Sequential Photoregulation of Fern-Spore Germination

Abstract

Summary Spores of Dryopteris filix-mas have an absolute light requirement for germination, which is mediated by phytochrome. The effect of a single red pulse 24 h after sowing is potentiated by a light pretreatment, given before the spores acquire competence to P fr . This pretreatment (the inducing effect of which is abolished by a far-red pulse) can consist of a single pulse as well; P fr has to be present for several hours, and is most effective towards the end of the pretreatment period. The effect does not require the maximum possible P fr level, and even a level of 10–20% P fr /P tot can significantly enhance the result of the subsequent inducing pulse. Generally, the pretreatment effect is greatest, if the inducing pulse is given with a non-saturating fluence or with a wavelength establishing an intermediate P fr level. It is assumed, and will be tested in future experiments, that P fr resulting from both pretreatment and inducing pulses act upon the same system, and that their products add to each other to surpass a threshold allowing germination.