Phytochrome-Mediated Fern-spore Germination: A Temperature-Sensitive Phase in the Transduction Chain after the Action of P fr

Abstract

Summary Phytochrome-mediated spore germination in Dryopteris filix-mas is inhibited if the temperature is raised from 22 to 32°C. So far, the sensitivity to that temperature effect was found for a period before the red-light pulse and during the coupling phase, i.e. before and during the active form of phytochrome, P fr , initiates the transduction chain. The present paper shows that the effect extends into the first 4–5 h after far-red, i.e., «postcoupling processes» are affected that are no longer controlled by P fr . This effect is obtained after a non-saturating period of P fr action, whereas it disappears after a saturating period, when almost all spores have completed coupling and have started the postcoupling processes already before the far-red pulse. This dependence on the experimental conditions demonstrates the importance of careful consideration of the great variation: The duration of the coupling process ranges from a few hours to about one day in a population; thus, the latter always comprises a mixture of several phases or subphases. In combination with earlier reports on effects of nitrate and calcium, the results allow for an improved characterization of the early postcoupling phase. A first subphase of 4–5 h duration is characterized by its sensitivity to elevated temperatures (as well as to nitrate deficiency, Haas and Scheuerlein, 1991 ); it is followed by a subphase that is insensitive to temperature and nitrate. Fifteen hours later, a short period of calcium requirement ( Durr and Scheuerlein, 1990 ) terminates this second subphase.