Spermidine-Driven DNA Damage Response and Metabolome Dynamics at the Cross-Road Between Germination and Seedling Development in Medicago truncatula

High-quality seeds resulting from priming treatments show fast deterioration under storage. Such a drawback could be overcome using antioxidant compounds as priming agents. In this study, spermidine-treated and hydroprimed Medicago truncatula seeds were subjected to controlled deterioration. To disclose the impact of spermidine on genome maintenance, crucial for successful seed germination, DNA damage was evaluated using comet assay whereas DDR (DNA damage response) and cell cycle gene expression were monitored by qRT-PCR. DNA damage levels were decreased only in spermidine-treated imbibed seeds and seeds collected at the radicle protrusion stage, concomitant with enhanced accumulation of DDR gene transcripts. The mitigating effects of spermidine disappeared during seedling development, leading to increased occurrence of aberrant phenotypes. Non-targeted metabolomics was applied to M. truncatula seeds and seedlings to identify those metabolites associated with the enhanced repair response occurring during germination as well as with the poor repair activity of developing seedlings. Spermidine-mediated accumulation of γ-aminobutyric acid (GABA), ascorbic acid, dehydroascorbic acid, xanthine and allantoin was observed at the radicle protrusion stage.