RESUMEN
The release of silver nanoparticles (AgNPs) in the environment has raised concerns about their effects on living organisms, including plants. In this study, changes in gene expression in Arabidopsis thaliana exposed to polyvinylpyrrolidone-coated AgNPs and silver ions (Ag(+)) were analyzed using Affymetrix expression microarrays. Exposure to 5 mg/L AgNPs (20 nm) for 10 days resulted in upregulation of 286 genes and downregulation of 81 genes by reference to nonexposed plants. Exposure to 5 mg/L Ag(+) for 10 days resulted in upregulation of 84 genes and downregulation of 53 genes by reference to nonexposed plants. Many genes differentially expressed by AgNPs and Ag(+) were found to be involved in the response of plants to various stresses: upregulated genes were primarily associated with the response to metals and oxidative stress (e.g., vacuolar cation/proton exchanger, superoxide dismutase, cytochrome P450-dependent oxidase, and peroxidase), while downregulated genes were more associated with response to pathogens and hormonal stimuli [e.g., auxin-regulated gene involved in organ size (ARGOS), ethylene signaling pathway, and systemic acquired resistance (SAR) against fungi and bacteria]. A significant overlap was observed between genes differentially expressed in response to AgNPs and Ag(+) (13 and 21% of total up- and downregulated genes, respectively), suggesting that AgNP-induced stress originates partly from silver toxicity and partly from nanoparticle-specific effects. Three highly upregulated genes in the presence of AgNPs, but not Ag(+), belong to the thalianol biosynthetic pathway, which is thought to be involved in the plant defense system. Results from this study provide insights into the molecular mechanisms of the response of plants to AgNPs and Ag(+).
Asunto(s)
Arabidopsis/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Nanopartículas del Metal/toxicidad , Plata/toxicidad , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Biomasa , Perfilación de la Expresión Génica , Análisis de Secuencia por Matrices de OligonucleótidosRESUMEN
Three hydroxylated derivatives of PCBs, 2'-hydroxy-4-chlorobiphenyl (2'-OH-4-CB), 3'-hydroxy-4-chlorobiphenyl (3'-OH-4-CB), and 4'-hydroxy-4-chlorobiphenyl (4'-OH-4-CB), were transformed by the PCB degrader, Burkholderia xenovorans. When the bacterium was growing on biphenyl (biphenyl pathway-inducing conditions), all three hydroxylated isomers were transformed. However, only 2'-OH-4-CB was transformed by the bacterium growing on succinate (conditions non-inductive of the biphenyl pathway). Gene expression analyses showed a strong induction of key genes of the biphenyl pathway (bph) when cells were grown on biphenyl, which is consistent with the transformation of the three isomers by biphenyl-grown cells. When cells were grown on succinate, only exposure to 2'-OH-4-CB resulted in expression of biphenyl pathway genes, which suggests that this isomer was capable of inducing the biphenyl pathway. These results provide the first evidence that bacteria are able to metabolize PCB derivatives hydroxylated on the non-chlorinated ring.