Variants of endosperm

 The formation of seeds is an essential step in the life cycle of flowering plants (angiosperms). Seeds permit plants to survive at unfavorable conditions in a quiescent stage. They also serve as dispersal units and allow plants to spread out and colonize new territories. In addition, seeds are often nutritional units that support the germinating seedling, facilitating rapid growth during this crucial life phase. Thus, the proper formation of seeds is decisive for the reproductive success of a plant.

Seeds are highly elaborated structures composed of different tissues that represent different genetic systems: The embryo makes up the next plant generation and its growth is supported by the surrounding endosperm tissue. Usually, both the embryo and the endosperm are products of the so-called double fertilization that is unique for flowering plants. However, these two fertilization products are not genetically equivalent: In the case of diploid plants, one of the two haploid male gametes fertilizes the haploid egg cell and generates a diploid embryo whereas the second gamete fuses with the usually homodiploid central cell, giving rise to a triploid endosperm (SITTE et al. 2002). Embryo and endosperm are enclosed by a seed coat comprising several integument layers, which are contributed by the mother plant. Thus, there is an apparent need for a temporal and spatial coordination of growth of these different tissues. 

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