GAMETOPHYTE DEVELOPMENT IN FERNS.

The fern gametophyte has interested plant biologists for the past century because its structure and development is simple and amenable to investigation. Past studies have described many aspects of its development, including germination of the spore, patterns of cell division and differentiation, photomorphogenic or light-regulated responses, sex determination and differentiation of gametangia, hormone and pheromone responses, and fertilization. Several genes that are predicted to regulate some of these processes have been recently cloned, making it possible to analyze how these processes are controlled at a molecular level. The emergence of the fern Ceratopteris richardii as a model organism for readily identifying and characterizing mutations that affect key developmental processes in gametophytes makes it a powerful tool for dissecting the molecular mechanisms underlying these processes. If advances in gene cloning techniques and transformation are forthcoming in Ceratopteris, it is likely that the study of developmental processes in ferns will significantly contribute to our understanding of plant development and evolution beyond that which can be learned solely from studying angiosperms.