The effects of 2,4-dinitrophenol and chemical modifying reagents on auxin transport by suspension-cultured crown gall cells

1. The effects of 2,4-dinitrophenol (DNP) and chemical modifying reagents on the transport of indol-3-yl acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4 D) by suspension-cultured crown gall cells of Parthenocissus tricuspidata Planch. were investigated. 2. DNP smoothly reduced uptakes of both benzoic acid and 2,4 D but IAA uptake at pH 6.0 was not inhibited by concentrations below 20 mol/l except in the presence of 2,3,5-triiodobenzoic acid (TIBA) whose stimulatory effect was thereby abolished. DNP stimulated the efflux of 2,4 D and of IAA in the presence of TIBA. Without TIBA, DNP first inhibited but later stimulated IAA efflux. —3. Low concentrations of N-ethylmaleimide (NEM) (<5 mol/l) abolished TIBA-stimulation of net IAA uptake while not affecting (or slightly promoting) net uptake of IAA alone, whose inhibition needs greater NEM concentrations. Diethylpyrocarbonate behaved similarly. The poorly-penetrant p-chloromercuriben-zenesulphonic acid did not cause a marked differential inhibition of the TIBA stimulation. — 4. Together with earlier data, the results support a two-carrier model comprising a common carrier for IAA and 2,4 D, previously suggested to be an auxin anion/proton symport, and also an electrogenic carrier, specific for IAA anions, and inhibited by TIBA. The role of such carriers in polar auxin transport is discussed.Abbreviations IAA Indol-3-yl acetic acid - 2,4 D 2,4-Dichlorophenoxyacetic acid - BA Benzoic acid - DNP 2,4-Dinitrophenol - NEM N-ethylmaleimide - PCMBS p-Chloromercuribenzenesulphonic acid - TIBA 2,3,5-Triiodobenzoic acid