Early Morphogenetic Changes During Phytochrome-induced Fern Spore Germination I. The Existence of a Pre-photoinduction Phase and the Accumulation of Chlorophyll

Abstract

The relationship between light induced and dark metabolic processes occurring during synchronous germination of unicellular spores of the fern Pteris vittata was investigated. Light was almost totally ineffective as an inducer during a 12 to 16 h preinduction phase. Spores imbibed in the cold before illumination could not be induced to germinate, indicating that metabolic events occurring during the preinduction phase are required for the photomorphogenetic response. Two brief irradiations separated by two hours of darkness during a later, photoinductive phase were more effective in inducing germination than a single one of equal fluence. These short red-light illuminations induced more than 40% synchronous germination and enabled the separation between hydration and light effects. Chlorophyll formation is a phytochrome induced dark process in germinating spores, preceding the first nuclear division and rhizoid emergence. The formation of chlorophyll in ferns in the dark differs from light mediated chlorophyll synthesis in both angiosperms and gymnosperms as it is an enzymatic process, yet is mediated by phytochrome photoconversion.