The exposure of gadolinium at environmental relevant levels induced genotoxic effects in Arabidopsis thaliana (L.)

Rare Earth Elements (REEs) are increasingly being used in agriculture and are also used to produce high end technological devices, thereby increasing their anthropogenic presence in the environment. However, the ecotoxicological mechanism of REEs on organisms is not fully understood. In this study, the effects of gadolinium (Gd) addition on Arabidopsis thaliana (L.) were investigated at both physiological and molecular levels. Four treatments (0, 10, 50 and 200 ?mol.L- 1 Gd) were used in the exposure tests. Biomass, root length and chlorophyll content in shoots/roots were measured to investigate the plant?s physiological response to Gd stress. Random amplified polymorphic (RAPD)-Polymerase Chain Reaction (PCR) and methylation sensitive arbitrarily primed (MSAP)-PCR were used to investigate changes in genetic variation and DNA methylation of A. thaliana when exposed to Gd. At the physiological level, it was found that low concentration of Gd (10 ?mol.L-1) could significantly increase the plant biomass and root length, while the growth of A. thaliana was significantly inhibited when exposed to 200 ?mol.L-1 of Gd, yet the total soluble protein content in aerial plant parts increased significantly by 24.2% when compared to the control group. Among the 12 primers considered in the RAPD assessment, at the molecular level, only four primers revealed different patterns in their genomic DNA. Compared to the control group, the treatment with 50 ?mol.L- 1 of Gd was associated with lower polymorphism, while the treatment with 200 ?mol.L-1 of Gd was associated with higher polymorphism. The polymorphism frequencies for the 50 ?mol.L- 1 of Gd and the 200 ?mol.L- 1 of Gd were 4.67% and 20.33%, respectively. The MSAP analysis revealed that the demethylation (D) type of Arabidopsis genomic DNA increased significantly under 10 and 50 ?mol.L- 1 of Gd, while the methylation (M) type was also significantly increased under 200 ?mol.L- 1 of Gd. Generally, the total methylation polymorphism (D+M) increased with an increase of Gd concentration. It was found that high concentrations of Gd appeared to cause DNA damage, but low concentrations of Gd (as low as 10 ?mol.L-1) were associated with DNA methylation change. Further, it was verified by Real time Reverse Transcription PCR (RT-PCR) on the bands detected by the MSAP analysis, that the genes relative to processes including cell cycle, oxidative stress and apoptosis, appeared to be regulated by methylation under Gd stress. These findings reveal new insight regarding ecotoxicity mechanisms of REEs on plants.

Automated summary

This study investigated the effects of gadolinium (Gd) addition on Arabidopsis thaliana (L.) at both physiological and molecular levels. Results showed that low concentration of Gd could increase plant biomass and root length, while high concentrations of Gd appeared to cause DNA damage. Molecular analysis revealed changes in genetic variation and DNA methylation under Gd stress, suggesting that genes related to cell cycle, oxidative stress, and apoptosis were regulated by methylation. These findings provide new insights into the ecotoxicity mechanisms of rare earth elements on plants.