Abstract
BackgroundKorean pine seeds have primary dormancy following dispersal, leading to poor seed germination and seedling establishment. Metabolic homeostasis determines whether the seeds are dormant or non-dormant. However, the specific metabolic pathways that maintain the primary dormancy of pine seeds are poorly understood.ResultsMetabolic analysis was employed on the embryos of PDRS (seeds released from primary dormancy) and PDS (primary dormant seeds) on days 0, 5 and 11 after incubation under a germination-inductive temperature. A larger metabolic switch occurred in PDRS embryos from days 0 to 11. The contents of ninety metabolites were significantly changed from days 0 to 5, 83% of which (including most sugars, organic acids and amino acids) increased, reflecting that biosynthetic metabolism processes are initiated. The contents of ninety-two metabolites showed distinct variations from days 5 to 11, 71% of which (including most organic acids and almost all amino acids) reduced substantially. Fructose 6-phosphate, inositol-3-phosphate, 3-phosphoglyceric and D-glucose-6-phosphate contents showed the most decrease with decreasing 409-, 75-, 58- and 41-fold, indicating that the glycolysis and tricarboxylic acid (TCA) cycle strongly slowed down. The contents of the most metabolites in PDS embryos also displayed a relatively larger alteration only from days 0 to 5. Although 64% of metabolites increased from days 0 to 5, their levels were still lower compared with PDRS embryos. Furthermore, most metabolites were not further accumulated from days 5 to 11. Unlike PDRS embryos, almost all amino acids in PDS embryos did not exhibit a substantial decrease from days 5 to 11. Also, there was not a major decrease in the levels of metabolites involved mainly in glycolysis and TCA cycle, while some intermediates even increased.ConclusionsThe attenuated biosynthetic metabolism processes, the lower utilization rate of amino acids and the higher operation rate of glycolysis and TCA in embryos maintain primary dormancy.
Highlights
Korean pine seeds have primary dormancy following dispersal, leading to poor seed germination and seedling establishment
A clear formation of six distinct groups (PDRS, 5-day incubated seeds released from primary dormancy (PDRS5), 11-day incubated seeds released from primary dormancy (PDRS11), primary dormant seeds (PDS), 5-day incubated primary dormant seeds (PDS5) and 11-day incubated primary dormant seeds (PDS11)) was observed in the principal component analysis (PCA) score plot (Fig. 2). Both the PDRS5 and PDRS11 samples were discriminated from the seeds released from primary dormancy (PDRS) along the first principal component
The maximum separation occurred between the PDRS5 and PDRS11 groups along the first principal component
Summary
Korean pine seeds have primary dormancy following dispersal, leading to poor seed germination and seedling establishment. The specific metabolic pathways that maintain the primary dormancy of pine seeds are poorly understood. MBKPFs have high plant diversity and play a vital, but poorly understood, role in ecosystem services (e.g., water conservation). Seed dormancy is defined as when an intact viable seed cannot complete germination when it is put under favorable conditions for germination [7]. Song and Zhu BMC Plant Biology (2019) 19:550 dormancy is gradually released, the range of conditions over which seeds complete germination progressively widens [8]. The germination process generally includes three phases: phase I is the process of rapid water absorption by the seed (imbibition), phase II is the process of reactivation of metabolism (lag), and phase III is the stage during which some part of the embryo protrudes from the seed coat [10]. Germination sensu stricto starts with the uptake of water by the quiescent dry seed and terminates with the protrusion of the radicle and the elongation of the embryonic axis [10]
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