Fig. 1.

Signalling role of H₂O₂ in the seed germination process. During the process of germination, H₂O₂ triggers seed storage protein carbonylation (PCB) that induces the oxidative pentose phosphate pathway (oxPPP) which supplements NADPH to thioredoxin (TRX) for seed germination. Furthermore, it stimulates an increase in GAs and a decrease of abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) through mitogen-activated protein kinase (MAPK) (Lozano et al., 1996; Job et al., 2005; Oracz et al., 2007; Barba-Espin et al., 2010, 2011; Bahin et al., 2011; Diaz-Vivancos et al., 2013). Upon mobilization of reserves, seed germination takes place with resurgence of metabolism. For dormancy alleviation, the ABA content should be high to maintain the dormant state after fruit ripening and, in the non-dormant state, GAs could be high, leading to germination (Liu et al., 2010).