title: 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.
authors.affiliation: Department of Botany, University of Texas, Austin 78713.
authors.forename: R
authors.initials: R
authors.lastname: Scheuerlein
authors.forename: R
authors.initials: R
authors.lastname: Wayne
authors.forename: S J
authors.initials: SJ
authors.lastname: Roux
mesh_terms: D002118:Calcium / Q000037:antagonists & inhibitors / Q000502:physiology*; D003470:Culture Media; D018525:Germination / Q000502:physiology* / Q000528:radiation effects; D007811:Lanthanum / Q000494:pharmacology; D008027:Light; D017440:Photoperiod; D010834:Phytochrome / Q000378:metabolism*; D018521:Plant Physiological Phenomena; D010944:Plants / Q000187:drug effects / Q000528:radiation effects; D015398:Signal Transduction / Q000502:physiology*; D013170:Spores / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D013997:Time Factors
chemical_list: D003470:Culture Media; D010834:Phytochrome; D007811:Lanthanum; D002118:Calcium