Endosperm - nutritive tissue for embryo I. Endosperm as the result of double fertizlization in angiosperms (Angiospermeae)

A review is given on advances in endosperm research in angiosperms. Endosperm is a very important nutritive tissue for the developing embryo. In sexually reproducing angiosperms endosperm develops as a consequence of double fertilization when one of male gametes is introduced to the central cell of megagametophyte. Of the three types of endosperm: nuclear, cellular and helobial, the nuclear pattern of development is most common and occurs in plants of major economic importance, including the cereals. Recently research is focused on processes and mechanisms involved in endosperm development in species with the nuclear type of endosperm, including monocots (mainly cereals) and dicots (the model plant Arabidopsis thaliana). This model represents a highly conserved mode of nuclear endosperm differentiation with several stages: coenocytic, cellularization, differentiation, maturation and programmed death. In the differentiated endosperm four major cell types have been recognized: starchy endosperm, aleurone cells, transfer cells, and the cells of the embryo-surrounding region. The mechanisms involved in the first two stages of endosperm development are very conserved among all groups of angiosperms; they involve nuclear migration during coenocytic stage and cell wall formation by cytoplasmic phragmoplasts. Also specification of cell fates via positional signaling and genetic basis of endosperm differentiation are reported. Several other topics are presented, such as endosperm cytology, the nature and origin of endosperm dosage system, mutation fie in Arabidopsis that allows endosperm development without fertilization, and endosperm development in vitro after the fusion of an isolated sperm and isolated central cell