Embryogenesis

Summary

Introduction

In higher plants, fertilization of the ovule leads to the formation of the embryo. Zygotic embryogenesis, the way in which the fertilized ovule develops, has been studied extensively; changes that occur have been described for many plant species at the level of morphology, metabolism, protein composition, and gene expression. Interestingly, plant embryos can also develop in the absence of a fertilized ovule, from somatic cells in callus culture (Sung et al., 1984), from differentiated cells such as leaf mesophyll (Conger et al., 1983) and, perhaps most surprisingly, from immature haploid male gametes termed microspores (Nitsch, 1969; Dunwell, 1985). These alternative routes to the formation of an embryo illustrate both the means by which plants use environmental stimuli as developmental signals and the plasticity of plant development that is maintained throughout growth.

This article is not a comprehensive review of embryogenesis but rather a brief introduction to some interesting key issues in the area, and an outline of the ways in which we have been approaching the subject at Leeds. Two principal issues about plant embryogenesis will be discussed. The first concerns embryo formation, and the second concerns the way in which an embryo, fully capable of germinating within days of organ primordia differentiation, is nevertheless prevented from doing so until seed development has been completed.