Assessment of Effects of the Long-Term Exposure of Agricultural Crops to Carbon Nanotubes.

Carbon-based nanoparticles (CBNs) are nanomaterials that have been shown to be plant growth regulators. Here, we investigated the effects of long-term exposure to multi-walled carbon nanotubes (MWCNTs) on the growth of three important crops (barley, soybean, and corn). The tested species were cultivated in hydroponics supplemented with 50 µg/mL MWCNTs. After 20 weeks of continuous exposure to the nanomaterials, no significant toxic effects on plant development were observed. Several positive phenotypical changes were recorded, in addition to the enhancement of photosynthesis in MWCNT-exposed crops. Raman spectroscopy with point-by-point mapping proved that the MWCNTs in the hydroponic solution moved into all tested species and were distributed in analyzed organs (leaves, stems, roots, and seeds). Our results confirmed the significant potential of CBN in plant agriculture. However, the documented presence of MWCNTs in different organs of all exposed crops highlighted the importance of detailed risk assessment of nanocontaminated plants moving into the food chain.

Role of carbonaceous nanomaterials in stimulating osteogenesis in mammalian bone cells.

In this work, we demonstrate that graphitic nanomaterials-carboxylated multi-walled carbon nanotubes (MWCNTs) and carboxylated graphenes (Gn)-have the ability to stimulate the process of osteogenesis in mammalian bone cells and significantly increase the level of bone mineralization. Exposure of MC3T3-E1 bone cells to carboxylated MWCNTs-nano-sized (nano-Gn) and micro-sized (micro-Gn) in concentrations of 1-10 µg ml-1-resulted in the enhancement of mineralization in a time-dependent manner for the cells exposed to the nanomaterials, as compared to unexposed cells. However, the graphitic nanomaterials did not show significant toxicity in the concentration levels that were studied. Gene expression analysis revealed that the MWCNTs activated expression of the mid-stage osteogenic marker, Col I, on the 12th day of cell incubation. The gene expression of the earliest osteogenic marker, Cbfa-1, and the downstream effector of BMP signaling, SMAD1, were significantly increased in bone cells exposed to both materials (MWCNTs and nano-Gn) as compared to unexposed control cells. Our data clearly demonstrate the ability of graphitic nano-materials to penetrate bone cells and regulate deposition of minerals in an in vitro model system. Our findings highlight the potential use of such materials in regenerative nanomedicine.

Modification of tomato growth by expression of truncated ERECTA protein from Arabidopsis thaliana.

ERECTA family genes encode leucine-rich repeat receptor-like kinases that control multiple aspects of plant development such as elongation of aboveground organs, leaf initiation, development of flowers, and epidermis differentiation. These receptors have also been implicated in responses to biotic and abiotic stress, probably as a consequence of their involvement in regulation of plant architecture. Here, ERECTA signalling in tomatoes (Solanum lycopersicum) was manipulated by expressing truncated ERECTA protein (AtΔKinase) from Arabidopsis using two different promoters. In Arabidopsis, this protein functions in a dominant-negative manner, disrupting signalling of the whole ERECTA gene family. Expression of AtΔKinase under a constitutive 35S promoter dramatically reduced vegetative growth and led to the formation of fruits with a reduced seed set. Similarly, expression of AtΔKinase under its own promoter resulted in transgenic tomato plants with diminished growth, a reduced number of leaves, changed flowering time, and slightly increased stomata density. The transgenic plants also exhibited increased tolerance to water deficit stress, at least partially due to their diminished surface area. These phenotypes of the transgenic plants were the result of ERECTA signalling disruption at the protein level, as the expression of two endogenous tomato ERECTA family genes was not suppressed. These results demonstrate the significance of ERECTA family genes for development and stress responses in tomato and suggest that truncated ERECTA can be used to manipulate the growth of crop species.

Surface chemistry of carbon nanotubes impacts the growth and expression of water channel protein in tomato plants.

Specific properties of carbon nanotubes, such as their level of agglomeration in the medium and their surface characteristics, can be critical for the physiological response of plants upon application of carbon nanotubes. The correlations among the level of aggregation, the type of functional group on the surface of the carbon nanotubes, and the growth performance of tomato plants are documented.

