm, respectively. Ninhydrin in glacial acetic acid yielded higher quantity of the proline-ninhydrin condensation product compared to ninhydrin in mixture of glacial acetic acid and H₃PO₄, indicating negative impact of H₃PO₄ on proline quantification. Further, maximum yield of the proline-ninhydrin complex with ninhydrin in glacial acetic acid and ninhydrin in mixture of glacial acetic acid and H₃PO₄ was achieved within 30 and 60 min, respectively. This revealed that H₃PO₄ has negative impact on the reaction rate and quantity of the proline-ninhydrin complex formed. In brief, our proline quantification protocol involves reaction of a 1-ml proline sample with 2 ml of 1.25 % ninhydrin in glacial acetic acid at 100 °C for 30 min, followed by recording absorbance of the proline-ninhydrin condensation product in the reaction mixture itself at 508 nm. Amongst proline quantification protocols known till date, our protocol is the most simple, rapid, reliable, cost-effective, and eco-friendlier.

Reducing strength prevailing at root surface of plants promotes reduction of Ag+ and generation of Ag(0)/Ag2O nanoparticles exogenously in aqueous phase

Potential of root system of plants from wide range of families to effectively reduce membrane impermeable ferricyanide to ferrocyanide and blue coloured 2,6-dichlorophenol indophenol (DCPIP) to colourless DCPIPH₂ both under non-sterile and sterile conditions, revealed prevalence of immense reducing strength at root surface. As generation of silver nanoparticles (NPs) from Ag⁺ involves reduction, present investigations were carried to evaluate if reducing strength prevailing at surface of root system can be exploited for reduction of Ag⁺ and exogenous generation of silver-NPs. Root system of intact plants of 16 species from 11 diverse families of angiosperms turned clear colorless AgNO₃ solutions, turbid brown. Absorption spectra of these turbid brown solutions showed silver-NPs specific surface plasmon resonance peak. Transmission electron microscope coupled with energy dispersive X-ray confirmed the presence of distinct NPs in the range of 5–50 nm containing Ag. Selected area electron diffraction and powder X-ray diffraction patterns of the silver NPs showed Bragg reflections, characteristic of crystalline face-centered cubic structure of Ag⁰ and cubic structure of Ag₂O. Root system of intact plants raised under sterile conditions also generated Ag⁰/Ag₂O-NPs under strict sterile conditions in a manner similar to that recorded under non-sterile conditions. This revealed the inbuilt potential of root system to generate Ag⁰/Ag₂O-NPs independent of any microorganism. Roots of intact plants reduced triphenyltetrazolium to triphenylformazon and impermeable ferricyanide to ferrocyanide, suggesting involvement of plasma membrane bound dehydrogenases in reduction of Ag⁺ and formation of Ag⁰/Ag₂O-NPs. Root enzyme extract reduced triphenyltetrazolium to triphenylformazon and Ag⁺ to Ag⁰ in presence of NADH, clearly establishing potential of dehydrogenases to reduce Ag⁺ to Ag⁰, which generate Ag⁰/Ag₂O-NPs. Findings presented in this manuscript put forth a novel, simple, economically viable and green protocol for synthesis of silver-NPs under ambient conditions in aqueous phase, using root system of intact plants.