Genotoxicity effects of silver nanoparticles on wheat (Triticum aestivum L.) root tip cells

https://doi.org/10.1016/j.ecoenv.2018.02.069Get rights and content

Highlights

  • Genotoxicity effects of silver nanoparticles on wheat root tip cells were studied.

  • Highest dose of AgNPs caused nuclear erosion and elongation.

  • Increase of AgNPs duration and concentration decreased the number of dividing cells.

  • Increased dose exposure, decreased the number of cells undergoing mitosis.

  • Mitotic abnormalities increased and mitotic index decreased by AgNPs treatments.

Abstract

The distribution and use of nanoparticles have rapidly increased over recent years, but the available knowledge regarding their mode of action, ecological tolerance and biodegradability remains insufficient. Wheat (Triticum aestivum L.) is the most important crop worldwide. In the current study, the effects of silver nanoparticles (AgNPs) obtained from two different sources, namely, green and chemical syntheses, on chromosomal aberrations and cell division were investigated. Wheat root tips were treated with four different AgNP concentrations (10, 20, 40 and 50 ppm) for three different exposure durations (8, 16 and 24 h), and the different concentrations of the nanoparticles were added to the tested grains until the root lengths reached 1.5–2 cm. For each concentration, the mitotic indexes (%) were obtained from an analysis of ~ 2000 cells. The treated root-tip cells exhibited various types of chromosomal aberrations, such as incorrect orientation at metaphase, chromosomal breakage, metaphasic plate distortion, spindle dysfunction, stickiness, aberrant movement at metaphase, fragmentation, scattering, unequal separation, scattering, chromosomal gaps, multipolar anaphase, erosion, and distributed and lagging chromosomes. These results demonstrate that the root tip cells of wheat can readily internalize the AgNPs and that the internalized AgNPs can interfere with the cells’ normal function.

Introduction

Nanoparticles (NPs) are zero-dimensional, 1- and 100-nm crystallites that behave as a single unit regarding their transport and properties. Nanoparticles have a wide range of commercial applications; in fact, silver NPs (AgNPs) are used to produce more than 250 products worldwide (Jiang et al., 2012). NPs can be derived from both natural and anthropogenic sources (Biswas and Wu, 2005, Nowack and Bucheli, 2007, Tervonen et al., 2009) and exert cytotoxic and genotoxic effects in plants, including lipid peroxidation, decreases in the mitotic index (MI), and enhancement of the micronuclei and chromosomal aberration indexes (Kumari et al., 2011).

Different NPs have distinct effects on root growth, which also vary among plant species. Moreover, certain NPs, such as CuO NPs, can cause extensive DNA damage in some agricultural and grassland plants (Rodriguez et al., 2011). Similarly, Manosij et al. (2016) observed a loss of membrane integrity, increased chromosome aberrations, micronucleus formation, DNA strand breaks, and cell cycle arrest at the G2/M checkpoint in Allium cepa following exposure to ZnO nanoparticles (diameter = ∼ 85 nm). In Vicia faba and Nicotiana tabacum, NPs increased intracellular ROS production, lipid peroxidation, and antioxidant enzyme activities (Manosij et al., 2016). The NPs were internalized, leading to notable alterations in cell morphology.

A study of the interaction between AgNPs and V. faba revealed an NP size- and exposure-dependent effect on the MI and chromosomal aberrations (Abdel-Azeem and Elsayed, 2013). Additionally, decreases in the nanoparticle size were associated with decreases in the MI and root growth values with increasing treatment time (h) and increases in the numbers of aberrant cells. Several changes in mitosis, such as disturbed chromosomes at metaphase and anaphase, laggards, fragments, bridges, chromosome stickiness and micronuclei (Mn), were observed. Similarly, Yin et al. (2012) reported that AgNPs have different toxicities based on their size and shape, which can affect cell wall penetration (Morones et al., 2005, Carlson et al., 2008).

Several studies have revealed the ecotoxicity of AgNPs. In fact, AgNPs reduce cell growth, photosynthesis, and chlorophyll production in a marine diatom (Thalassiosira weissflogii) and in fresh water algae (Chlamydomonas reinhardtii), and these toxic effects might be due to the release of dissolved silver upon dissolution of the AgNPs (Navarro et al., 2008a, Navarro et al., 2008b, Miao et al., 2009). Kumari et al. (2011) reported that AgNPs cause impairments in various stages of cell division and cell disintegration in the root tips of onion.

Moreover, Patlolla et al. (2012) demonstrated that exposure to AgNPs significantly increases the numbers of chromosomal aberrations and micronuclei and decreases the MI compared with the control, and Mazumdar (2014) recently revealed that once AgNPs enter cells of Vigna radiata and Brassica campestris, it can cause damage to vacuoles and cell wall integrity and likely affect other organelles. Additionally, the observed retardation of growth during the seedling stage was due to considerable absorption of by the root cells. With an increase in the concentration of AgNPs (up to 60 mg/ml), those particles penetrated the cell wall and damaged the cell morphology and its structural features of Oryza sativa plants (Mirzajani et al., 2013).

Sequentially, the present investigation explored the effects of AgNPs on the MI and chromosomal aberrations in wheat root tips.

Section snippets

Materials and methods

Root tips of wheat (Triticum aestivum L.) (2n = 42) were used as the study material. Ten healthy grains were grown in a Petri dish (7.5 cm) at room temperature, and distilled water was added to each cultivar until germination (two days). Three different exposure times (8, 16 and 24 h) and four AgNP concentrations (10, 20, 40 and 50 ppm in a total volume of 20 ml of dH2O) were tested. The nanoparticles were added to the grains until the root length reached 1.5–2 cm, and for each NP solution, the

Results and discussion

The control wheat root tips showed all mitotic stages (Fig. 3). Approximately 1838 ± 170.04 cells were observed, and most of these were in prophase (665 ± 13.14 cells), followed by metaphase (286 ± 14.71 cells), anaphase (216 ± 2.94 cells), and telophase (107 ± 5.71 cells). The data showed that (564 ± 67.94 cells) were in interphase, and the MI was 69.66 ± 5.09%. No abnormal stages were observed.

Conclusions

In this work, silver nanoparticles applied to root tip cells of wheat (Triticum aestivum L.) were shown genotoxicity effects. Increased nuclear content and elongation as irregular abnormalities, which causing damage to the cell wall and nucleus content, were reported. Nuclear erosion and elongation were found with the exposure to the highest dose of AgNPs for the longest duration resulting in damage to the cell wall. On the other hand, increase in the duration and concentration of AgNP

Acknowledgments

The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding this Research group no. RG 1435-011.

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