Impact of nano-CuO stress on rice (Oryza sativa L.) seedlings

Can CuO nanoparticles lead to epigenetic regulation of antioxidant enzyme system?

Copper has been used from ancient time in various applications. Scientists have exploited its means of exposure and consequences to living organisms. The peculiar property of nanomaterials that is a high surface to volume ratio has increased the range of application in products. Copper oxide nanoparticles (CuO NPs) are widely used in industrial applications such as semiconductor devices, gas sensor, batteries, solar energy converter, microelectronics, heat transfer fluids and consumer products. In contrast, acute toxicity of CuO NPs has also been reported. Subsequently, human and environmental health may be at a high risk. Their frequent use can also contaminate ecosystems. Therefore, the toxicity of CuO NPs needs to be thoroughly understood. In this review, we have tried to discuss the recent facts and mechanism that have been explored for CuO NPs-induced toxicity at a cellular, in vivo and ecotoxicological level. Accordingly, the main cause for induction of toxicity by CuO NPs is the generation of reactive oxygen species (ROS) followed by the mitochondrial destruction that leads to apoptosis via the intrinsic pathway or under the condition such as hypoxia cell on exposure to CuO NPs may commit to necrosis. Moreover, CuO NPs also result in activation of MAPK pathways, ERKs and JNK/SAPK thus play an important role in the activation of AP-1. Furthermore, CuO NPs also leads to up-regulation of p53 and caspase three genes. Therefore, careful measures are required to explore omic technology to understand the molecular mechanism of the deleterious effects caused by CuO NPs. Copyright © 2016 John Wiley & Sons, Ltd.

CuO Nanoparticle Interaction with Arabidopsis thaliana: Toxicity, Parent-Progeny Transfer, and Gene Expression

CuO nanoparticles (NPs) (20, 50 mg L(-1)) inhibited seedling growth of different Arabidopsis thaliana ecotypes (Col-0, Bay-0, and Ws-2), as well as the germination of their pollens and harvested seeds. For most of growth parameters (e.g., biomass, relative growth rate, root morphology change), Col-0 was the more sensitive ecotype to CuO NPs compared to Bay-0 and Ws-2. Equivalent Cu(2+) ions and CuO bulk particles had no effect on Arabidopsis growth. After CuO NPs (50 mg L(-1)) exposure, Cu was detected in the roots, leaves, flowers and harvested seeds of Arabidopsis, and its contents were significantly higher than that in CuO bulk particles (50 mg L(-1)) and Cu(2+) ions (0.15 mg L(-1)) treatments. Based on X-ray absorption near-edge spectroscopy analysis (XANES), Cu in the harvested seeds was confirmed as being mainly in the form of CuO (88.8%), which is the first observation on the presence of CuO NPs in the plant progeny. Moreover, after CuO NPs exposure, two differentially expressed genes (C-1 and C-3) that regulated root growth and reactive oxygen species generation were identified, which correlated well with the physiological root inhibition and oxidative stress data. This current study provides direct evidence for the negative effects of CuO NPs on Arabidopsis, including accumulation and parent-progeny transfer of the particles, which may have significant implications with regard to the risk of NPs to food safety and security.

Insights into the proteomic response of soybean towards Al₂O₃, ZnO, and Ag nanoparticles stress

Understanding the complex mechanisms involved in plant response to nanoparticles is indispensable in assessing the impact of nano-pollutants on environment. The present study compares the phytotoxicity of three different metal-based nanoparticles (Al2O3, ZnO, and Ag) in soybean seedling at proteome level. Plant growth, rigidity of roots, and root cell viability were markedly affected by ZnO- and Ag-NPs stress; while, Al2O3-NPs challenged soybean maintained normal seedling growth like control. Moreover, severe oxidative burst was evident in ZnO-NPs and Ag-NPs treatments. Gel-free proteomic analysis of NPs stressed soybean roots revealed 104 commonly changed proteins primarily associated with secondary metabolism, cell organization, and hormone metabolism. Oxidation-reduction cascade related genes, such as GDSL motif lipase 5, SKU5 similar 4, galactose oxidase, and quinone reductase were up-regulated in Al2O3-NPs challenged roots and down-regulated in ZnO- and Ag-NPs treatments. In comparison to root, 16 common proteins were found to be significantly changed in leaves of NPs exposed soybean that were predominantly associated to photosystem and protein degradation. The proteomic findings suggest that high abundance of proteins involved in oxidation-reduction, stress signaling, hormonal pathways related to growth and development might be the principal key for optimum growth of soybean under Al2O3-NPs stress.

