Hydrogen ion dependence of carrier-mediated auxin uptake by suspension-cultured crown gall cells |
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Authors: | P H Rubery |
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Institution: | (1) Department of Biochemistry, University of Cambridge, Tennis Court Road, CB2 1QW Cambridge, UK |
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Abstract: | 1. The dependence on external hydrogen ion concentration of the carrier-mediated components of the uptakes of indol-3-yl acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4D) by suspension-cultured crown gall cells from Parthenocissus tricuspidata Planch. is examined. The initiall rates of uptake of IAA and 2,4 D from 0.30 mol/l solutions exhibit pH optima of approximately pH 5.0 and pH 4.0 respectively.-2. The inherent difficulties, especially at low pH, of estimating the carrier-mediated uptake component in the presence of the large diffusive uptake of undissociated acid are discussed.-3. At pH 5.0, the uptakes of the two auxins are characterised by similar Michaelis Constants (0.65 and 0.80 mol/l) and Maximum Velocities (0.87 and 1.0 pmol/min/mg cells) for IAA and 2,4D respectively.-4. A dependence of carrier-mediated auxin uptake on cations other than hydrogen ions could not be demonstrated. It is suggested that uptake of auxin anions may occur by co-transport with hydrogen ions.Abbreviations IAA
indol-3-yl acetic acid
- 2,4 D
2,4-dichlorophenoxyacetic acid |
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Keywords: | Auxin uptake Crown gall Parthenocissus pH co-transport Suspension culture |
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