Plant peptide hormone phytosulfokine promotes embryogenic development of calli in Pinus massoniana

Abstract Pinus massoniana is a critical afforestation and ecological tree species in China. However, the continued existence of this pine is severely threatened by pine wilt disease. Somatic embryogenesis serves as a highly efficient clonal propagation approach. Although significant progress has been made in somatic embryogensis research on P.massoniana, resulting in the successful regeneration of plants, the limited embryogenic potential of improved cell lines and the loss of embryogenic properties resulting from prolonged proliferation have posed obstacles to the industrialization of SE production. Here, we investigated the effect of phytosulfokine on embryogenic development of cell lines from P. massoniana, and then leading to a cascade of physicochemical changes. Eight embryogenic cell lines of P. massoniana were used as research materials to observe phenotype and cytological changes. Physiological factors and the contents of nutrients and endogenous hormones were measured before and after phytosulfokine addition. We found that PSK promoted the embryogenic suspensor mass structure of embryogenic cell lines of P. massoniana. In addition, PSK accumulated soluble sugar, protein, and starch, and maintained redox homeostasis during the cell line proliferation process by reducing H2O2 levels. Further, endogenous hormone indole-3-acetic acid may be the main driver of the embryonic changes of cell lines. Our findings increase our understanding of how PSK affects somatic embryogensis in P. massoniana, thereby providing a valuable tool for establishing efficient somatic embryogensis systems in conifer species.