Experiments on the fluoroacetate metabolism of Dichapetalum cymosum (Gifblaar)

It was shown that application of fluoroacetate to leaf disks of Dichapetalum cymosum (Gifblaar) did not lead to an inhibition of oxygen uptake or accumulation of citrate, in contrast to the 'control plant' Parimarium capense which lacks fluoroacetate. The addition of fluorocitrate did, however, inhibit the oxygen uptake of both plants and caused an accumulation of citrate. From the results it was deduced that either citrate synthetase or acetate thiokinase from D. cymosum had different affinities for the fluorinated derivative and the 'normal' metabolite. The addition of fluoropyruvate to leaf disks caused a decrease in oxygen uptake and no change in the citrate concentration. From this it was deduced that fluoropyruvate inhibited pyruvate oxidase in both plants. It was concluded that the tolerance of D. cymosum to such high concentrations of fluoroacetate may be ascribed to the fact that the 'lethal synthesis' of fluorocitrate does not take place in the plant most probably because citrate synthetase has different affinities for fluoroacetylcoenzyme A and acetylcoenzyme A.