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A comparison between 3,5‐diiodo‐4‐hydroxybenzoic acid and 2,3,5‐triiodobenzoic acid. II. Effects on uptake and efflux of IAA in maize roots
Author(s) -
Martin Hilary V.,
Beffa Roland,
Pilet PaulEmile
Publication year - 1987
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1987.tb04613.x
Subject(s) - efflux , zea mays , elongation , coleoptile , chemistry , stimulation , auxin , horticulture , acetic acid , biochemistry , biology , agronomy , materials science , neuroscience , ultimate tensile strength , gene , metallurgy
An explanation is sought for the inhibition of maize root growth and gravireaction brought about by treatment with 3,5‐diiodo‐4‐hydroxybenzoic acid (DIHB). The effects of DIHB and 2,3,5‐triiodobenzoic acid (TIBA) on the uptake and efflux of [ 3 H]‐indol‐3yl‐acetic acid (IAA) were tested using segments prepared from the elongation zone (2 to 7 mm region) of maize ( Zea mays L. cv. LG11) roots. The uptake of [ 3 H]‐IAA (21 n M ) by root segments incubated in buffered solutions (pH 5.0) was measured over a 5‐min time‐course. No significant effect of DIHB at 100 μ M was observed, whereas TIBA at 10 μ M slightly stimulated the uptake of [ 3 H]‐IAA. This experiment was repeated with the addition of non‐radioactive IAA (total IAA concentration 1.0 μ M ). Up to 3 min DIHB (100 μ M ) had no significant effect, but thereafter a slight stimulation of IAA net uptake was observed. Treatment with TIBA (10 μ M ) stimulated the accumulation of IAA in the segments. The effects of DIHB (10, 50, 100 μ M ) and TIBA (10 and 50 μ M ) on the efflux of [ 3 H]‐IAA from segments that had been pretreated in [ 3 H]‐IAA (22 n M ) were then tested. Treatment with DIHB or TIBA at pH 5.0 inhibited IAA efflux; the inhibition by TIBA was more marked than that produced by DIHB. This experiment was repeated using DIHB (10, 50, 100 μ M ) buffered at pH 6.0, and an inhibition of IAA efflux was again observed. Both DIHB (10 μ M ) and TIBA (10 μ M ) inhibited the binding of [ 3 H]‐NPA to a 5000–48000 g membrane fraction prepared from whole maize roots. The effects of the two substances were similar: 40% inhibition of specific binding by DIHB and 41% inhibition by TIBA. This indicates that DIHB, like TIBA, binds to the N‐1‐naphthyl‐phthalamic acid‐sensitive carrier for IAA efflux. It is concluded that DIHB, like TIBA, inhibits IAA transport at the level of efflux. The similarity between DIHB and TIBA as regards chemical structure and their inhibitory effects on IAA efflux and NPA binding strongly suggest that they act on the same carrier for IAA efflux across the plasmalemma.