Abstract
Ethylene is an important component of the gaseous environment, and regulates numerous plant developmental processes including seed germination and seedling establishment. Dormancy, the inability to germinate in apparently favorable conditions, has been demonstrated to be regulated by the hormonal balance between abscisic acid (ABA) and gibberellins (GAs). Ethylene plays a key role in dormancy release in numerous species, the effective concentrations allowing the germination of dormant seeds ranging between 0.1 and 200 μL L-1. Studies using inhibitors of ethylene biosynthesis or of ethylene action and analysis of mutant lines altered in genes involved in the ethylene signaling pathway (etr1, ein2, ain1, etr1, and erf1) demonstrate the involvement of ethylene in the regulation of germination and dormancy. Ethylene counteracts ABA effects through a regulation of ABA metabolism and signaling pathways. Moreover, ethylene insensitive mutants in Arabidopsis are more sensitive to ABA and the seeds are more dormant. Numerous data also show an interaction between ABA, GAs and ethylene metabolism and signaling pathways. It has been increasingly demonstrated that reactive oxygen species (ROS) may play a significant role in the regulation of seed germination interacting with hormonal signaling pathways. In the present review the responsiveness of seeds to ethylene will be described, and the key role of ethylene in the regulation of seed dormancy via a crosstalk between hormones and other signals will be discussed.
Highlights
In soil, seeds are exposed to various environmental factors including temperature, moisture, oxygen and light, which regulate seed germination, and subsequent seedling growth
We describe how ethylene interacts with other plant hormones in regulation of germination and dormancy, concentrating on its interactions with abscisic acid (ABA), GAs, and reactive oxygen species (ROS)
In pea, which germination is not strongly regulated by ethylene, Barba-Espin et al (2011) demonstrate that H2O2 treatment results in a reduction in PsACS2 transcript abundance consistent with a decrease in ACC content. These results suggest that ROS and ethylene probably do not interact directly, but rather through a complex hormonal network (Diaz-Vivancos et al, 2013)
Summary
Seeds are exposed to various environmental factors including temperature, moisture, oxygen and light, which regulate seed germination, and subsequent seedling growth. SEED RESPONSIVENESS TO EXOGENOUS ETHYLENE Exogenous ethylene or ethephon, an ethylene releasing compound, improves germination in numerous species (Esashi, 1991; Corbineau and Côme, 1995; Kepczynski and Kepczynska, 1997; Matilla, 2000; Matilla and Matilla-Vazquez, 2008; Arc et al, 2013) It stimulates germination of non-dormant seeds incubated in non-optimal environmental conditions such as too high temperatures (Rao et al, 1975; Abeles, 1986; Gallardo et al, 1991), osmotic stress (Negm and Smith, 1978; Kepczynski, 1986; Khan et al, 2009), hypoxia (Esashi et al, 1989; Corbineau and Côme, 1992), and salinity (Zapata et al, 2003; Wang et al, 2011; Lin et al, 2013; Silva et al, 2014). Breaking of dormancy either during chilling in apple (Sinska, 1989) or dry storage in sunflower (Corbineau and Côme, 2003), Amaranthus retroflexus (Kepczynski and Sznigir, 2014) and Stylosanthes www.frontiersin.org
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