An Embryogenic Culture of Soybean: Towards a General Theory of Somatic Embryogenesis

Abstract

It is a simple matter of definition to say that an embryogenic cell culture is composed of embryogenic cells, and quite another matter to understand why certain cells are embryogenic or have embryogenic potential. We know “what” they are, of course: they are cells which will make somatic embryoids in response to an appropriate stimulus, typically the removal of the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D) from the culture medium. In many cases, this knowledge may be enough. Practical applications do not require that we know “why” they make embryos, but only that we can recognize such embryogenic cells and can obtain or produce cultures containing large numbers of such cells or cell masses. Certainly, somatic embryogenesis has been described in a large number of species, including species of major and minor agronomic importance (1), even down to the last recalcitrant ones, cotton (9) and soybeans (7). But this is not somatic embryogenesis with ease, and not in every cultivar, and not from any tissue source of any physiological state or age. This is, I believe, a direct consequence of our lack of understanding about the “whys” of embryogenic competence even though we understand the “whats” and the “hows.” Previous papers in this volume describe the importance of preconditioning the plant or explant.