Figure 8.—

Model of signal transduction pathways and cross talk between embryo and endosperm. On the basis of genetic evidence, four different signaling pathways between the embryo and the endosperm are postulated: an immediate early signal originating from the fertilization of the egg cell and stimulating endosperm fate adoption of the central cell; an early signal from the endosperm that stimulates in a quantitative manner embryo development; a mid-to-early action of the endosperm that is required for embryo development beyond a globular stage; and finally, a late signal stemming from the embryo and responsible for seed survival. For further explanation, see text.