Calcium requirement of phytochrome-mediated fern-spore germination: No direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain

Abstract

Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca2+ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10(-4) M. At concentrations > or = 10(-1) M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La3+, an antagonist of Ca2+. From these results it is concluded that Ca2+ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca2+ the R-stimulated system remained capable of responding to Ca2+, added as late as 40 h after R. Moreover, Ca2+ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. "Coupling" of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting "escape kinetics" were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of phytochrome.

The Role(s) of Calcium Ions in Phytochrome Action

“…Spores irradiated with R reached 50% escape from reversi-bility after 22 h incubation (Diirr and Scheuerlein, 1990). Red light-induced Ca2+-dependent Dryopteris germination was significantly reduced by addition of 10 p M or higher La3+ to the medium; germination was completely blocked at 10 mM La3+ (Scheuerlein et al, 1989). Dormant turions of Spirodela polyrhyza after a cold after-ripening period can be stimulated to germinate by activation of phytochrome (Appenroth et al, 1989).…”

“…All three of the above-mentioned calcium-channel blockers inhibited phytochrome-mediated movements of Cassia fasciculata leaflets (Roblin et al, 1989(Roblin et al, , 1990. Lanthanium ions inhibit the phytochrome-controlled germination of Onoclea sensibilis (Wayne and Hepler, 1984), Dryopteris paleacea fern spores (Scheuerlein et al, 1989) and Spirodela polyrha turions .…”

“…The effect of phytochrome and Ca2+ on germination of Dryopteris paleacea spores has been extensively studied by Scheuerlein and colleagues (Durr and Scheuerlein, 1990;Scheuerlein et al, 1988Scheuerlein et al, , 1989. In non-green Dryopteris spores the first visible evidence of germination is the appearance of chlorophyll synthesis.…”

“…Independent of the delay between a R pulse and a FR pulse to remove Pfr, only a negligible response to Ca2+ addition was observed . Interaction between phytochrome and Ca2+ observed during swelling of wheat protoplasts (Bossen et al, 1988), unrolling of barley leaf sections (Viner et al, 1988), and germination of Spirodela turions ) differed from that recorded for R-induced fern spore germination (Wayne and Hepler, 1984;Iino et al, 1989;Scheuerlein et al, 1989). Wayne and Hepler (1984) studied the relationship between phytochrome photoconversion and Ca2+ transport.…”

The survival and establishment potential of spores of Cyathea delgadii Sternb. in soils from Itirapina and Moji Guaçu (SP), Brazil

“…Viability of most pteridophyte spores was believed to be retained when stored in very dry and cold conditions (Dyer 1979, Scheuerlein et al 1989). In our laboratory, the spores of C. delgadii are usually stored (after being air dried) in the dark in closed bottles at 4°C as they lose their viability very rapidly when stored in dry conditions at 25°C (Marcondes-Ferreira & Felippe 1984).…”