Zinc oxide (ZnO) nanoparticles (nZnO) are among the most commonly used nanoparticles (NPs), and they have been shown to have harmful effects on plants. However, the molecular mechanisms underlying nZnO tolerance and root sensing of NP stresses have not been elucidated. Here, we compared the differential toxic effects of nZnO and Zn 2+ toxicity on plants during exposure and recovery using a combination of transcriptomic and physiological analyses. Although both nZnO and Zn 2+ inhibited primary root (PR) growth, nZnO had a stronger inhibitory effect on the growth of elongation zones, whereas Zn 2+ toxicity had a stronger toxic effect on meristem cells. Timely recovery from stresses is critical for plant survival. Despite the stronger inhibitory effect of nZnO on PR growth, nZnOexposed plants recovered from stress more rapidly than Zn 2+ -exposed plants upon transfer to normal conditions, and transcriptome data supported these results. In contrast to Zn 2+ toxicity, nZnO induced endocytosis and caused microfilament rearrangement in the epidermal cells of elongation zones, thereby repressing PR growth. nZnO also repressed PR growth by disrupting cell wall organization and structure through both physical interactions and transcriptional regulation. The present study provides new insight into the comprehensive understanding and re-evaluation of NP toxicity in plants.

BackgroundMelatonin and serotonin are well-known signaling molecules that mediate multiple physiological activities in plants, including stress defense, growth, development, and morphogenesis, but their underlying mechanisms have not yet been thoroughly elucidated. In this study, we investigated the roles of melatonin and serotonin in modulating plant growth and defense by integrating physiological and transcriptome analyses in Arabidopsis.ResultsModerate concentrations of melatonin and serotonin did not affect primary root (PR) growth but markedly induced lateral root (LR) formation. Both melatonin and serotonin locally induced the expression of the cell-wall-remodeling-related genes LBD16 and XTR6, thereby inducing LR development. Our data support the idea that melatonin and serotonin lack any auxin-like activity. Treatment with 50 μM serotonin significantly improved PSII activity, and the transcriptome data supported this result. Melatonin and serotonin slightly affected glycolysis and the TCA cycle; however, they markedly regulated the catabolism of several key amino acids, thereby affecting carbon metabolism and energy metabolism. Melatonin and serotonin improved iron (Fe) deficiency tolerance by inducing Fe-responsive gene expression.ConclusionsOverall, our results from the physiological and transcriptome analyses reveal the roles of melatonin and serotonin in modulating plant growth and stress responses and provide insight into novel crop production strategies using these two phytoneurotransmitters.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1548-2) contains supplementary material, which is available to authorized users.