Phytotoxicity of multi-walled carbon nanotubes on red spinach (Amaranthus tricolor L) and the role of ascorbic acid as an antioxidant

Abstract

Carbon nanotubes (CNTs) are a novel nanomaterial with wide potential applications; however the adverse effects of CNTs following environmental exposure have recently received significant attention. Herein, we explore the systemic toxicity and potential influence of 0-1000 mg L −1 the multi-walled CNTs on red spinach. CNTs exposed plants exhibited growth inhibition and cell death after 15 days of hydroponic culture.CNTs had adverse effects on root and leaf morphology, as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy detected CNTs in leaves. Biomarkers of nanoparticle toxicity, reactive oxygen species (ROS), and cell damage in the red spinach were greatly increased 15 days post-exposure to CNTs. These effects were reversed when CNTs were supplemented with ascorbic acid (AsA), suggesting a role of ROS in the CNT-induced toxicity and that the primary mechanism of CNTs' toxicity is oxidative stress.

Carbon nanomaterials: production, impact on plant development, agricultural and environmental applications

“…As already described for cell culture experiments (see above and "Impact of SWCNTs on plants" section), induction of oxidative stress, associated with ROS formation, membrane damage, electrolyte leakage, mitochondrial dysfunctions, DNA aberration and cell death, has been characterized as determinant for MWCNT toxicity. This was also noted during seedling development and early growth of red spinach (A. tricolor), rice (O. sativa), lettuce (L. sativa) and cucumber (C. sativus) [119,122,124] and again small seeds were most sensitive (see also "Impact of SWCNTs on plants" section).…”

“…Qualitative methods of CNM detection in plant samples comprise light microscopy, transmission and scanning electron microscopy (TEM and SEM) able to detect carbon nanotubes, fullerenes and graphene particles in plant samples. Light microscopy was used as an easily available technique for visualization of MWCNT aggregates in contact with Arabidopsis (A. thaliana) cell cultures or for the detection of MWCNTs at the root surface of red spinach (A. tricolor) seedlings, grown in CNT-amended nutrient solution [122]. However, light microscopy only allows detection of large CNMs aggregates but not individual CNM particles.…”

“…Accordingly, the potential toxicity of nanoparticles on plants has not yet been widely investigated, and the reported results are frequently descriptive and contradictory with very limited information on the underlying modes of action [117]. Physiological processes potentially affected by interactions with nanomaterials comprise alterations of gene expression [118,119], DNA damage [120,121] and increased formation of ROS [122,123]. A high variability of responses can be observed between different plant species [124,125], various stages of plant ontogenesis [126] and different varieties [127,128].…”

“…Once nanotubes have passed the seed coat, contact with the radicle and other seedling organs is possible. Accordingly, small diameter MWCNTs (<13 nm), present in the germination medium, could penetrate cell walls and were later detected in the roots of wheat (T. aestivum) [159] and red spinach (A. tricolor) seedlings [122]. Wild and Jones [169] demonstrated that MWCNTs with a diameter of 110-170 nm could pierce the epidermal cell wall and thus penetrate up to 4 μm into the cytoplasm of wheat (T. aestvcum) root hairs.…”

Carbon nanotubes: Impacts and behaviour in the terrestrial ecosystem - A review

“…They also caused necrotic lesions of leaf cells/tissues and changes of root and leaf morphology [102]. MWCNTs (10 mg/L) decreased cell dry weight, viability, chlorophyll content and superoxide dismutase (SOD) activity of Arabidopsis thaliana cell suspension [93].…”