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

✍ Scribed by R. Scheuerlein; R. Wayne; S. J. Roux

• Publisher: Springer-Verlag
• Year: 1989
• Tongue: English
• Weight: 563 KB
• Volume: 178
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00392523

✦ Synopsis

Phytochrome-mediated germination of fern spores ofDryopterispaleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h ofimbibition. For its realization external Ca 2 + was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10 -4 M. At concentrations > 10-1M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La 3 +, an antagonist of Ca 2+. From these results it is concluded that Ca 2 + influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca 2 + the R-stimulated system remained capable of responding to Ca 2+, added as late as 40 h after R. Moreover, Ca 2 + 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 * A preliminary report of this work was presented at the XIV Int. Bot. Congr., Berlin (West), Germany, Book of Abstracts, 2-116a-5 (1987)