Inhibitory Effects of 2,3,5-Triiodobenzoic Acid on Ion Absorption, Respiration, and Carbon Metabolism in Excised Barley Roots

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Abstract
The ability of 2,3,5-triiodobenzoic acid (TIBA) [an auxin antagonist] to alter ion absorption, respiration, carbon metabolism and the permeability of the cell membranes of excised barley roots was examined. Roots pretreated in either H20, KCI or TIBA followed by treatment in KCI, TIBA or KCI and TIBA demonstrated that inhibition of ion uptake due to TIBA was reversible. Ions already accumulated within the vacuole remain sequestered after the addition of TIBA, whereas cytoplasmic ions leak out into the external medium. A 20 min lag period was present prior to the onset of inhibition of 02 consumption by TIBA. A b-type cytochrome from corn that is apparently associated with the plasmalemma and possibly involved in respiration or ion uptake, or both, was unaffected by TIBA. The addition of TIBA treatment solutions resulted in the synthesis and accumulation of ethanol. Analysis of organic acids showed that only the malate concentration was affected by treatment with TIBA. A reduction of 26% was noted for malate in the presence of 2 .mu.M TIBA. The inhibitory action of TIBA in barley roots involves an alteration of mitochondrial respiration, and not a direct depolarization of the plasmalemma.