Figure 1.

RNS application to maintain seed quality in aged seeds subjected to controlled deteriorated treatment (CDT) mitigates reduction of endogenous NO level. (A) A decrease in seed vigor during the aging process is induced by CDT. Seed aging is linked to ROS accumulation, due to impaired ROS generation and ROS scavenging by the antioxidant system, decreased GSH pool and GSH/GSSG ratio (Bailly et al., 2008; Ratajczak et al., 2019), disturbances in phytohormonal balance—decreased ethylene and ABA level (Sano et al., 2016) and down-regulation of the proteins involved in glycolysis, tricarboxylic acid (TCA) cycle, the electron transport chain (ETC) and oxidative phosphorylation (Xin et al., 2011). (B) The application of nitric oxide (NO) or NO donors before CDT activates protecting mechanisms that prevent the reduction of seed vigor. NO pre-treatment of the seeds subjected to CDT improves their quality by (i) increasing of GSH level and GSH/GSSG ration, (ii) up-regulation of the expression of genes encoding γ-glutamylcysteine synthetase (γGCS), glutathione synthetase (GS), glutathione S-transferase (GST), glutathione peroxidase (GPx), (iii) stimulation of methionine metabolism due to up-regulation of the transcription of the genes encoding S-adenosyl-L-methionine synthetase (SAMS) and 1-aminocyclopropane-1-carboxylic acid synthase (ACS) enzymes of ethylene biosynthetic pathway (He et al., 2018). (C) The application of NO or NO donors during CDT improves seed vigor by inducing processes that lead to the initiation of repair of oxidative damages, mainly in mitochondria. NO stimulates (i) activity of enzymatic antioxidant system in mitochondria: catalase (CAT), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) (ii) leading to decreased H₂O₂ content in aged seeds, (iii) improves also mitochondrial function in aged seeds by enrichment of some proteins of TCA cycle: succinate-CoA ligase (ADP-forming) subunit and fumarate hydratase (Mao et al., 2018).