Effect of copper oxide nanoparticles on two varieties of sweetpotato plants.

Little information is available on the interaction of CuO nanoparticles (nCuO) with tuberous roots. In this study, Beauregard-14 (B-14, low lignin) and Covington (COV, high lignin) sweetpotato varieties were cultivated until maturity in soil amended with nCuO, bulk copper oxide (bCuO) and CuCl2 at 25-125 mg/kg. The Cu treatments had no significant influence on chlorophyll content. Gas exchange parameters were not affected in B-14. In COV, however, at 125 mg/kg treatments, bCuO reduced the intercellular CO2 (11%), while CuCl2 increased it by 7%, compared with control (p ≤ 0.035). At 25 mg/kg nCuO increased the length of COV roots (20.7 ± 2.0 cm vs. 14.6 ± 0.8 cm, p ≤ 0.05). In periderm of B-14, nCuO, at 125 mg/kg, increased Mg by 232%, while the equivalent concentration of CuCl2 reduced P by 410%, compared with control (p ≤ 0.05). The data suggest the potential application of nCuO as nanofertilizer for sweetpotato storage root production.

Long-term assessment of nano and bulk copper compound exposure in sugarcane (Saccharum officinarum).

As interest in the use of copper-based nanomaterials in agriculture continue to increase, research into their exposure effects must expand from short-term, high exposure studies to long-term studies at realistic concentrations. Long-term studies can better elucidate the implications of copper nanomaterial exposure by allowing plants to mature and adapt to higher copper concentrations. In this study, sugarcane plants were grown to maturity in large nursery pots using soils amended with one of the following treatments: Kocide 3000 (Cu(OH)2), a nano-sized CuO (nCuO), a bulk-sized CuO (bCuO), copper metal nanoparticles (Cu NP), or CuCl2 at 20, 40, and 60 mg kg-1. After tissue harvesting, copper content in plant tissues, including pressed cane juice, were determined. Chlorophyll content and the activity of reactive oxygen species (ROS) related enzymes, in root tissues, were measured as an indicator of plant health. Elemental analysis revealed significant changes in root copper concentrations only upon application of the highest levels of Kocide 3000, nCuO, and Cu NP. However, translocation of copper to leaf tissues displayed consistent increases with added copper over controls. Plants treated with Kocide 3000 at 60 mg kg-1 experienced a significant 31% decrease in cane juice yield; copper concentrations in the pressed juice of plants treated with: Kocide 3000 at 20 and 60 mg kg-1, nCuO at 20 and 60 mg kg-1, bCuO at 20 mg kg-1, CuCl2 at 40 mg kg-1, and Cu NP increased by at least 58%. Chlorophyll content remained comparable to controls, and there was a significant 50 to 68% decrease in superoxide dismutase (SOD) activity in plants treated with nCuO, bCuO, Cu NP, and CuCl2. The results indicate that sugarcane plants exposed to the selected copper-based treatments were not adversely affected.

Biochemical and physiological effects of copper compounds/nanoparticles on sugarcane (Saccharum officinarum).

The widespread use of copper based nanomaterials has been accompanied by an increasing interest in understanding their potential risks. It is essential to understand the effects of these nanoparticles on edible crops by performing long-term experiments at relevant exposure concentrations. Sugarcane is the source of 70% of the world's sugar supply and the widespread use of refined sugar and the consumption of raw sugarcane can provide a route for nanoparticles to enter the food supply. In order to evaluate the biochemical and physiological effects of copper nanoparticle exposure, sugarcane was grown for one year in soil amended with 20, 40, and 60 mg/kg of Kocide 3000 (a copper based fungicide), copper metal nanoparticles, micro-sized CuO, and CuCl2. The results show that stress indicators such as catalase and ascorbic peroxidase enzymatic activity in the sugarcane plant were activated by all the copper based materials at different concentrations. Sugarcane plants exposed to nearly all copper treatments showed dosage dependent increases in copper concentrations in root tissues. Translocation of copper to aerial tissues was minimal, with copper concentrations not being significantly different from controls. In addition, Chlorophyll A content was higher in plants treated with Kocide 3000 at 20 and 60 mg/kg, µCuO at 20 mg/kg, and CuCl2 at 20 and 60 mg/kg. To our knowledge, this is the first report on the effects of nano-copper compounds in sugarcane crop.

Two-Photon Microscopy and Spectroscopy Studies to Determine the Mechanism of Copper Oxide Nanoparticle Uptake by Sweetpotato Roots during Postharvest Treatment.