Application of liquid chromatography/electrospray ionization ion trap tandem mass spectrometry for the evaluation of global nucleic acids: methylation in garden cress under exposure to CuO nanoparticles

RATIONALE

A full understanding of the biological impact of nanomaterials demands analytical procedures suitable for the detection/quantification of epigenetic changes that occur in the exposed organisms. Here, the effect of CuO nanoparticles (NPs) on global methylation of nucleic acids in Lepidium sativum was evaluated by liquid chromatography/ion trap mass spectrometry. Enhanced selectivity toward cytosine-containing nucleosides was achieved by using their proton-bound dimers formed in positive electrospray ionization (ESI(+)) as precursor ions for multiple reaction monitoring (MRM) quantification based on one or two ion transitions.

METHODS

Plants were exposed to CuO NPs (0-1000 mg L(-1)); nucleic acid extracts were washed with bathocuproine disulfate; nucleosides were separated on a Luna C18 column coupled via ESI(+) to an AmaZon SL mass spectrometer (Bruker Daltonics). Cytidine, 2´-deoxycytidine, 5-methylcytidine, 5-methyl-2´-deoxycytidine and 5-hydroxymethyl-2´-deoxycytidine were quantified by MRM based on MS(3) ([2M+H](+)/[M+H](+)/[M+H-132](+) or [M+H-116](+)) and MS(2) ([2M+H](+)/[M+H](+) ).

RESULTS

Bathocuproine disulfate, added as Cu(I) complexing agent, allowed for elimination of [2M+Cu](+) adducts from the mass spectra. Poorer instrumental detection limits were obtained for MS(3) (20-120 fmol) as compared to MS(2) (9.0-41 fmol); however, two ion transitions helped to eliminate matrix effects in plant extracts. The procedure was tested by analyzing salmon sperm DNA (Sigma) and applied for the evaluation of DNA and RNA methylation in plants; in the absence of NPs, 13.03% and 0.92% methylated cytosines were found in DNA and RNA, respectively; for NPs concentration >50 mg L(-1), DNA hypomethylation was observed with respect to unexposed plants. RNA methylation did not present significant changes upon plant exposure; 5-hydroxymethyl-2´-deoxycytidine was not detected in any sample.

CONCLUSIONS

The MRM quantification proposed here of cytosine-containing nucleosides using their proton-bound homo-dimers as precursor ions proved its utility for the assessment of global methylation of DNA and RNA in plants under stress imposed by CuO NPs. Detection of copper adducts with cytosine-containing ions, and their elimination by washing extracts with Cu(I) chelator, calls for further investigation.

Plant Responses to Nanoparticle Stress

With the rapid advancement in nanotechnology, release of nanoscale materials into the environment is inevitable. Such contamination may negatively influence the functioning of the ecosystems. Many manufactured nanoparticles (NPs) contain heavy metals, which can cause soil and water contamination. Proteomic techniques have contributed substantially in understanding the molecular mechanisms of plant responses against various stresses by providing a link between gene expression and cell metabolism. As the coding regions of genome are responsible for plant adaptation to adverse conditions, protein signatures provide insights into the phytotoxicity of NPs at proteome level. This review summarizes the recent contributions of plant proteomic research to elaborate the complex molecular pathways of plant response to NPs stress.

Nitric oxide ameliorates zinc oxide nanoparticles-induced phytotoxicity in rice seedlings

Nitric oxide (NO) has been found to function in enhancing plant tolerance to various environmental stresses. However, role of NO in relieving zinc oxide nanoparticles (ZnO NPs)-induced phytotoxicity remains unknown. Here, sodium nitroprusside (SNP, a NO donor) was used to investigate the possible roles and the regulatory mechanisms of NO in counteracting ZnO NPs toxicity in rice seedlings. Our results showed that 10 μM SNP significantly inhibited the appearance of ZnO NP toxicity symptoms. SNP addition significantly reduced Zn accumulation, reactive oxygen species production and lipid peroxidation caused by ZnO NPs. The protective role of SNP in reducing ZnO NPs-induced oxidative damage is closely related to NO-mediated antioxidant system. A decrease in superoxide dismutase activity, as well as an increase in reduced glutathione content and peroxidase, catalase and ascorbate peroxidase activity was observed under SNP and ZnO NPs combined treatments, compared to ZnO NPs treatment alone. The relative transcript abundance of corresponding antioxidant genes exhibited a similar change. The role of NO in enhancing ZnO NPs tolerance was further confirmed by genetic analysis using a NO excess mutant (noe1) and an OsNOA1-silenced plant (noa1) of rice. Together, this study provides the first evidence indicating that NO functions in ameliorating ZnO NPs-induced phytotoxicity.

