**1. Introduction**

After pollination (double fertilization), the typical diploid embryos are covered by the triploid endosperm and the diploid testa. The triploid endosperm consists of nutritive tissues and living cells, while the diploid testa includes seed coat, maternal tissue, and dead cells. Seeds are the vital component allowing embryo dispersion and its consequent development into mature plants [1]. The seeds of monocots and dicots differ in their structure and method of emergence [1, 2]. However, here we comprehensively focus on the signaling pattern of the reactive oxygen species (ROS) and its interaction during the germination and dormancy condition.

Although the dispersal of seeds is absolutely dependent on various cues such as vitality, genotype, hardness, moisture, air, temperature, light, and duration of seed storage, endosperm weakening is one of the key factors that determine the protrusion of radicle. The term "coatassociated dormancy" refers to the mechanical constraint that can impair germination, while "embryo dormancy" is characterized by the embryo failure to develop [1–3].

After imbibition, the weakening of endosperm is dependent on the gas exchange/respiration. Loosening of the endosperm was suggested to be influenced by the proper localization of ROS and its fine regulation by the antioxidant systems [4, 5]. The proper reduction/oxidation of the ROS (redox homeostasis) plays a key role in the transition from quiescence to active state [6]. Gibberellins (GAs) are involved in the promotion of the endosperm weakening and, on the other hand, abscisic acid (ABA) at least partly inhibits this process either directly or indirectly [2, 3, 7]. Induction/inhibition of the genes responsible for the endosperm weakening is controlled by the ROS-GA-ABA [7–11]. Substantially, cross-talk of other phytohormones, such as ethylene, brassinosteroids and auxins, with GA and ABA were reported to be inevitable for the seed development [12].

Although research in seed biology has reached significant advancements, apparent continuum still lies in the mechanisms underlying germination and dormancy, which needs to be disclosed. In this chapter, the heuristic network on cross-talk between the ROS and phytohor‐ mones involved in the release and/or induction of dormancy has been discussed.
