In this study, the phytotoxicity of seven metal oxide nanoparticles(NPs)—titanium dioxide (nTiO₂), silicon dioxide (nSiO₂), cerium dioxide (nCeO₂), magnetite (nFe₃O₄), aluminum oxide (nAl₂O₃), zinc oxide (nZnO) and copper oxide (nCuO)—was assessed on two agriculturally significant crop plants (maize and rice). The results showed that seed germination was not affected by any of the seven metal oxide NPs. However, at the concentration of 2000 mg·L⁻¹, the root elongation was significantly inhibited by nCuO (95.73% for maize and 97.28% for rice), nZnO (50.45% for maize and 66.75% for rice). On the contrary, minor phytotoxicity of nAl₂O₃ was only observed in maize, and no obvious toxic effects were found in the other four metal oxide NPs. By further study we found that the phytotoxic effects of nZnO, nAl₂O₃ and nCuO (25 to 2000 mg·L⁻¹) were concentration dependent, and were not caused by the corresponding Cu²⁺, Zn²⁺ and Al³⁺ ions (0.11 mg·L⁻¹, 1.27 mg·L⁻¹ and 0.74 mg·L⁻¹, respectively). Furthermore, ZnO NPs (<50 nm) showed greater toxicity than ZnO microparticles(MPs)(<5 μm) to root elongation of both maize and rice. Overall, this study provided valuable information for the application of engineered NPs in agriculture and the assessment of the potential environmental risks.

Rice (Oryza sativa L.), a major staple food for billions of people, was assessed for its phytotoxicity of copper oxide nanoparticle (CuO NPs, size < 50 nm). Under hydroponic condition, seven days of exposure to 62.5, 125, and 250 mg/L CuO NPs significantly suppressed the growth rate of rice seedlings compared to both the control and the treatment of supernatant from 250 mg/L CuO NP suspensions. In addition, physiological indexes associated with antioxidants, including membrane damage and antioxidant enzyme activity, were also detected. Treatment with 250 mg/L CuO NPs significantly increased malondialdehyde (MDA) content and electrical conductivity of rice shoots by 83.4% and 67.0%, respectively. The activity of both catalase and superoxide dismutase decreased in rice leaves treated with CuO NPs at the concentration of 250 mg/L, while the activity of the superoxide dismutase significantly increased by 1.66 times in rice roots exposed to 125 mg/L CuO NPs. The chlorophyll, including chlorophyll a and chlorophyll b, and carotenoid content in rice leaves decreased with CuO NP exposure. Finally, to explain potential molecular mechanisms of chlorophyll variations, the expression of four related genes, namely, Magnesium chelatase D subunit, Chlorophyll synthase, Magnesium-protoporphyrin IX methyltransferase, and Chlorophyllide a oxygenase, were quantified by qRT-PCR. Overall, CuO NPs, especially at 250 mg/L concentration, could affect the growth and development of rice seedlings, probably through oxidative damage and disturbance of chlorophyll and carotenoid synthesis.

The APETALA2/Ethylene Responsive Factor (AP2/ERF) gene family has been shown to play a crucial role in plant growth and development, stress responses and secondary metabolite biosynthesis. Nevertheless, little is known about the gene family in ginseng ( Panax ginseng ), an important traditional medicinal herb in Asia and North America. Here, we report the systematic analysis of the gene family present in ginseng using several transcriptomic databases. A total of 189 putative AP2/ERF genes, defined as PgERF001 through PgERF189 . The 93 PgERF genes that have the complete AP2 domain in their open reading frames were classified into five subfamilies, DREB, ERF, AP2, RAV and Soloist. The DREB subfamily and ERF subfamily were further clustered four and six groups, respectively, compared to the 12 groups of these subfamilies found in Arabidopsis. Gene ontology categorized these 397 transcripts of the 189 PgERF genes into eight functional subcategories, suggesting their functional differentiation and they have been especially enriched for the nucleic acid binding transcription factor activity subcategory. The expression activity and networks of the 397 PgERF transcripts have substantially diversified across tissues, developmental stages and genotypes. Then, the expression change of six PgERF genes randomly selected from DREB subfamily, i.e., PgERF073 , PgERF079 , PgERF110 , PgERF115 , PgERF120 and PgERF128 responding to cold stress suggesting that DREB subfamily genes played an important role in cold resistance of ginseng. Finally, we studied the responses of the PgERF genes to methyl jasmonate (MeJA). 288 (72.5%) of the 397 PgERF gene transcripts responded to the MeJA treatment, with 136 up-regulated and 152 down-regulated, indicating that most members of the PgERF gene family are responsive to MeJA. These results provide resources and knowledge necessary for family-wide functional analysis of the PgERF genes in ginseng and related species.