Copper nanoparticles/compounds impact agronomic and physiological parameters in cilantro (Coriandrum sativum)

The environmental impacts of Cu-based nanoparticles (NPs) are not well understood. In this study, cilantro (Coriandrum sativum) was germinated and grown in commercial potting mix soil amended with Cu(OH)2 (Kocide and CuPRO), nano-copper (nCu), micro-copper (μCu), nano-copper oxide (nCuO), micro-copper oxide (μCuO) and ionic Cu (CuCl2) at either 20 or 80 mg Cu per kg. In addition to seed germination and plant elongation, relative chlorophyll content and micro and macroelement concentrations were determined. At both concentrations, only nCuO, μCuO, and ionic Cu, showed statistically significant reductions in germination. Although compared with control, the relative germination was reduced by ∼50% with nCuO at both concentrations, and by ∼40% with μCuO, also at both concentrations, the difference among compounds was not statistically significant. Exposure to μCuO at both concentrations and nCu at 80 mg kg(-1) significantly reduced (p≤ 0.05) shoot elongation by 11% and 12.4%, respectively, compared with control. Only μCuO at 20 mg kg(-1) significantly reduced (26%) the relative chlorophyll content, compared with control. None of the treatments increased root Cu, but all of them, except μCuO at 20 mg kg(-1), significantly increased shoot Cu (p≤ 0.05). Micro and macro elements B, Zn, Mn, Ca, Mg, P, and S were significantly reduced in shoots (p≤ 0.05). Similar results were observed in roots. These results showed that Cu-based NPs/compounds depress nutrient element accumulation in cilantro, which could impact human nutrition.

Seed priming with polyethylene glycol regulating the physiological and molecular mechanism in rice (Oryza sativa L.) under nano-ZnO stress

The present study was designed to highlight the impact of seed priming with polyethylene glycol on physiological and molecular mechanism of two cultivars of Oryza sativa L. under different levels of zinc oxide nanorods (0, 250, 500 and 750 mg L(-1)). Plant growth parameters were significantly increased in seed priming with 30% PEG under nano-ZnO stress in both cultivars. Whereas, this increase was more prominent in cultivar Qian You No. 1 as compared to cultivar Zhu Liang You 06. Significant increase in photosynthetic pigment with PEG priming under stress. Antioxidant enzymes activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) as well as malondialdehyde (MDA) contents were significantly reduced with PEG priming under nano-ZnO stress. Gene expression analysis also suggested that expression of APXa, APXb, CATa, CATb, CATc, SOD1, SOD2 and SOD3 genes were down regulated with PEG priming as compared to non-primed seeds under stress. The ultrastructural analysis showed that leaf mesophyll and root cells were significantly damaged under nano-ZnO stress in both cultivars but the damage was prominent in Zhu Liang You 06. However, seed priming with PEG significantly alleviate the toxic effects of nano-ZnO stress and improved the cell structures of leaf and roots in both cultivars.

Nanoscale copper in the soil-plant system - toxicity and underlying potential mechanisms

Nanoscale copper particles (nano-Cu) are used in many antimicrobial formulations and products for their antimicrobial activity. They may enter deliberately and/or accidentally into terrestrial environments including soils. Being the major 'eco-receptors' of nanoscale particles in the terrestrial ecosystem, soil-microbiota and plants (the soil-plant system) have been used as a model to dissect the potential impact of these particles on the environmental and human health. In the soil-plant system, the plant can be an indirect non-target organism of the soil-associated nano-Cu that may in turn affect plant-based products and their consumers. By all accounts, information pertaining to nano-Cu toxicity and the underlying potential mechanisms in the soil-plant system remains scanty, deficient and little discussed. Therefore, based on some recent reports from (bio)chemical, molecular and genetic studies of nano-Cu versus soil-plant system, this article: (i) overviews the status, chemistry and toxicity of nano-Cu in soil and plants, (ii) discusses critically the poorly understood potential mechanisms of nano-Cu toxicity and tolerance both in soil-microbiota and plants, and (iii) proposes future research directions. It appears from studies hitherto made that the uncontrolled generation and inefficient metabolism of reactive oxygen species through different reactions are the major factors underpinning the overall nano-Cu consequences in both the systems. However, it is not clear whether the nano-Cu or the ion released from it is the cause of the toxicity. We advocate to intensify the multi-approach studies focused at a complete characterization of the nano-Cu, its toxicity (during life cycles of the least-explored soil-microbiota and plants), and behavior in an environmentally relevant terrestrial exposure setting. Such studies may help to obtain a deeper insight into nano-Cu actions and address adequately the nano-Cu-associated safety concerns in the 'soil-plant system'.

