Interactions between auxin efflux carriers and NPA receptors in higher plant cells
Interactions between auxin efflux carriers and NPA receptors in higher plant cells
Phytotropins such as N-1-naphthylphthalamic acid (NPA) are potent non-competitive inhibitors of the efflux of indole-3-acetic acid (IAA) from higher plant cells, and of polar auxin transport. Little is known about mechanisms by which components of the efflux carrier/NPA receptor complex are targeted to, or turned over in the plant cell plasma membrane. Intracellular protein targeting (monensin) and translation (cycloheximide - CH) inhibitors were used to probe this system.
Monensin stimulated the net uptake of [1-14C]IAA by small segments of light-grown pea internode (Pisum sativum L.) or dark-grown zucchini hypocotyl (Cucurbita pepo L.) after a time lag of 20 minutes. It eliminated the typical biphasic response of [1-14C]IAA net uptake to increasing concentrations of competing unlabelled IAA, it inhibited polar IAA transport in long stem segments, and it inhibited the efflux of [1-14C]IAA from preloaded tissue segments within 20 minutes. Uptake carrier activity was not reduced by 10-6 (pea) or 10-7 (zucchini) mol.dm-3 monensin. Higher monensin concentrations, and pretreatment of tissue segments with 10-5 mol.dm-3 CH for at least 1h, reduced the response of [1-14C]IAA net uptake to NPA at pH 5.0, but had no effect on uptake in the absence of NPA. However reducing the pHext rescued 3x10-5 mol.dm-3 monensin- and CH-induced stimulations of IAA net uptake. Both compounds inhibited the efflux of IAA from preloaded tissue segments, but stimulatory effects of reduced efflux on net uptake are proposed to be masked by concomitant inhibitory effects of monensin and CH on other components of IAA net uptake, which contribute more to this when the pHext is greater than 5.0. Neither monensin nor CH affected the net uptake of the ΔpH probe [2-^14C]5,5-dimethyl-oxazolidine-2,4-dione (DMO). Addition of Ca^2+ or K^+ to external media had no effect on the response of net uptake to monensin. Segments taking up [1-^14C]IAA at an enhanced rate in the presence of monensin continued to do so in monensin-free buffer. It is proposed that monensin had no effect on the catalytic activity of the efflux carrier.
University of Southampton
1993
Wilkinson, Sally
(1993)
Interactions between auxin efflux carriers and NPA receptors in higher plant cells.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Phytotropins such as N-1-naphthylphthalamic acid (NPA) are potent non-competitive inhibitors of the efflux of indole-3-acetic acid (IAA) from higher plant cells, and of polar auxin transport. Little is known about mechanisms by which components of the efflux carrier/NPA receptor complex are targeted to, or turned over in the plant cell plasma membrane. Intracellular protein targeting (monensin) and translation (cycloheximide - CH) inhibitors were used to probe this system.
Monensin stimulated the net uptake of [1-14C]IAA by small segments of light-grown pea internode (Pisum sativum L.) or dark-grown zucchini hypocotyl (Cucurbita pepo L.) after a time lag of 20 minutes. It eliminated the typical biphasic response of [1-14C]IAA net uptake to increasing concentrations of competing unlabelled IAA, it inhibited polar IAA transport in long stem segments, and it inhibited the efflux of [1-14C]IAA from preloaded tissue segments within 20 minutes. Uptake carrier activity was not reduced by 10-6 (pea) or 10-7 (zucchini) mol.dm-3 monensin. Higher monensin concentrations, and pretreatment of tissue segments with 10-5 mol.dm-3 CH for at least 1h, reduced the response of [1-14C]IAA net uptake to NPA at pH 5.0, but had no effect on uptake in the absence of NPA. However reducing the pHext rescued 3x10-5 mol.dm-3 monensin- and CH-induced stimulations of IAA net uptake. Both compounds inhibited the efflux of IAA from preloaded tissue segments, but stimulatory effects of reduced efflux on net uptake are proposed to be masked by concomitant inhibitory effects of monensin and CH on other components of IAA net uptake, which contribute more to this when the pHext is greater than 5.0. Neither monensin nor CH affected the net uptake of the ΔpH probe [2-^14C]5,5-dimethyl-oxazolidine-2,4-dione (DMO). Addition of Ca^2+ or K^+ to external media had no effect on the response of net uptake to monensin. Segments taking up [1-^14C]IAA at an enhanced rate in the presence of monensin continued to do so in monensin-free buffer. It is proposed that monensin had no effect on the catalytic activity of the efflux carrier.
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Published date: 1993
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Local EPrints ID: 462335
URI: http://eprints.soton.ac.uk/id/eprint/462335
PURE UUID: 9875f048-c95b-4d2f-a6a7-1f93adbc37bc
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Date deposited: 04 Jul 2022 19:05
Last modified: 04 Jul 2022 19:05
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Author:
Sally Wilkinson
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