Organic acids are known phytotoxins in some anaerobic waterlogged soils. In this work, we tested the
influence of hexanoic acid (HxA) on pea roots. HxA had an inhibitory effect on root tissue O2 consumption
but only at pH 5.0, not at pH 6.0. Intact root tissues exposed to 20 mM HxA for 1 h showed solute leakage.
Mitochondria were isolated from pea roots after 1 h incubation in the presence or absence of HxA, at either
pH 5.0 or 6.0. The maximum effect of HxA on was detected at pH 5.0 in the presence of succinic acid
and without BSA in the assay buffer. A smaller effect was induced by HxA at pH 5.0 with malic plus
glutamic acids, while at pH pH 6.0 no effect was observed. Mitochondrial respiration was affected by HxA
after root incubation at pH 5.0. The decrease of respiration was induced by HxA with both succinic acid and
malic plus glutamic acids but BSA in the assay buffer enhanced the effect of HxA, at least with succinic
acid. These findings strongly suggest that the toxicity of HxA is caused by its un-dissociated form, affecting
plasmalemma permeability and mitochondrial activities.
