Plant seeds and fruits have evolved as the typical propagation and dispersal units of angiosperms (Linkies et al.
2010).
Seeds are very complex and diverse plant organs; they store nutrients and allow far-distance dispersal as well as persistence of a species in the local habitat.
A typical mature angiosperm seed consists of the embryo covered by the maternal seed coat (testa) and in most cases by a more or less abundant layer of endosperm tissue between the embryo and testa (Fig. 1).
The endosperm is a product of double fertilization and serves as a nutrient source for the embryo during seed development.
It may also serve as a nutrient source for the emerging embryo during germination and seedling establishment, but another important role of the endosperm in mature seeds is its involvement in the regulation of germination timing (see below).
Due to their structure, low water content and mechanisms such as dormancy and desiccation tolerance, orthodox seeds are able to survive for long periods and harsh environmental conditions.
These features enable the timing of seed germination to weather conditions that are favorable for germination and further seedling development.
It has therefore been concluded that the evolution of seeds was one of the major reasons for the rapid distribution diversification and dominance of seed plants, in particular angiosperms that evolved more than 130 million years ago
(Crane et al. 1995; Friedman 1998; Linkies et al. 2010; Wang et al. 2009).