Embryo and endosperm function and failure in Solanum species and hybrids

Abstract

Although the importance of the endosperm as a food store in many angiosperm seeds is well known, its significance during early embryogenesis has been neglected. In many interspecific hybrids, and in some other situations, embryos do not develop fully and abort. It has often been stated that this is caused by the endosperm failing to conduct sufficient nutrients to the embryo, but seldom has it been suggested that the endosperm actively controls most of the early stages of morphogenesis of the embryo. Information gleaned from a broad survey of the literature, combined with additional evidence presented here, obtained from Solanum incanum and interspecific hybrids, indicate that the endosperm is dynamic and very active in regulating early embryo development. This requires highly integrated genetic control of rapidly changing metabolism in the endosperm. In interspecific hybrids, lack of coordination may cause unbalanced production of growth regulating substances by the endosperm and hence abortion of the embryo, or even unregulated production of nucleases and proteases resulting firstly in autolysis of the endosperm and then digestion of the embryo. The endosperm may thus serve to detect inappropriate hybridization of species or ploidy levels and so prevent waste of resources by producing seeds that would result in sterile hybrids or unthrifty subsequent generations. This discriminatory function of the endosperm has diminished during evolution and domestication of the crop plant Solanum melongena L.