title: Initial events in the tip-swelling response of the filamentous gametophyte of Onoclea sensibilis L. to blue light.
abstract: Several inhibitors were applied to filamentous gametophytes of the fern Onoclea sensibilis in the attempt to characterize how electrical phenomena might be involved in the tip-swelling response to blue light (BL). The membrane potential of the apical cell in the typical fern filament rests near-120 mV in darkness, but irradiation with blue light causes the membrane to hyperpolarize at a steady rate of 2.6 mV min(-1) until it reaches a new stable value between-130 and-135 mV. In darkness, 10(-4)M salicylhydroxamic acid (SHAM), an inhibitor of BL-mediated absorbance changes in putative plasma-membrane fractions from maize coleoptiles, has no observable effects on the membrane potential or on filamentous growth. A SHAM pretreatment before BL irradiation causes approx. 70% inhibition of the membrane hyperpolarization as well as a comparable reduction in the growth response; however, SHAM has no effect in experiments where its application follows the onset of the electrical response. Exposing the filaments to 10(-5)M Na3VO4, an inhibitor of the plasma-membrane ATPase, depresses the membrane potential in darkness. Depending on the timing of application, Na3VO4 prevents the initiation of or blocks further increases in the BL-mediated hyperpolarization. Application of Na3VO4 causes an immediate cessation of growth in both darkness and BL. These findings implicate the involvement of a plasmalemma-bound flavin-cytochrome complex and ATP-driven proton pump in the initial events of this growth response to blue light.
authors.affiliation: Department of Botany, University of Maryland, 20742, College Park, MD, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Cooke
authors.forename: R H
authors.initials: RH
authors.lastname: Racusen
authors.forename: W R
authors.initials: WR
authors.lastname: Briggs