Nontoxic mesoporous silica nanoparticles protect Physcomitrium patens against salt stress

Mosses play a crucial role in environmental protection, ecological preservation, and horticulture. While the effects of nanomaterials on angiosperms have been widely studied, their impact on bryophytes remains underexplored. In this study, we investigated the effects of mesoporous silica nanoparticles (MSNs) and virus-like mesoporous silica nanoparticles (VMSNs) on the model moss species Physcomitrium patens (P. patens). Our results revealed that MSNs, with an average size of approximately 123 nm, are nontoxic to P. patens and enhance its salt tolerance. The expression of key genes involved in stress responses were significantly induced in MSN-treated plants under salt stress, including peroxidase (POX), L-ascorbate oxidase (L-AO), alternative oxidase (AOX), and calcium-dependent protein kinase (CPK). MSN treatment reduced the accumulation of H₂O₂ and O₂^·-, increased Ca²⁺ signaling, and modulated reactive oxygen species (ROS) homeostasis, collectively improving moss tolerance to salt stress. MSNs were observed on the cell surface, in intercellular space, and within the cytosol and vesicles. They were transported bidirectionally between rhizoids and apical leaves. This study provides novel insights into the distribution, transport, and functional mechanisms of MSNs in mosses, offering a valuable foundation for the application of nanomaterials in plant stress biology and ecological management of bryophytes.