The interaction of engineered nanoparticles with plant tissues is still not well understood. There is a lack of information about the effects of curing (postharvest treatment) and lignin content on copper uptake by sweetpotato roots exposed to copper-based nanopesticides. In this study, Beauregard-14 (lower lignin) and Covington (higher lignin) varieties were exposed to CuO nanoparticles (nCuO), bulk CuO (bCuO), and CuCl2 at 0, 25, 75, and 125 mg/L. Cured and uncured roots were submerged into copper suspensions/solutions for 30 min. Subsequently, root segments were sliced for imaging with a 2-photon microscope, while other root portions were severed into periderm, cortex, perimedulla, and medulla. They were individually digested and analyzed for Cu content by inductively coupled plasma-optical emission spectroscopy. Microscopy images showed higher fluorescence in periderm and cortex of roots exposed to nCuO, compared with bCuO. At 25 mg/L, only bCuO showed higher Cu concentration in the periderm and cortex of Beauregard-14 (2049 mg/kg and 76 mg/kg before curing; 6769 mg/kg and 354 mg/kg after curing, respectively) and in cortex of Covington (692 mg/kg before curing and 110 mg/kg after curing) compared with controls ( p ≤ 0.05). In medulla, the most internal tissue, only Beauregard-14 exposed to 125 mg bCuO/L showed significantly ( p ≤ 0.05) more Cu before curing (17 mg/kg) and after curing (28 mg/kg), compared with control. This research has shown that the 2-photon microscope can be used to determine CuO particles in nondyed plant tissues. The lack of Cu increase in perimedulla and medulla, even in roots exposed to high CuO concentrations (125 mg/L), suggests that nCuO may represent a good alternative to protect and increase the shelf life of sweetpotato roots, without exposing consumers to excess Cu.

Lessons learned: Are engineered nanomaterials toxic to terrestrial plants?

The expansion of nanotechnology and its ubiquitous applications has fostered unavoidable interaction between engineered nanomaterials (ENMs) and plants. Recent research has shown ambiguous results with regard to the impact of ENMs in plants. On one hand, there are reports that show hazardous effects, while on the other hand, some reports highlight positive effects. This uncertainty whether the ENMs are primarily hazardous or whether they have a potential for propitious impact on plants, has raised questions in the scientific community. In this review, we tried to demystify this ambiguity by citing various exposure studies of different ENMs (nano-Ag, nano-Au, nano-Si, nano-CeO2, nano-TiO2, nano-CuO, nano-ZnO, and CNTs, among others) and their effects on various groups of plant families. After scrutinizing the most recent literature, it seems that the divergence in the research results may be possibly attributed to multiple factors such as ENM properties, plant species, soil dynamics, and soil microbial community. The analysis of the literature also suggests that there is a knowledge gap on the effects of ENMs towards changes in color, texture, shape, and nutritional aspects on ENM exposed plants.

Spectroscopic verification of zinc absorption and distribution in the desert plant Prosopis juliflora-velutina (velvet mesquite) treated with ZnO nanoparticles.

The impact of metal nanoparticles (NPs) on biological systems, especially plants, is still not well understood. The aim of this research was to determine the effects of zinc oxide (ZnO) NPs in velvet mesquite (Prosopis juliflora-velutina). Mesquite seedlings were grown for 15 days in hydroponics with ZnO NPs (10 nm) at concentrations varying from 500 to 4000 mg L(-1). Zinc concentrations in roots, stems and leaves were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). Plant stress was examined by the specific activity of catalase (CAT) and ascorbate peroxidase (APOX); while the biotransformation of ZnO NPs and Zn distribution in tissues was determined by X-ray absorption spectroscopy (XAS) and micro X-ray fluorescence (µXRF), respectively. ICP-OES results showed that Zn concentrations in tissues (2102 ± 87, 1135 ± 56, and 628 ± 130 mg kg(-1) d wt in roots, stems, and leaves, respectively) were found at 2000 mg ZnO NPs L(-1). Stress tests showed that ZnO NPs increased CAT in roots, stems, and leaves, while APOX increased only in stems and leaves. XANES spectra demonstrated that ZnO NPs were not present in mesquite tissues, while Zn was found as Zn(II), resembling the spectra of Zn(NO(3))(2). The µXRF analysis confirmed the presence of Zn in the vascular system of roots and leaves in ZnO NP treated plants.