Embryogenic plant cells in microgravity.

Plant development entails an orderly progression of cellular events both in terms of time and geometry. There is circumstantial evidence that in the controlled environment of the higher plant embryo sac gravity (g) may play a role in shaping embryo development. It follows that normal embryo development may not occur reliably and efficiently under the weak microgravity environment of space. More attention must be given to studying the many aspects of reproductive biology in the space environment in order to be confident that higher plants will not only survive, but produce large numbers of viable embryos in a "seed to seed to seed" type experiment. Until the time arrives when successive generations of flowering plants can routinely be grown and intensively studied, the best we can do is to utilize acceptable surrogate systems and begin, piece-meal, to accumulate information on important aspects of plant reproduction in microgravity. Cultured cells can play an important role in these activities since they can be grown to be morphogenetically competent and can be evaluated as to their ability to simulate embryogenic events usually identified with fertilized eggs in the embryo sac of the ovule in the ovary. Cultured cells can also be manipulated with relative ease. The extreme plasticity of such demonstrably totipotent cell systems provides a means to test environmental effects such as microgravity on a potentially "free-running" entity without the constraints or confines of an embryo sac. The successful manipulation and management of plant cells and propagules in space also has significance for exploitation of biotechnologies in microgravity since embryogenic systems, perforce, are an important component of plant genetic engineering manipulations.