Developmental Physiology Apparent Dark Decay of Phytochrome Pfr in Fern Spores

Abstract

AbstractGermination of spores of Dryopteris fllix‐mas has been induced by two pulses of saturating red light, separated by a dark period of about 8 to 24 h. By chosing different wavelengths, different Pfr/Ptot levels could be established. Thus, by a “null method” the second pulse could be used as a “test pulse”, determining the actual Pfr level remaining from the “start pulse”, and thus providing information about an apparent Pfr decay. It cannot be decided yet whether this apparent Pfr decay results from dark destruction or dark reversion.The apparent Pfr decay depends, as expected, on the temperature, being accelerated with increasing temperatures. Moreover, the later after sowing that the decay is tested, the faster it proceeds; a tentative interpretion is that newly synthesized Pr undergoes faster decay after phototransformation than that phytochrome pool present in the resting spores. A third factor that influences the apparent Pfr decay is the Pfr/Ptot level established by the first pulse (start pulse). The lower this level, the slower the decay kinetics. This could be due to phytochrome biosynthesis partly compensating for Pfr destruction, and the relative contribution of this biosynthesis to the total effect increases with lower Pfr levels. Spores of D. paleacea yield virtually the same results.Whatever the real basis of the observed Pfr decay, i.e. destruction, reversion, or a combination of these reactions with biosynthesis, it can be concluded that modification of this Pfr decay by various factors is the basis of the effect of those factors on light‐induced germination.