Abstract
Dramatic increase in the use of nanoparticles (NPs) in a variety of applications greatly increased the likelihood of the release of NPs into the environment. Zinc oxide nanoparticles (ZnO NPs) are among the most commonly used NPs, and it has been shown that ZnO NPs were harmful to several different plants. We report here the effects of ZnO NPs exposure on biomass accumulation and photosynthesis in Arabidopsis. We found that 200 and 300 mg/L ZnO NPs treatments reduced Arabidopsis growth by ∼20 and 80%, respectively, in comparison to the control. Pigments measurement showed that Chlorophyll a and b contents were reduced more than 50%, whereas carotenoid contents remain largely unaffected in 300 mg/L ZnO NPs treated Arabidopsis plants. Consistent with this, net rate of photosynthesis, leaf stomatal conductance, intercellular CO2 concentration and transpiration rate were all reduced more than 50% in 300 mg/L ZnO NPs treated plants. Quantitative RT-PCR results showed that expression levels of chlorophyll synthesis genes including CHLOROPHYLL A OXYGENASE (CAO), CHLOROPHYLL SYNTHASE (CHLG), COPPER RESPONSE DEFECT 1 (CRD1), MAGNESIUM-PROTOPORPHYRIN IX METHYLTRANSFERASE (CHLM) and MG-CHELATASE SUBUNIT D (CHLD), and photosystem structure gene PHOTOSYSTEM I SUBUNIT D-2 (PSAD2), PHOTOSYSTEM I SUBUNIT E-2 (PSAE2), PHOTOSYSTEM I SUBUNIT K (PSAK) and PHOTOSYSTEM I SUBUNIT K (PSAN) were reduced about five folds in 300 mg/L ZnO NPs treated plants. On the other hand, elevated expression, though to different degrees, of several carotenoids synthesis genes including GERANYLGERANYL PYROPHOSPHATE SYNTHASE 6 (GGPS6), PHYTOENE SYNTHASE (PSY) PHYTOENE DESATURASE (PDS), and ZETA-CAROTENE DESATURASE (ZDS) were observed in ZnO NPs treated plants. Taken together, these results suggest that toxicity effects of ZnO NPs observed in Arabidopsis was likely due to the inhibition of the expression of chlorophyll synthesis genes and photosystem structure genes, which results in the inhibition of chlorophylls biosynthesis, leading to the reduce in photosynthesis efficiency in the plants.
Highlights
Nanoparticles (NPs), known as particulate nanomaterials (NMs), are particle materials with at least one dimension in the nanoscale (1–100 nm)
After 1 month of growth, Zinc oxide nanoparticles (ZnO NPs) treated plants showed an obvious decrease in the rosette size, and the decrease in the rosette sizes were positively related with the concentrations of ZnO NPs applied (Figure 1A), suggesting that ZnO NPs inhibited Arabidopsis growth
Because carotenoids contents were increased slightly in ZnO NPs treated plants, we examined the expression of several genes that have been reported to be involved in carotenoids synthesis, including GERANYLGERANYL PYROPHOSPHATE SYNTHASE 6 (GGPS6), PHYTOENE SYNTHASE (PSY), PHYTOENE DESATURASE (PDS), and ZETA-CAROTENE DESATURASE (ZDS) (Lange and Ghassemian, 2003; Dong et al, 2007; Qin et al, 2007; Rodríguez-Villalón et al, 2009)
Summary
Nanoparticles (NPs), known as particulate nanomaterials (NMs), are particle materials with at least one dimension in the nanoscale (1–100 nm) Because of their particular properties, such as small size, high surface-to-volume ratio and unique physical and chemical properties, the use of NPs in industries and a wide range of consumer products are increasing greatly (Stampoulis et al, 2009). These positive commercial advances have stimulated a rapidly increasing production of engineered NPs, which made nanotechnologies a rapidly developing field with an expectation that the annual value of nanotechnologyrelated products is going to reach one trillion dollars in 2015 (Roco, 2005). Whereas silver NPs (Ag NPs) and zinc oxide NPs (ZnO NPs) treatment lead to increase in contents of free radicals, including reactive oxygen and nitrogen species (ROS/RNS) and hydrogen peroxide (H2O2) in duckweed (Thwala et al, 2013)
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