Planta

, Volume 118, Issue 2, pp 101–121 | Cite as

Carrier-mediated auxin transport

  • P. H. Rubery
  • A. R. Sheldrake
Article

Summary

  1. 1.

    Auxin (IAA) transport was investigated using crown gall suspension tissue culture cells. We have shown that auxin can cross the plasmalemma both by transport of IAA anions on a saturable carrier and by passive (not carriermediated) diffusion of the lipid-soluble undissociated IAA molecules (pK=4.7). The pH optimum of the carrier for auxin influx is about pH 6 and it is half-saturated by auxin concentrations in the region of 1–5 μM. We found that the synthetic auxin 2,4D specifically inhibited carrier-mediated IAA anion influx, and possibly also efflux. Other lipid-soluble weak acids which are not auxins, such as 3,4-dichlorobenzoic acid, had no effect on auxin transport. By contrast, we found that TIBA, an inhibitor of polar auxin transport in intact tissues inhibited only the carrier-mediated efflux of IAA.

     
  2. 2.

    When the pH outside the cells is maintained below that of the cytoplasm (pH 7), auxin can be accumulated by the cells: In the initial phase of uptake, the direction of the auxin concentration gradient allows both passive carrier-mediated anion influx (inhibited by 2,4D) and a passive diffusion of undissociated acid molecules into the cells. Once inside the cytoplasm, the undissociated molecules ionise, producing IAA anions, to a greater extent than in the more acidic extracellular environment. Uptake by passive diffusion continues as long as the extracellular concentration of undissociated acid remains higher than its intra-cellular concentration. Thus, the direction of the auxin anion concentration gradient is reversed after a short period of uptake and auxin accumulates within the cells. The carrier is now able to mediate passive IAA anion efflux (inhibited by TIBA) down this concentration gradient even though net uptake still proceeds because the carrier is saturable whereas passive diffusion is not.

     
  3. 3.

    Auxin “secretion” from cells is regarded as a critical step in polar auxin transport. The evidence which we present is consistent with the view that auxin “secretion” depends on a passive carrier-mediated efflux of auxin anions which accumulate within the cells when the extra-cellular pH is below that of the cytoplasm. The implications of this view for theories of polar auxin transport are discussed.

     

Abbreviations

IAA

indol-3-yl acetic acid

2,4D

dichlorophenoxyacetic acid

TIBA

2,3,5-tri-iodobenzoic acid

PIPES

piperazine-NN′-bis-2-ethane sulphonic acid

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Caldwell, P. C.: Intracellular pH. Int. Rev. Cytol. 5, 229–227 (1956)Google Scholar
  2. Cande, W. Z., Goldsmith, M. H. M., Ray, P. M.: Polar auxin transport and auxin-induced elongation in the absence of cytoplasmic streaming. Planta (Berl.) 111, 297–314 (1973)Google Scholar
  3. Christie, A. E., Leopold, A. C.: On the manner of triiodobenzoic acid inhibition of auxin transport. Plant & Cell Physiol. 6, 337–345 (1965)Google Scholar
  4. Fawcett, C. H., Wain, R. L., Wightman, F.: Plant growth-regulating activity in certain carboxylic acids not possessing a ring structure. Nature (Lond.) 178, 972–974 (1956)Google Scholar
  5. Goldsmith, M. H. M.: Transport of plant growth regulators. In: The physiology of plant growth and development, pp. 127–162, Wilkins, M. B., ed. London: McGraw-Hill 1969Google Scholar
  6. Goldsmith, M. H. M., Ray, P. M.: Intracellular localisation of the active process in polar transport of auxin. Planta (Berl.) 111, 297–314 (1973)Google Scholar
  7. Hertel, R., Evans, M. L., Leopold, A. C., Sell, H. M.: The specificity of the auxin transport system. Planta (Berl.) 85, 238–249 (1969)Google Scholar
  8. Hertel, R., Flory, R.: Auxin movement in corn coleoptiles. Planta (Berl.) 82, 123–144 (1968)Google Scholar
  9. Hertel, R., Leopold, A. C.: Versuche zur Analyse des Auxinstransports in der Koleoptile von Zea mays L. Planta (Berl.) 59, 535–562 (1963)Google Scholar
  10. Hertel, R., Thomson, K.-St., Russo, V. E. A.: In-vitro auxin binding to particulate cell fractions from corn coleoptiles. Planta (Berl.) 107, 325–340 (1972)Google Scholar
  11. Jones, R. L., Metcalfe, T. P., Sexton, W. A.: The relationship between the constitution and the effect of chemical compounds on plant growth. 3. Chlorinated benzaldehydes and benzoic acids. Biochem. J. 48, 422–425 (1951)Google Scholar
  12. Jönsson, Å.: Chemical structure and growth activity of auxins and antiauxins. In: Encyclopedia of Plant Physiology, vol. XIV, pp. 959–1006, Ruhland, W., ed. Berlin-Heidelberg-New York: Springer 1961Google Scholar
  13. Rayle, D. L.: Auxin-induced hydrogen ion secretion in Avena coleoptiles and its implications. Planta (Berl.) 114, 63–73 (1973)Google Scholar
  14. Rubery, P. H.: Studies on indoleacetic acid oxidation by liquid medium from crown gall tissue culture cells: The role of malic acid and related compounds. Biochim. biophys. Acta (Amst.) 261, 21–34 (1972)Google Scholar
  15. Rubery, P. H., Sheldrake, A. R.: Effect of pH and surface charge on cell uptake of auxin. Nature (Lond.) New Biol. 244, 285–288 (1973)Google Scholar
  16. Sabnis, D. D., Audus, L. J.: Growth substances interactions during uptake by mesocotyl sections of Zea mays L. Ann. Bot. 31, 263–281 (1967)Google Scholar
  17. Sheldrake, A. R.: The polarity of auxin transport in inverted cuttings. New Phytologist 73, 639–644 (1974)Google Scholar
  18. Thomson, K.-S., Leopold, A. C.: In-vitro binding of morphactins and 1-N-naphthylphthalamic acid in corn coleoptiles and their effects on auxin transport. Planta (Berl.) 115, 259–270 (1974)Google Scholar
  19. Thomson, K.-S., Hertel, R., Müller, S.: 1-N-Naphthylphthalamic acid and 2,3,5-triiodobenzoic acid. In-vitro binding to particulate cell fractions and action on auxin transport in corn coleoptiles. Planta (Berl.) 109, 337–352 (1973)Google Scholar
  20. Zimmerman, P. W., Hitchcock, A. E., Prill, E. A.: Substituted benzoic acids as growth regulators. Contr. Boyce Thompson Inst. 16, 419, 427 (1952)Google Scholar

Copyright information

© Springer-Verlag 1974

Authors and Affiliations

  • P. H. Rubery
    • 1
  • A. R. Sheldrake
    • 1
  1. 1.Department of BiochemistryCambridgeUK
  2. 2.The International Crop Research Institute for the Semi-Arid TropicsHyderabadIndia

Personalised recommendations