Charge, Size, and Cellular Selectivity for Multiwall Carbon Nanotubes by Maize and Soybean

Abstract

Maize (Zea mays) and soybean (Glycine max) were used as model food-chain plants to explore vegetative uptake of differently charged multiwall carbon nanotubes (MWCNTs). Three types of MWCNTs, including neutral pristine MWCNT (p-MWCNT), positively charged MWCNT-NH2, and negatively charged MWCNT-COOH, were directly taken-up and translocated from hydroponic solution to roots, stems, and leaves of maize and soybean plants at the MWCNT concentrations ranging from 10.0 to 50.0 mg/L during 18-day exposures. MWCNTs accumulated in the xylem and phloem cells and within specific intracellular sites like the cytoplasm, cell wall, cell membrane, chloroplast, and mitochondria, which was observed by transmission electron microscopy. MWCNTs stimulated the growth of maize and inhibited the growth of soybean at the exposed doses. The cumulative transpiration of water in maize exposed to 50 mg/L of MWCNT-COOHs was almost twice as much as that in the maize control. Dry biomass of maize exposed to MWCNTs was greater than that of maize control. In addition, the uptake and translocation of these MWCNTs clearly exhibited cellular, charge, and size selectivity in maize and soybean, which could be important properties for nanotransporters. This is the first report of cellular, charge, and size selectivity on the uptake by whole food plants for three differently charged MWCNTs.

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

“…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. MWCNTs taken up by plant roots were even detected in the xylem and in phloem cells [129]. A root to shoot translocation of MWCNTs is most probably driven by transpiration [170] as demonstrated for wheat (T. aestivum) and rapeseed (B. napus) [171].…”

“…max.) seedlings [129]. Challenges related to TEM comprise low contrast between CNMs and plant tissue structures [130,151], a complicated sample preparation and the need for analysis of large numbers of samples.…”

“…The high variability of nanomaterials in terms of chemical composition, size and shape, surface structure, solubility, aggregation and application modes are also factors most likely contributing to the heterogeneity of plant responses reported in the literature [129,130]. Knowledge of the special structural features of nanomaterials determining the adverse effects on living organisms is a pre-requisite for the so called "safe-by-design" approach for a directed design of nanomaterials without negative environmental side effects [131][132][133].…”

Quantitative evaluation of multi-wall carbon nanotube uptake by terrestrial plants

“…As such, CNT exposure to terrestrial plants is likely. CNTs accumulated by crops could bioaccumulated and biomagnify along the food chain, eventually leading to human exposure [8][9][10][11][12][13][14][15]. Since CNTs may pose a significant risk to ecological and human health, it is essential to understand their toxicity, uptake, and translocation of CNTs in plant [8,[16][17][18][19].…”

“…No accumulation was reported in the roots of cabbage [20], carrot [20], cucumber [20], lettuce [20], onion [20], tomato [20], Alfalfa [21] and wheat [21]. However, CNTs uptake by maize [15], soybean [15], pea [11], sunflower [11], tomato [11], wheat [11,12], rapeseed [12] and different plant cells [8-10, 13, 14] was observed. Notably, most of these studies only used qualitative methods such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman spectroscopy [8-10, 13-15, 20, 22-25].…”