Planta

, Volume 174, Issue 1, pp 8–18

The action potential of Dionaea muscipula Ellis

  • Dieter Hodick
  • Andreas Sievers
Article

Abstract

The intention of this investigation was to acquire more concise information about the nature of the action potential of Dionaea muscipula Ellis and the different types of cells generating and conducting it. It is shown by microelectrode measurements that, besides the sensory cells, all the major tissues of the trap lobes are excitable, firing action potentials with pronounced after-hyperpolarizations. The action potentials are strictly dependent on Ca2+. Their peak depolarizations are shifted 25–27 mV in a positive direction after a tenfold increase in external Ca2+ concentration. Perfusions with 1 mM ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) or 1 mM LaCl3 completely inhibit excitability. Magnesium ions only slightly affect the peak depolarizations but considerably prolong action potentials. Sodium azide and 2,4-dinitrophenol also abolish excitation, probably by reducing the intracellular ATP concentration. Furthermore, it is tested whether the sensory cells can be distinguished from the other cells of the trap by their electrical behaviour. The resting potentials of sensory cells (-161±7 mV) and mesophyll cells (-155±8 mV) are of the same magnitude. Changes in external ion concentrations affect resting and action potentials in both cell types in a similar way. Additional freeze-fracture studies of both cell types reveal similar numbers and distributions of intramembrane particles on the fracture faces of the plasma membrane, which is most likely the mechanosensor. These findings stress the view that the high mechanosensitivity of the sensory hair results from its anatomy and not from a specialized perception mechanism. It is proposed that trap closure is triggered by a rise in the cytoplasmic concentration of Ca2+ or a Ca2+-activated regulatory complex, which must exceed a threshold concentration. Since the Ca2+ influx during a single action potential does not suffice to reach this threshold, at least two stimulations of the trap are necessary to elicit movement.

Key words

Action potential Dionaea Plasma membrane (freeze etching) Resting potential Sensory cell 

Abbreviations

DNP

2,4-dinitrophenol

EF

exoplasmic fracture face

EGTA

ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid

Em

membrane potential

Em,r

resting potential

PF

protoplasmic fracture face

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Dieter Hodick
    • 1
  • Andreas Sievers
    • 1
  1. 1.Botanisches Institut der Universität BonnBonn 1Federal Republic of Germany

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