Exogenous gibberellic acid shortening after-ripening process and promoting seed germination in a medicinal plant Panax notoginseng.

BACKGROUND: Panax notoginseng (Burk) F.H. Chen is an essential plant in the family of Araliaceae. Its seeds are classified as a type of morphophysiological dormancy (MPD), and are characterized by recalcitrance during the after-ripening process. However, it is not clear about the molecular mechanism on the after-ripening in recalcitrant seeds. RESULTS: In this study, exogenous supply of gibberellic acid (GA3) with different concentrations shortened after-ripening process and promoted the germination of P. notoginseng seeds. Among the identified plant hormone metabolites, exogenous GA3 results in an increased level of endogenous hormone GA3 through permeation. A total of 2971 and 9827 differentially expressed genes (DEGs) were identified in response to 50 mg L-1 GA3 (LG) and 500 mg L-1 GA3 (HG) treatment, respectively, and the plant hormone signal and related metabolic pathways regulated by GA3 was significantly enriched. Weighted gene co-expression network analysis (WGCNA) revealed that GA3 treatment enhances GA biosynthesis and accumulation, while inhibiting the gene expression related to ABA signal transduction. This effect was associated with higher expression of crucial seed embryo development and cell wall loosening genes, Leafy Contyledon1 (LEC1), Late Embryogenesis Abundant (LEA), expansins (EXP) and Pectinesterase (PME). CONCLUSIONS: Exogenous GA3 application promotes germination and shorts the after-ripening process of P. notoginseng seeds by increasing GA3 contents through permeation. Furthermore, the altered ratio of GA and ABA contributes to the development of the embryo, breaks the mechanical constraints of the seed coat and promotes the protrusion of the radicle in recalcitrant P. notoginseng seeds. These findings improve our knowledge of the contribution of GA to regulating the dormancy of MPD seeds during the after-ripening process, and provide new theoretical guidance for the application of recalcitrant seeds in agricultural production and storage.

iTRAQ and RNA-seq analyses provide an insight into mechanisms of recalcitrance in a medicinal plant Panax notoginseng seeds during the after-ripening process.

Panax notoginseng (Burk) F.H. Chen is an important economic and medicinal plant from the family of Araliaceae, and its seed is characterised by the recalcitrance and after-ripening process. However, the molecular mechanism on the dehydration sensitivity is not clear in recalcitrant seeds. In the present study, isobaric tag for relative and absolute quantification (iTRAQ) and RNA-seq were used to analyse the proteomic and transcriptomic changes in seeds of P. notoginseng in days after-ripening (DAR). A total of 454 differentially expressed proteins (DEPs) and 12000 differentially expressed genes (DEGs) were obtained. The activity of enzymes related to antioxidant system were significantly increased, and the late embryogenesis abundant (LEA) protein family and most members of glutathione metabolism enzymes have been downregulated during the after-ripening process. The lack or inadequate accumulation of LEA proteins in the embryo and the low activity of antioxidant defense in glutathione metabolism might be the key factors leading to the dehydration sensitivity in recalcitrant seeds of P. notoginseng. In addition, the increased activity of elycolysis (EMP), citric acid cycle (TCA) and pentose phosphate pathway (PPP) pathways might be one of important signals to complete the after-ripening process. Overall, our study might provide a new insight into the molecular mechanism on dehydration sensitivity of recalcitrant seeds.