Developmental Biology of Fern Gametophytes

Homosporous ferns produce an immense quantity of spores. Fern spores are relatively resistant to extremes of environmental conditions and persist in a viable, yet metabolically inactive state for long periods of time. Although no one can explain all that is going on in the spore during this period of enforced rest, the hiatus may well be valuable to the spore to plot a survival strategy and form the gametophyte when conditions are most propitious. While the spore is the first cell of the gametophytic phase, development of the gametophyte itself begins with the germination of the spore. It is therefore appropriate that attention is paid to the various factors that keep spores alive for prolonged periods and potentiate their germination. Accordingly, the present chapter is concerned with the physiological aspects of viability, dormancy, and germination of spores; the morphogenetic, metabolic, and biochemical changes during germination are treated in the next two chapters. Understanding of the physiological mechanisms of dormancy and germination of fern spores has benefited immeasurably in recent years from developments in the field of seed germination. However, references will be made in this chapter to the inescapable parallels that exist between seed germination and spore germination only when it is considered necessary to explain certain concepts further.