Abstract
Electrical transmembrane potential differences and resistances in different tissues of intact root tips of Lepidium sativum L. were investigated in a humid atmosphere by conventional glass-microelectrode techniques with the reference electrode at the surface (apoplast) of the root. The resting potential (inside negative) in cells of the root cap rose from-80 mV in external cell layers (secretion cells) to approx.-140 mV in central cells (statocytes). Measurements of the electric input resistance within the apoplast of the root tip (calyptra, meristem and elongation zone) yielded a preference for longitudinal contact (resistance per length of tissue approx. 3.4 GOhm m-1) compared with transversal contact (approx. 14 GOhm m-1). Similarly, the symplastic coupling expressed as the characteristic length (L) where a signal is reduced to 1/c compared with the origin yielded L y =390 μm in the longitudinal (y) direction and L x =140 μm in the transversal (x) direction. Cable analytical treatment of the symplastic input resistances (approx. 10 MOhm) resulted in low membrane resistances in the y-direction at the ends of cells compared with the membrane resistances in the x-direction (approx. 0.2 Ohm m2) of the lateral membranes in the approximately cylindrical cells. This anisotropy is discussed in terms of model calculations. The resistivity of the symplast was calculated to be about 2.5 Ohm m. The input current-voltage relationship displayed a slight curvature with increasing slope for the more negative membrane potential typical of membranes with electrogenic pumps. Even after massive electrical stimulation in the range from-50 to-150mV carried out to trace current-voltage curves, electrical excitations (action potentials) were not detected in the cells investigated.
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Abbreviations
- el:
-
voltage recording electrodes
- R :
-
resistance
- V r :
-
resting potential
References
Bates, G.W., Goldsmith, M.H.M., Goldsmith, T.H. (1982) Separation of tonoplast and plasma membrane potential and resistance in cells of oat coleoptiles. J. Membr. Biol. 66, 15–23
Behrens, H.M., Gradmann, D., Sievers, A. (1985) Membrane-potential responses following gravistimulation in roots of Lepidium sativum L. Planta 163, 463–472
Behrens, H.M., Weisenseel, M.H., Sievers, A. (1982) Rapid changes in the pattern of electric current around the root tip of Lepidium sativum L. following gravistimulation. Plant Physiol. 70, 1079–1083
Cheeseman, J.M., Hanson, J.B. (1980) Characterization of two electrogenic systems in corn roots. In: Plant membrane transport. Current conceptual issues, pp. 409–410, Spanswick, R.M., Lucas, W.J., Dainty, J., eds. Elsevier/North-Holland Biomedical Press, Amsterdam New York Oxford
Cole, K.S. (1968) Membranes, ions and impulses. University of California Press, Berkeley Los Angeles
Etherton, B., Keifer, D.W., Spanswick, R.M. (1977) Comparison of three methods for measuring electrical resistances of plant cell membranes. Plant Physiol. 60, 684–688
Ginsburg, H., Ginzburg, B.Z. (1974) Radial water and solute flows in roots of Zea mays. IV. Electrical potential profiles across the root. J. Exp. Bot. 25, 28–35
Gradmann, D., Hansen, U.-P., Slayman, C.L. (1982) Reaction-kinetic analysis of current-voltage relationships for electrogenic pumps in Neurospora and Acetabularia. Curr. Top. Membr. Transp. 16, 257–276
Grahm, L. (1964) Measurements of geoelectric and auxin-induced potentials in coleoptiles with a refined vibrating electrode technique. Physiol. Plant. 17, 231–261
Hertz, C.H. (1971) Bioelectric phenomena in graviperception. In: Gravity and the organism, pp. 151–158, Gordon, S.A., Cohen, M.J., eds. University of Chicago Press, Chicago London
Iversen, T.-H., Pedersen, K., Larsen, P. (1968) Movement of amyloplasts in the root cap cells of geotropically sensitive roots. Physiol. Plant. 21, 811–819
Jack, J.J.b., Noble, D., Tsien, R.W. (1975) Electric current flow in excitable cells. Clarendon Press, Oxford
Juniper, B.E., Barlow, P.W. (1969) The distribution of plasmodesmata in the root tip of maize. Planta 89, 352–360
Overall, R.L., Gunning, B.E.S. (1982) Intercellular communication in Azolla roots II. Electrical coupling. Protoplasma 111, 151–160
Pilet, P.E. (1982) Abscisic acid, one of the endogenous growth inhibitors regulating root gravireaction. In: Plant growth substances 1982, pp. 529–536, Wareing, P.F., ed. Academic Press, London New York
Rona, J.-P., Pitman, M.G., Lüttge, U., Ball, E. (1980) Electrochemical data on compartmentation into cell wall, cytoplasm, and vacuole of leaf cells in the CAM genus Kalanchoe. J. Membr. Biol. 57, 25–35
Rubery, P.H. (1980) The mechanism of transmembrane auxin transport and its relation to the chemiosmotic hypothesis of the polar transport of auxin. In: Plant growth substances 1979, pp. 50–60, Skoog, F., ed. Springer, Berlin Heidelberg New York
Sievers, A., Hensel, W. (1982) The nature of graviperception. In: Plant growth substances 1982, pp. 497–506, Wareing, P. F., ed. Academic Press, London New York
Sievers, A., Volkmann, D. (1972) Verursacht differentieller Druck der Amyloplasten auf ein komplexes Endomembran-system die Geoperzeption in Wurzeln? Planta 102, 160–172
Sievers, A., Volkmann, D. (1977) Ultrastructure of gravity-perceiving cells in plant roots. Proc. R. Soc. London B. 199, 525–536
Slayman, C.L. (1965) Electrical properties of Neurospora crassa. Effects of external cations on the intercellular potential. J. Gen. Physiol. 49, 69–92
Spanswick, R.M. (1972) Electrical coupling between cells of higher plants: a direct demonstration of intracellular communication. Planta 102, 215–227
Tanada, T., Vinten-Johansen, C. (1980) Gravity induces fast electrical field change in soybean hypocotyls. Plant Cell Environ. 3, 127–130
Volkmann, D. (1974) Amyloplasten und Endomembranen: Das Geoperzeptionssystem der Primärwurzel. Protoplasma 79, 159–183
Volkmann, D., Sievers, A. (1979) Graviperception in multicellular organs. In: Encyclopedia of plant physiology, N.S., vol. 7: Physiology of movements, pp. 573–600, Haupt, W., Feinleib, M.E., eds. Springer, Berlin Heidelberg New York
Wilkins, M.B. (1979) Growth-control mechanisms in gravitropism. In: Encyclopedia of plant physiology, N.S., vol. 7: Physiology of movements, pp. 601–626, Haupt, W., Feinleib, M.E., eds. Springer, Berlin Heidelberg New York
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Behrens, H.M., Gradmann, D. Electrical properties of the vertically growing root tip of Lepidium sativum L.. Planta 163, 453–462 (1985). https://doi.org/10.1007/BF00392702
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DOI: https://doi.org/10.1007/BF00392702