Effects of engineered iron nanoparticles on the bryophyte, Physcomitrella patens (Hedw.) Bruch & Schimp, after foliar exposure

The effects of iron nanoparticles on bryophytes (Physcomitrella patens) were studied following foliar exposure. We used iron nanoparticles (Fe-NP) representative of industrial emissions from the metallurgical industries. After a characterization of iron nanoparticles and the validation of nanoparticle internalization in cells, the effects (cytotoxicity, oxidative stress, lipid peroxidation of membrane) of iron nanoparticles were determined through the axenic culturing of Physcomitrella patens exposed at five different concentrations (5 ng, 50 ng, 500 ng, 5 µg and 50 µg per plant). Following exposure, the plant health, measured as ATP concentrations, was not impacted. Moreover, we studied oxidative stress in three ways: through the measure of reactive oxygen species (ROS) production, through malondialdehyde (MDA) production and also through glutathione regulation. At concentrations tested over a short period, the level of ROS, MDA and glutathione were not significantly disturbed.

Study on the correlation between copper oxide nanoparticles induced growth suppression and enhanced lignification in Indian mustard (Brassica juncea L.)

In this study, the morphological, physiological and molecular level effects of copper oxide nanoparticles (CuONPs) were studied in an economically important oil seed crop Brassica juncea L. The possible involvement of lignification on shoot-root growth retardation was also studied. The seedlings were exposed to 0, 20, 50, 100, 200, 400 and 500mg/L of CuONPs in semi-solid half strength Murashige and Skoog medium under controlled growth chamber conditions for 14 days. Exposure to CuONPs resulted in suppression of shoot-growth, reduction in total chlorophyll and carotenoids contents as well modification of root system architecture such as shortening of primary and lateral roots. Significant increases in hydrogen peroxide formation, peroxidase enzyme activity and lignification of shoots and roots were observed. The lipid peroxidation levels increased significantly in shoots and roots of B. juncea seedlings. Phloroglucinol-HCl staining revealed enhanced lignification of shoot and roots. Gene expression studies revealed significant activation of CuZn superoxide dismutase (CuZnSOD) in roots at all concentrations of CuONPs exposure. In shoots significant up-regulation of CuZnSOD gene was observed upon exposure to 100, 200 and 400 mg/L of CuONPs exposure. However no change in the expression levels of MnSOD gene was observed in both stem and roots. The expression of catalase (CAT) and ascorbate peroxidase (APX) genes were also not changed in shoots. However, significant inhibition of CAT and APX genes were observed in roots of B. juncea plants under exposure to 100, 200, 400 and 500 mg/L of CuONPs exposure. The SOD enzyme activity significantly increased in roots under exposure to 50-500 mg/L of CuONPs and in shoots as a result of exposure to 100-500 mg/L of CuONPs. The APX activity significantly decreased in roots upon exposure to 50-500 mg/L of CuONPs. In shoots, the APX activity significantly decreased upon exposure to 200-500 mg/L of CuONPs.

Nano-CuO and interaction with nano-ZnO or soil bacterium provide evidence for the interference of nanoparticles in metal nutrition of plants

