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

TEM image and particle size distribution of TiO₂ NPs.

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

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