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Planta

, Volume 163, Issue 4, pp 463–472 | Cite as

Membrane-potential responses following gravistimulation in roots of Lepidium sativum L.

  • H. M. Behrens
  • D. Gradmann
  • A. Sievers
Article

Abstract

Membrane potentials were measured in lateral statocytes of vertically and nonvertically growing roots of Lepidium sativum L. using conventional glass-microelectrode techniques. Statocytes in vertically growing roots showed a stable resting potential of-118±5.9 mV without spontaneous fluctuations. Upon tilting the root 45° from the vertical, an electrical asymmetry was observed. Statocytes on the physically lower side of the root depolarized by approx. 25 mV. This depolarization occurred following a latent period of 8 s reaching a minimum (approx.-93 mV) after 170 s. This depolarization is the earliest event in graviperception ever recorded. After this depolarization, the cell repolarized within 60 s to a potential approx. 10 mV more positive than the original resting potential. Statocytes on the upper flank showed a slow hyperpolarization (t1/2h=half time for hyperpolarization=168 s) reaching a final, stable potential at a level 10 mV more negative. These effects of gravistimulation were statenchyma-specific, since cells in the cortex and rhizodermis showed no similar effects. The gravi-electrical responses were observed in 25% of all roots tested. Roots which showed no gravi-electrical response had a reduced elongation growth, lacked gravity-induced bending and lacked the typical structural polarity in punctured statocytes. This observed transition from a symmetrical pattern of resting potential in the statenchyma to an asymmetrical pattern following gravistimulation supports the results observed with external current measurements (Behrens et al., Plant Physiol. 70, 1079–1083, 1982) and extends these results to the cellular level and to considerably improved temporal resolution. The asymmetry in the gravi-electrical response extends the graviperception model of Sievers and Volkmann (Planta 102, 160–172, 1972) which comprises an asymmetrical sedimentation of the amyloplasts on the distal endoplasmic reticulum of statocytes. This generates an intraorgan signal which then must be transmitted to the growth zone.

Key words

Electrical current (graviperception) Gravielectrical response Graviperception Intracellular potential Lepidium Root tip (graviperception) Statocyte 

Abbreviation

ER

endoplasmic reticulum

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Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • H. M. Behrens
    • 1
  • D. Gradmann
    • 2
  • A. Sievers
    • 1
  1. 1.Botanisches Institut der UniversitätBonn
  2. 2.Pflanzenphysiologisches Institut der UniversitätGöttingenFederal Republic of Germany

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