Auxin carriers in Cucurbita vesicles (original) (raw)

Abstract

Carrier-mediated uptake of indole-3-acetic acid (IAA) by microsomal vesicles from Cucurbita pepo L. hypocotyls was strongly inhibited by 2,4-dichlorophenoxyacetic acid (2,4-D; i 50= 0.3 μM) but only weakly by 1-naphthylacetic acid (NAA). The fully ionised auxin indol-3-yl methanesulphonic acid also inhibited (i 50=3 μM). The same affinity ranking of these auxins for the uptake carrier, an electroimpelled auxin anion-H+ symport, is demonstrable in hypocotyl segments. The specificity of the auxin-anion eflux carrier was tested by the ability of different nonradioactive auxins to compete with [3H]IAA and reduce the stimulation of net radioactive uptake by N-1-naphthylphthalamic acid (NPA), a noncompetitive inhibitor of this carrier. By this criterion, NAA and IAA had comparable affinities, with 2,4-D interaction more weakly. Stimulation of [3H]IAA uptake by NAA, as a result of competition for the efflux carrier, could also be demonstrated when a suitable concentration of 2,4-D was used selectively to inhibit the uptake carrier. However, when [3H]NAA was used, no stimulation of its association with vesicles by NPA, 2,3,5-triiodobenzoic acid, or nonradioactive NAA was found. In hypocotyl segments, [3H]NAA net uptake was much less sensitive to NPA stimulation than was [14C]IAA uptake. The apparent contradictions concerning NAA could be explained by carrier-mediated auxin efflux making a smaller relative contribution to the overall transport of NAA than of IAA. The relationship between carrier specificity as manifested in vitro and the specificity of polar auxin transport is discussed.

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Abbreviations

2,4-D:

2,4-dichlorophenoxyacetic acid

IAA:

indole-3-acetic acid

ION3:

mixture of 4 μM carbonylcyanide _m_-chlorophenylhydrazone, nigericin and valinomycin

IMS:

indol-3-yl methanesulphonic acid

NAA:

1-naphthylacetic aci

NPA:

N-1-naphthylphthalamic acid

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Author notes

1. M. Sabater
   Present address: Departamento de Biología, Facultad de Biología, Universidad de Murcia, Espinardo, Murcia, Spain

Authors and Affiliations

1. Department of Biochemistry, University of Cambridge, CB2 1QW, Cambridge, UK
   M. Sabater & P. H. Rubery

Authors

1. M. Sabater
2. P. H. Rubery

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Sabater, M., Rubery, P.H. Auxin carriers in Cucurbita vesicles.Planta 171, 514–518 (1987). https://doi.org/10.1007/BF00392300

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• Received: 24 April 1987
• Issue date: August 1987
• DOI: https://doi.org/10.1007/BF00392300

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