The expansion of nanotechnology raises concerns about the consequences of nanomaterials in plants. Here, the effects of nanoparticles (NPs; 100-500 mg/kg) on processes related to micronutrient accumulation were evaluated in bean (Phaseolus vulgaris) exposed to CuO NPs, a mixture of CuO and ZnO (CuO:ZnO) NPs, and in CuO NP-exposed plants colonized by a root bacterium, Pseudomonas chlororaphis O6 (PcO6) in a sand matrix for 7 days. Depending on exposure levels, the inhibition of growth by CuO NPs was more apparent in roots (10-66 %) than shoots (9-25 %). In contrast, CuO:ZnO NPs or root colonization with PcO6 partially mitigated growth inhibition. At 500 mg/kg exposure, CuO NPs increased soluble Cu in the growth matrix by 23-fold, relative to the control, while CuO:ZnO NPs increased soluble Cu (26-fold), Zn (127-fold) and Ca (4.5-fold), but reduced levels of Fe (0.8-fold) and Mn (0.75-fold). Shoot accumulations of Cu (3.8-fold) and Na (1-fold) increased, while those of Fe (0.4-fold), Mn (0.2-fold), Zn (0.5-fold) and Ca (0.5-fold) were reduced with CuO NP (500 mg/kg) exposure. CuO:ZnO NPs also increased shoot Cu, Zn and Na levels, while decreasing that of Fe, Mn, Ca and Mg. Root colonization reduced shoot uptake of Cu and Na, 15 and 24 %, respectively. CuO NPs inhibited ferric reductase (up to 49 %) but stimulated cupric (up to 273 %) reductase activity; while CuO:ZnO NPs or root colonization by PcO6 altered levels of ferric, but not copper reductase activity, relative to CuO NPs. Cu ions at the level released from the NPs did not duplicate these effects. Our findings demonstrate that in addition to the apparent phytotoxic effects of NPs, NP exposure may also have subtle impacts on secondary processes such as metal nutrition.

Toxicity and translocation of graphene oxide in Arabidopsis thaliana

We investigated the possible safety property and translocation of graphene oxide (GO) in the range of μg/L in Arabidopsis. GO exposure did not obviously influence germination, seed development, shoot and root development of seedlings, and flowering time. Meanwhile, GO exposure could not induce severe H2O2 production, increase in malondialdehyde content, formation of oxidative stress, and altered activities of antioxidant enzymes. Moreover, GO exposure did not change expression patterns of examined genes required for germination, photomorphogenesis, root development, and transition from vegetative to reproductive development. In the seedling, we did not observe severe GO accumulation in mesophyll and parenchyma cells of leaf or stem, and in sieve element in leaf, stem, or root. In contrast, we observed the severe GO accumulation in root hair and root parenchyma cells. Our results provide the physiological basis for safety property of GO at the examined concentrations in Arabidopsis plants. Furthermore, our data imply that although GO was absorbed by Arabidopsis plants through root hairs, plants might still have strong ability to be against GO translocation into stem or leaves. In addition, we found that cotyledon might serve as an important site for GO distribution during the early development.

A mechanistic study on the toxic effect of copper oxide nanoparticles in soybean (Glycine max L.) root development and lignification of root cells

Copper oxide nanoparticles (CuONPs) are widely used in several products and their release into the environment can cause toxicity to major food crops. In this study, toxic responses as a result of CuONPs exposure were studied in soybean (Glycine max L.) seedlings. The plants were grown in 1/2 strength Murashige and Skoog medium containing 0, 50, 100, 200, 400, and 500 mg/L of CuONPs in a growth chamber at 26 ± 2 °C with 16/8 h light/dark photoperiod for 14 days. The toxic effects of CuONPs were tested on the shoot and root development, total chlorophyll content, hydrogen peroxide generation, peroxidase (POD) enzyme activity, and lignification of root cells. The mRNA expression of different genes involved in lignin biosynthesis viz. phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD), peroxidase 2 (POD2), peroxidase 4 (POD4), and peroxidase 7 (POD7) was studied using real-time polymerase chain reaction. Exposure to 500 mg/L of CuONPs significantly reduced the shoot growth, weight, and total chlorophyll content. However, the root length and fresh weights were significantly reduced at all concentrations of CuONPs exposure. Exposure to 100, 200, 400, and 500 mg/L of CuONPs significantly increased the hydrogen peroxide level, POD activity, and lignin contents of roots. Treatment with 2,7-dichlorofluorescein diacetate indicated a concentration-dependent increase in reactive oxygen species generation in roots. Staining with phloroglucinol-HCl revealed a concentration dependant increase in lignification of root cells. The expression levels of PAL, C4H, and CAD genes were significantly up-regulated upon exposure to 100, 200, and 400 mg/L of CuONPs. Significant up-regulation in the expression levels of POD2 and POD4 genes was observed upon exposure to 100, 200, 400, and 500 mg/L of CuONPs. Exposure to 200, 400, and 500 mg/L of CuONPs resulted in significant up-regulation of POD7 gene. These results for the first time show that exposure to CuONPs causes enhanced lignification of root cells and thereby affect root development in soybean seedlings.