Carbon nanotubes induce growth enhancement of tobacco cells.

Carbon nanotubes have shown promise as regulators of seed germination and plant growth. Here, we demonstrate that multiwalled carbon nanotubes (MWCNTs) have the ability to enhance the growth of tobacco cell culture (55-64% increase over control) in a wide range of concentrations (5-500 µg/mL). Activated carbon (AC) stimulated cell growth (16% increase) only at low concentrations (5 µg/mL) while dramatically inhibited the cellular growth at higher concentrations (100-500 µg/mL). We found a correlation between the activation of cells growth exposed to MWCNTs and the upregulation of genes involved in cell division/cell wall formation and water transport. The expression of the tobacco aquaporin (NtPIP1) gene, as well as production of the NtPIP1 protein, significantly increased in cells exposed to MWCNTs compared to control cells or those exposed to AC. The expression of marker genes for cell division (CycB) and cell wall extension (NtLRX1) was also up-regulated in cells exposed to MWCNTs compared to control cells or those exposed to activated carbon only.

In vivo plant flow cytometry: a first proof-of-concept.

In vivo flow cytometry has facilitated advances in the ultrasensitive detection of tumor cells, bacteria, nanoparticles, dyes, and other normal and abnormal objects directly in blood and lymph circulatory systems. Here, we propose in vivo plant flow cytometry for the real-time noninvasive study of nanomaterial transport in xylem and phloem plant vascular systems. As a proof of this concept, we demonstrate in vivo real-time photoacoustic monitoring of quantum dot-carbon nanotube conjugates uptake by roots and spreading through stem to leaves in a tomato plant. In addition, in vivo scanning cytometry using multimodal photoacoustic, photothermal, and fluorescent detection schematics provided multiplex detection and identification of nanoparticles accumulated in plant leaves in the presence of intensive absorption, scattering, and autofluorescent backgrounds. The use of a portable fiber-based photoacoustic flow cytometer for studies of plant vasculature was demonstrated. These integrated cytometry modalities using both endogenous and exogenous contrast agents have a potential to open new avenues of in vivo study of the nutrients, products of photosynthesis and metabolism, nanoparticles, infectious agents, and other objects transported through plant vasculature.

Purification of resveratrol, arachidin-1, and arachidin-3 from hairy root cultures of peanut (Arachis hypogaea) and determination of their antioxidant activity and cytotoxicity.

Antioxidant stilbenoids, such as resveratrol, arachidin-1, and arachidin-3, have demonstrated beneficial effects on human health. Although resveratrol is commercially available, arachidin-1 and arachidin-3 are not, resulting in an opportunity to explore purification methods and to confirm biological activity. Recently, Arachis hypogaea hairy root cultures (produced via Agrobacterium rhizogenes-mediated transformation) were reported to secrete stilbenoids into liquid growth media upon elicitation in quantities sufficient for commercial production. The purpose of this study was to purify substantial quantities of resveratrol, arachidin-1, and arachidin-3 from A. hypogaea hairy root cultures using centrifugal partition chromatography (CPC), determine the antioxidant activity of these compounds using the thiobarbituric acid reactive substances (TBARS) assay, and determine the cytotoxicity of the compounds using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In a single run of CPC, resveratrol, arachidin-1, and arachidin-3 were separated to a purity of 97.1%, 97.0%, and 91.8%, respectively. Lipid oxidation was inhibited by a 27 and 7 µM dose for reference standards of resveratrol and arachidin-1, respectively, while oxidation was not inhibited up to a 27 µM dose for reference standard of arachidin-3. Oxidation was inhibited at a 14, 7, and 14 µM doses for CPC-purified resveratrol, arachidin-1, and arachidin-3, respectively. Arachidin-1 and arachidin-3 demonstrated cytotoxicity at 27 and 55 µM in RAW 264.7 and HeLa cell lines, respectively; while resveratrol exhibited no cytotoxicity to either cell line. These results demonstrate the integration of a production and purification system for the manufacturing of A. hypogaea-derived stilbenoids.