**1. Introduction**

Seed dormancy is defined as the inability of seeds to germinate under favorable conditions. The quiescent stage of seeds enables their survival during the adverse period for further seedling development. The high level of seed dormancy is considered as a negative trait due to germination retardation and reduction in the length of the growing season. On the other hand, low level of seed dormancy leads to preharvest sprouting (PHS) and yield loss. Thus, the varieties with medium value of seed dormancy are the most desirable [1–4]. Seed dor‐ mancy is considered as a quantitative trait under the control of the genetic and environmen‐ tal signals. The primary dormancy is induced during seed maturation, and its expression occurs mainly in freshly harvested seeds in order to prevent precocious seed germination. After‐ripening, which is dry seeds' storage at room temperature, can reduce primary seed dormancy [1]. The secondary dormancy can be induced in the presence of unfavorable con‐ ditions even in initially nondormant seeds [5–7]. Environmental conditions such as cold or heat temperature (stratification), light, nitrate (NO3−), and nitric oxide (NO) can break the dormancy stage [1, 3, 6, 8, 9]. The level of seed dormancy depends on the season of a year. Deep dormancy is associated with sensing slow seasonal changes in winter. Shallow dor‐ mancy senses rapid condition changes in summer [10].

Induction and release of seed dormancy is mainly under the control of abscisic acid (ABA) and gibberellic acid (GA). ABA promotes seed dormancy and germination inhibition. Action of ABA is counteracted by GA, which promotes seed germination at appropriate time. The balance between ABA and GA is regulated by environmental conditions (light, temperature) and endog‐ enous signals [4, 6, 7, 11]. Other phytohormones, such as auxin, brassinosteroids, and ethylene, modulate the interaction between ABA and GA in the regulation of seed dormancy [2, 4, 12].

Seed dormancy in cereals is established during seed development; however, the time of seed dormancy release can be different. Some varieties loose dormancy when the harvest maturity is reached. There are also varieties ready for germination after seed physiological maturity (fully developed, but not dried seeds). In cereals, such as barley (*Hordeum vulgare*), wheat (*Triticum aestivum*), and sorghum (*Sorghum bicolor*), the switch between physiological and har‐ vest maturity is related to ABA decrease [7].

Here, we discuss the genetic and molecular bases of seed dormancy entrance and breaking in Arabidopsis and monocot plants, considering the action of components belonging to ABA, GA, and other phytohormone pathways. Additionally, the influence of environmental cues on ABA‐ and GA‐related genes is described.
