TEM image and particle size distribution of TiO₂ NPs.

<p>TEM image and particle size distribution of TiO₂ NPs.</p

Effects of TiO₂ nanoparticles on wheat (<i>Triticum aestivum L</i>.) seedlings cultivated under super-elevated and normal CO₂ conditions

<div><p>Concerns over the potential risks of nanomaterials to ecosystem have been raised, as it is highly possible that nanomaterials could be released to the environment and result in adverse effects on living organisms. Carbon dioxide (CO₂) is one of the main greenhouse gases. The level of CO₂ keeps increasing and subsequently causes a series of environmental problems, especially for agricultural crops. In the present study, we investigated the effects of TiO₂ NPs on wheat seedlings cultivated under super-elevated CO₂ conditions (5000 mg/L CO₂) and under normal CO₂ conditions (400 mg/L CO₂). Compared to the normal CO₂ condition, wheat grown under the elevated CO₂ condition showed increases of root biomass and large numbers of lateral roots. Under both CO₂ cultivation conditions, the abscisic acid (ABA) content in wheat seedlings increased with increasing concentrations of TiO₂ NPs. The indolepropioponic acid (IPA) and jasmonic acid (JA) content notably decreased in plants grown under super-elevated CO₂ conditions, while the JA content increased with increasing concentrations of TiO₂ NPs. Ti accumulation showed a dose-response manner in both wheat shoots and roots as TiO₂ NPs concentrations increased. Additionally, the presence of elevated CO₂ significantly promoted Ti accumulation and translocation in wheat treated with certain concentrations of TiO₂ NPs. This study will be of benefit to the understanding of the joint effects and physiological mechanism of high-CO₂ and nanoparticle to terrestrial plants.</p></div

Physiological responses of wheat seedlings upon exposure to different levels of CO₂.

<p>Values are presented as mean±SD, error bars represent standard deviation (sample size, n = 64 under super-elevated CO₂ condition and n = 48 under normal CO₂ condition). Lower letters represent significant difference at p<0.05 between super-elevated and normal CO₂ treatments.</p

Effects of TiO₂ NPs on seedling biomass and number of lateral roots.

<p>Values are mean±SD, error bars represent standard deviation (sample size, n = 12 for I and II, n = 16 for III, IV and V). Lower letters represent significant difference at p<0.05 among TiO₂ NPs treatments under the same CO₂ conditions; Upper letters represent significant difference at p<0.05 between super-elevated CO₂ and normal CO₂ conditions at the same TiO₂ NPs concentration.</p

Phenotypic images of wheat seedlings in different concentrations of TiO2 NPs treatments with or without super elevated CO₂.

<p>(I) Seedlings grown in different concentrations of TiO₂ NPs under normal CO₂ conditions in a plant growth chamber. (II) Seedlings grown in different concentrations of TiO₂ NPs under super-elevated CO₂ conditions.</p

Effects of TiO₂ NPs on phytohormone contents in wheat seedlings grown under elevated-and normal CO₂ conditions.

<p>Data are mean±SD, error bars represent standard deviation (sample size, n = 16 for treatments under super-elevated CO₂ condition and n = 12 for treatments under normal CO₂ condition). Lower letters represent significant difference at p<0.05 among TiO₂ NPs treatments under the same CO₂ conditions; Upper letters represent significant difference at p<0.05 between elevated CO₂ and normal CO₂ conditions at the same TiO₂ NPs concentration.</p

Chaperonin-Nanocaged Hemin as an Artificial Metalloenzyme for Oxidation Catalysis

Taking inspiration from biology’s effectiveness in functionalizing protein-based nanocages for chemical processes, we describe here a rational design of an artificial metalloenzyme for oxidations with the bacterial chaperonin GroEL, a nanocage for protein folding in nature, by supramolecular anchoring of catalytically active hemin in its hydrophobic central cavity. The promiscuity of the chaperonin cavity is an essential element of this design, which can mimic the hydrophobic binding pocket in natural metalloenzymes to accept cofactor and substrate without requiring specific ligand–protein interactions. The success of this approach is manifested in the efficient loading of multiple monomeric hemin cofactors to the GroEL cavity by detergent dialysis and good catalytic oxidation properties of the resulting biohybrid in tandem with those of the clean oxidant of H₂O₂. Investigation of the mechanism of hemin–GroEL-catalyzed oxidation of two-model substrates reveals that the kinetic behavior of the complex follows a ping-pong mechanism in both cases. Through comparison with horseradish peroxidase, the oxidative activity and stability of hemin–GroEL were observed to be similar to those found in natural peroxidases. Adenosine 5′-triphosphate (ATP)-regulated partial dissociation of the biohybrid, as assessed by the reduction of its catalytic activity with the addition of the nucleotide, raises the prospect that ATP may be used to recycle the chaperonin scaffold. Moreover, hemin–GroEL can be applied to the chromogenic detection of H₂O₂, which (or peroxide in general) is commonly contained in industrial wastes. Considering the rich chemistry of free metalloporphyrins and the ease of production of GroEL and its supramolecular complex with hemin, this work should seed the creation of many new artificial metalloenzymes with diverse reactivities

Phytotoxicity of Silver Nanoparticles to Peanut (<i>Arachis hypogaea</i> L.): Physiological Responses and Food Safety

In the present study, we investigated the effects of silver nanoparticles (Ag NPs) on peanut (<i>Arachis hypogaea</i> L.) at physiological and biochemical levels as well as the impacts on peanut yield and quality. Peanuts were cultivated in sandy soil amended with different doses of Ag NPs (50, 500, and 2000 mg·kg^–1) for 98 days. Physiological parameters including plant biomass, height, grain weight, and yield suggested that Ag NPs could result in severe damages in plant growth. At the biochemical level, Ag NPs did not change the predominant isozymes of each antioxidant enzyme but significantly elevated the amounts of antioxidant isozymes as compared to those of the control, and the antioxidant enzyme activities were consistent with the elevation of isozymes. Ag concentrations exhibited a dose–response fashion in peanut tissues with increasing exposure doses of Ag NPs. The evidence of Ag NPs in the edible portion of peanuts was confirmed by transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDS). Additionally, alteration of the contents of fatty acids in peanut grains upon exposure to different doses of Ag NPs indicated that metal-based NPs could impact crop yield and quality. Taken together, our results suggested that the concerns over how to efficiently and safely apply nanoparticle incorporated products in agriculture and how to control their potential impact on the food safety and food quality should draw more attention as NPs themselves could be taken up by crops and humans exposed to them through food consumption