Ascorbic acid priming restores the seed vigor by enhancing the mitochondrial AsA-GSH cycle and related gene expression in the aged oat seeds.

Abstract

Seed priming is an effective way to activate defense mechanisms before germination, enhancing seed vigor and stress resistance. Ascorbic acid (AsA) is an important signaling molecule that plays a crucial role in balancing cellular reactive oxygen species. However, whether AsA priming can enhance seed vigor in oat (Avena sativa) and the underlying mechanisms remain unclear. This study primed aged seeds (controlled deterioration at 45°C for 5 days) with 1.5 mM AsA for 24 h. Primed seeds were then sampled after 36 h of imbibition for seed assays. Significant increases in germination percentage, vigor index, shoot and root length, coupled with a significant reduction in mean germination time, demonstrated that AsA priming effectively restored seed vigor. Ultrastructural observations of mitochondria isolated from embryos presented that AsA priming repaired structural damage in aged seeds, with intact double membranes and clear internal cristae observed. Excessive H₂O₂ accumulation was discovered in mitochondria of aged seeds, while AsA priming reduced H₂O₂ levels by increasing the activities of CAT, GR, MDHAR and DHAR. AsA priming also increased antioxidant content, particularly DHA, contributing to reduced oxidative stress. Furthermore, transcriptomic analysis highlighted the upregulation of genes associated with antioxidant defense, including APX, CAT, DHAR and MDHAR, indicating enhanced repair and protection pathways in the mitochondrial AsA-GSH cycle. This suggests that AsA priming would increase the activity of antioxidant enzymes, the content of antioxidants, and expression of genes related to AsA-GSH cycle in aged oat seeds, which was conducive to repairing mitochondrial damage and enhancing seed vigor.