Tansley Review - New Phytologist 186: 817-831 (2010)

The evolution of seeds

Ada Linkies, Kai Graeber, Charles A. Knight*, Gerhard Leubner-Metzger*

University of Freiburg, Faculty of Biology, Institute for Biology II, Botany / Plant Physiology, Schänzlestr. 1, D-79104 Freiburg, Germany, Web: 'The Seed Biology Place' http://www.seedbiology.de (A.L., K.G., G.L.-M.)
Biological Sciences Department, California Polytechnic State University, San Luis Obispo, 7 CA 93401, USA (C.A.K.)
*Corresponding authors: C.A.K., G.L.-M.

Received December 21, 2009; accepted February 23, 2010; published online April 12, 2010
DOI 10.1111/j.1469-8137.2010.03249.x

Figure 2 Linkies Tansley Review 2010

Figure 2. Gymnosperm and angiosperm megagametophyte fertilization and the evolutionary history of the angiosperm embryo sac and endosperm.
Best hypothesis (Friedman & Ryderson, 2009) for the early evolution of the angiosperm megagametophyte.
Megagametophyte structure, fertilization and seed development of gymnosperms and angiosperms. The first angiosperms may have produced four-nucleate, four-celled megagametophytes (one developmental module). Double fertilization of the uninucleate haploid central cell in Nymphaeales and Austrobailyales yields diploid endosperms (Nuphar/Schisandra-type). In the common ancestor of all angiosperms except Amborella, Nymphaeales and Austrobailyales, insertion of a nuclear migration event at the two-nucleate syncytial stage led to initiation of two developmental modules and formation of a seven-celled, eight-nucleate female gametophyte (Polygonum-type). Modular duplication also occured independently in the lineage to the Amborella-type embryo sac; in addition asynchronous cell division in the micropylar module yields a third synergid in the Amborella trichopoda endosperm (Friedman & Ryderson, 2009). In addition to endosperm, perisperm in basal angiosperm seeds is known for Hydataceae, Nymphaeaceae, Cabomaceae and Trimeniaceae.

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