New Insights into the Transcriptional, Epigenetic, and Physiological Responses to Zinc Oxide Nanoparticles in Datura stramonium ; Potential Species for Phytoremediation

This study aimed to explore the physiological, epigenetic, and transcriptional responses of Datura stramonium, a stress-resistant plant, to long-time exposure to zinc oxide nanoparticles (nZnO; 0, 100, and 500 mg l−1). The results of the study illustrate that the nZnO100 promoted biomass accumulation and growth indices, whereas nZnO500 caused severe phytotoxicity. Unlike nZnO500 treatment which reduced leaf K (34.7%) and Fe (16.2%), implying impaired nutrition, the nZnO100-treated seedlings encompassed higher concentrations of K (20.8%) and Fe (21.7%) than the control. Moreover, the nZnO displayed a higher efficacy to improve Zn bioaccumulation than the bulk counterpart, and the supplements induced phenylalanine ammonia-lyase, catalase, and peroxidase activities. Besides, nZnO500 treatment enhanced leaf proline concentration. The nZnO treatments also led to variations in the expression of histone deacetylase (HDA3), indicating an epigenetic modification. The nZnO treatments transcriptionally stimulated the WRKY1 transcription factor by an average of 9.5-fold. With increasing the concentration of nZnO, transcriptions of AREB and bZIP transcription factors were induced by averages of 4.3- and 8.7-fold, respectively. The supplements transcriptionally upregulated proteinase inhibitor II (PI-II). While nZnO500 was associated with a drastic induction (11.28-fold) in hyoscyamine 6 beta-hydroxylase (H6H), the nZnO100 treatment slightly (3.2-fold) induced transcription of H6H. The upregulations in the expression of tropinone reductase I (TRI) resulted from the nZnO treatments. Ultimately, positive correlations were found among transcription factors (AREB, bZIP, and WRKY1), H6H, TRI, and PI-II. This study provides deeper insights into the nZnO-associated molecular responses in transcription factors, epigenetics, secondary metabolism, and defense-related genes in resistant plant species.