Effect of nano-hydroxyapatite and phosphate on thorium toxicity - Arabidopsis transcriptomic study

Thorium (Th) is a ubiquitous element but elevated concentrations caused by anthropogenic or natural activities pose health and environmental risks. Plants may be exposed accidentally or during the remediation of contaminated sites. Therefore, in this study, we analyzed the effect of thorium on Arabidopsis plants by RNA-seq profiling. Since Th and phosphorus form insoluble phosphates, we focused on the effect of Th in the presence/ absence of phosphate in wild-type and mutants with altered phosphate management. Furthermore, we investigated the effect of hydroxyapatite nanoparticles, which are considered as material for in situ remediation, on Th toxicity. The highest number of DEGs was recorded in the combination of P absence and Th presence while the lowest in the presence of Th together with hydroxyapatite. Besides a high number of genes involved in stress response, Th also induced the transcription of genes involved in response to P starvation, indicating that Th decreased the availability of P. P deficiency caused by Th contributed to the phytotoxic effect of Th. We observed that nano-hydroxyapatite significantly reduced Th toxicity. Nano-hydroxyapatite also served as a source of inorganic P for the plants, but caused deficiency of essential metals indicated by up-regulation of genes involved in their acquisition.