SELDI-TOF MS-based discovery of a biomarker in Cucumis sativus seeds exposed to CuO nanoparticles

Metal oxide nanoparticles (NPs) can inhibit plant seed germination and root elongation via the release of metal ions. In the present study, two acute phytotoxicity tests, seed germination and root elongation tests, were conducted on cucumber seeds (Cucumis sativus) treated with bulk copper oxide (CuO) and CuO NPs. Two concentrations of bulk CuO and CuO NPs, 200 and 600ppm, were used to test the inhibition rate of root germination; both concentrations of bulk CuO weakly inhibited seed germination, whereas CuO NPs significantly inhibited germination, showing a low germination rate of 23.3% at 600ppm. Root elongation tests demonstrated that CuO NPs were much stronger inhibitors than bulk CuO. SELDI-TOF MS analysis showed that 34 proteins were differentially expressed in cucumber seeds after exposure to CuO NPs, with the expression patterns of at least 9 proteins highly differing from those in seeds treated with bulk CuO and in control plants. Therefore, these 9 proteins were used to identify CuO NP-specific biomarkers in cucumber plants exposed to CuO NPs. A 5977-m/z protein was the most distinguishable biomarker for determining phytotoxicity by CuO NPs. Principal component analysis (PCA) of the SELDI-TOF MS results showed variability in the modes of inhibitory action on cucumber seeds and roots. To our knowledge, this is the first study to demonstrate that the phytotoxic effect of metal oxide NPs on plants is not caused by the same mode of action as other toxins.

Impact of copper oxide nanoparticles exposure on Arabidopsis thaliana growth, root system development, root lignificaion, and molecular level changes

The effect of copper oxide nanoparticles (CuONPs) on physiological and molecular level responses were studied in Arabidopsis thaliana. The seedlings were exposed to different concentrations of CuONPs (0, 0.5, 1, 2, 5, 10, 20, 50, and 100 mg/L) for 21 days in half strength Murashige and Skoog medium. The plant biomass significantly reduced under different concentrations (2, 5, 10, 20, 50, and 100 mg/L) of CuONPs stress. Exposure to 2, 5, 10, 20, 50, and 100 mg/L of CuONPs has resulted in significant reduction of total chlorophyll content. The anthocyanin content significantly increased upon exposure to 10, 20, 50, and 100 mg/L of CuONPs. Increased lipid peroxidation was observed upon exposure to 5, 10, and 20 mg/L of CuONPs and amino acid proline content was significantly high in plants exposed to 10 and 20 mg/L of CuONPs. Significant reduction in root elongation was observed upon exposure to 0.5-100 mg/L of CuONPs for 21 days. Exposure to CuONPs has resulted in retardation of primary root growth, enhanced lateral root formation, and also resulted in loss of root gravitropism. Staining with phloroglucionol detected the deposition of lignin in CuONPs-treated roots. Histochemical staining of leaves and roots of CuONPs-exposed plants with nitroblue tetrazolium and 3'3'-diaminobenzidine showed a concentration-dependant increase in superoxide and hydrogen peroxide formation in leaves and roots of CuONPs-exposed plants. Cytotoxicity was observed in root tips of CuONPs-exposed plants as evidenced by increased propidium iodide staining. Real-time PCR analysis showed significant induction of genes related to oxidative stress responses, sulfur assimilation, glutathione, and proline biosynthesis under CuONPs stress.

Effect of silver nanoparticles on rice (Oryza sativa L. cv. KDML 105) seed germination and seedling growth

With the advances in nanotechnology, silver nanoparticles (AgNPs) have been applied in many industries, increasing their potential exposure level in the environment, yet their environmental safety remains poorly evaluated. The possible effects of different sized AgNPs (20, 30-60, 70-120 and 150nm diameter) on jasmine rice, Oryza sativa L. cv. KDML 105, were investigated at different concentrations (0.1, 1, 10, 100 and 1000mg/L) upon seed germination and seedling growth. The results revealed that the level of seed germination and subsequent growth of those seedlings that germinated were both decreased with increasing sizes and concentrations of AgNPs. Based on the analysis of AgNPs accumulation in plant tissues, it implied that the higher uptake was found when the seeds were treated with the smaller AgNPs, 20nm diameter AgNPs, but it was trapped in the roots rather than transported to the leaves. These resulted in the less negative effects on seedling growth, when compared to the seed soaking with the larger AgNPs with 150nm diameter. The negative effects of AgNPs were supported by leaf cell deformation when rice seeds were treated with 150-nm-diameter AgNP at the concentration of 10 or 100mg/L during seed germination. These results further strengthen our understanding of environmental safety information with respect to nanomaterials.