The Promotive and Repressive Effects of Exogenous HO on Arabidopsis Seed Germination and Seedling Establishment Depend on Application Dose

Hydrogen peroxide (HO) displays significant and dual effects on seed germination and seedling development, depending on the application dosage. However, the definition of HO thresholds and the mechanisms underlying the dual actions in Arabidopsis seed germination and seedling development are not yet clear. Here, we analyzed the Arabidopsis seed germination profiles in response to different concentrations of exogenous HO and found that 2 mM functions as the key threshold, above this threshold, both seed germination and seedling establishment were gradually inhibited. By RNA-seq analysis and function verification, we identified pathways of abscisic acid (ABA) signalling, seed post-ripening, energy metabolism, ROS homeostasis, and cell wall loosening play positive roles in seed germination and seedling establishment downstream of the HO signalling. Further physio-chemical approaches revealed that exogenous HO affected the accumulation and distribution of O and HO in embryonic tissues by regulating the tissue-specific expression of SDH2-3, RHD2, and PRXs. Collectively, we found that germination rate and aerial growth were positively correlated with endogenous HO content and root length was positively correlated with O accumulation, demonstrating that different ROS signals played specific functions in different tissues and development processes. On the other hand, excessive HO (10 mM) represses these two processes for radicle cell damage caused by oxidation stress. Finally, we put forward the mechanism model of the dual effects of exogenous HO on seed germination and seedling establishment.