Seed birth to death: dual functions of reactive oxygen species in seed physiology

Abstract

Background: Reactive oxygen species (ROS) are considered to be detrimental to seed viability. However, recent studies have demonstrated that ROS have key roles in seed germination particularly in the release of seed dormancy and embryogenesis, as well as in protection from pathogens.

Scope: This review considers the functions of ROS in seed physiology. ROS are present in all cells and at all phases of the seed life cycle. ROS accumulation is important in breaking seed dormancy, and stimulating seed germination and protection from pathogens. However, excessive ROS accumulation can be detrimental. Therefore, knowledge of the mechanisms by which ROS influence seed physiology will provide insights that may not only allow the development of seed quality markers but also help us understand how dormancy can be broken in several recalcitrant species.

Conclusions: Reactive oxygen species have a dual role in seed physiology. Understanding the relative importance of beneficial and detrimental effects of ROS provides great scope for the improvement and maintenance of seed vigour and quality, factors that may ultimately increase crop yields.

Keywords: Reactive oxygen species (ROS); embryogenesis; germination; programmed cell death (PCD); seed dormancy; seed physiology; signalling.

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).