Growth, membrane potential and endogenous ion currents of willow (Salix viminalis) roots are all affected by abscisic acid and spermine

Growth measurements of hormone-treated roots from willow cuttings were combined with electrophysiological recordings to study hormone-induced changes in membrane potential and in endogenous ion currents. The mean growth rate of roots was 10 ± 2 μm min -1 in regular nutrient solution. It increased to 13 ± 2 μm min -1 after application of spermine and decreased to 0.07 ± 0.01 μm min -1 after treatment with abscisic acid (ABA). Transient depolarizations were elicited in root cortex cells by spermine, while ABA caused a transient hyperpolarization. All changes in membrane potential were accompanied by transient responses of the endogenous current. These responses suggest that first anions, then cations leave the root during spermine-induced depolarizations. From the changes of the endogenous current an apparent efflux of anions (presumably Cl - ) and cations (presumably K + ) of 200 to 700 pmol cm -2 per depolarization was calculated. To further investigate a possible relation between endogenous ion currents, growth and the growth regulators ABA and spermine, long-lasting extracellular vibrating-probe measurements were performed. Control roots showed an inward current of about 1.5 μA cm -2 at the apical elongation zone and an outward current with a maximum density of 1.3 μA cm -2 at the central and basal elongation zone. The addition of ABA and spermine (final concentration 0.1 mM) to the bathing medium affected the endogenous current in opposite ways: ABA caused a reduction of inward and outward current, while spermine stimulated both. Since protons are a major component of the endogenous current, and sucrose can be taken up by root cells from the apoplast via symport with H + , a role of the endogenous current in growth regulation is indicated.

[1]  L. Mullins,et al.  Ion fluxes during the action potential in Chara , 1958, The Journal of physiology.

[2]  A. B. Hope,et al.  THE ACTION POTENTIAL IN CHARA , 1964 .

[3]  R. Malmberg,et al.  Do Polyamines Have Roles in Plant Development , 1989 .

[4]  L. Mullins,et al.  Efflux of Chloride Ions during the Action Potential of Nitella , 1962, Nature.

[5]  Tadeusz Zawadzki,et al.  Action Potentials in Lupinus angustifolius L. shoots , 1973 .

[6]  H. Dziubińska,et al.  Electrical activity of the liverwort Conocephalum conicum: The all-or-nothing law, strength-duration relation, refractory periods and intracellular potentials , 1983 .

[7]  Eric Davies,et al.  Action potentials as multifunctional signals in plants: a unifying hypothesis to explain apparently disparate wound responses , 1987 .

[8]  F. Heidekamp,et al.  Abscisic acid-induced membrane potential changes in barley aleurone protoplasts : a possible relevance for the regulation of rab gene expression , 1994 .

[9]  E. Davies,et al.  Characteristics of action potentials in Helianthus annuus , 1991 .

[10]  B. C. Jarvis,et al.  RNA and protein metabolism during adventitious root formation in stem cuttings of Phaseolus aureus , 1985 .

[11]  S. Grego,et al.  Spermidine inhibits K+ uptake without interfering with the basal activity of plasma membrane proton pump , 1990 .

[12]  K. Oda.  Recording of the potassium efflux during a single action potential in Chara corallina , 1975 .

[13]  A. Hetherington,et al.  Some current aspects of stomatal physiology. , 1990 .

[14]  M. Weisenseel,et al.  Growth, Gravitropism, and Endogenous Ion Currents of Cress Roots (Lepidium sativum L.) : Measurements Using a Novel Three-Dimensional Recording Probe. , 1992, Plant physiology.

[15]  A. Miller,et al.  Correlation between Root-Generated Ionic Currents, pH, Fusicoccin, Indoleacetic Acid, and Growth of the Primary Root of Zea mays. , 1989, Plant physiology.

[16]  L. Jaffe,et al.  Natural H Currents Traverse Growing Roots and Root Hairs of Barley (Hordeum vulgare L.). , 1979, Plant physiology.

[17]  T. Zawadzki.  Action Potentials in Lupinus angustifolius L. Shoots V. SPREAD OF EXCITATION IN THE STEM, LEAVES, AND ROOT , 1980 .

[18]  Jörg Fromm,et al.  Characteristics of Action Potentials in Willow (Salix viminalis L.) , 1993 .

[19]  T. Kauppila.  Polyamines enhance recovery after sciatic nerve trauma in the rat , 1992, Brain Research.

[20]  K. Trebacz,et al.  Cytoplasmic Ca2+, K+, Cl-, and NO3- Activities in the Liverwort Conocephalum conicum L. at Rest and during Action Potentials , 1994, Plant physiology.

[21]  Bih Scott,et al.  Bioelectric Fields of Bean Roots and their Relation to Salt Accumulation , 1962 .

[22]  J. Zeevaart.  Metabolism and physiology of abscisic acid , 1988 .

[23]  Jörg Fromm,et al.  Electric Signals Released from Roots of Willow (Salix viminalis L.) Change Transpiration and Photosynthesis , 1993 .