Apospory and Apogamy: Implications for Understanding the Plant Life Cycle

Abstract

Although apospory and apogamy are commonly regarded as aberrations, it is conceivable that they were frequent phenomena in ancient floras. In living plants apospory and apogamy offer the opportunity to investigate the factors causing change of reproductive phase in situations uncomplicated bysporogenesis or by gametogenesis and fertilization. Work with homosporous plants indicates that stress, either in the form of nutritional deprivation or conversely enhancement, particularly in the form of respirable substrate, is effective in switching gene activation from sporophytic to gametophytic and vice versa. In the bryophytes, notably the mosses, both phases can often be made unstable equally readily in appropriate experimental conditions. In vascular homosporous plants the change from sporophyte to gametophyte is usually more easily induced than the converse. The same conceptual approach can be applied to the heterosporous plants, but here the sporophytic condition seems more stable than the gametophytic. In ...