Effects of Herbicides and Related Chemicals on Oxidation and Phosphorylation by Isolated Soybean Mitochondria.

Abstract

Herbicides have been shown to affect many diverse processes in plants. Respiratory responses, however, are general, and the idea that a common site of action exists somewhere in the oxidation or phosphorylation systems would seem to be a good working hypothesis (11). In recent years evidence has accumulated that the enzymes involved in aerobic plant respiration and phosphorylation are located in discrete cytoplasmic particles called mitochondria (5, 8). The reactions mediated by these enzymes may be carried out in vitro by properly isolated particles. Although isolated plant particles would appear to be favourable for the study of the effects of herbicides on respiratory enzyme systems, only one referenee (3) to such an investigation has been found. The experiments reported here were carried out with an in vitro particulate system with the hope of further elucidating the mechanism of action of certain herbicides and related chemicals in vivo. The particles used were isolated by differential centrifugation from etiolated soybean hypocotyls and were shown to have oxidative and phosphorylative activities similar to those from mung beans (10). In most experiments treatments consisted of the addition of various concentrations of herbicide or other chemical to Warburg flasks containing the reaction mixture. The effect of the chemical on oxygen uptake by the soybean particles was then expressed as percentage of control (table I). Some of the chemicals tested inhibited oxygen uptake only when added at relatively high concentrations. This suggests an osmotic effect, and probably such an explanation is correct for chemicals that inhibited only at concentrations of 0.1 M or higher, such as sodium chlorate (cf. sodium chloride, table I). Others including 2,4-dichlorophenoxyacetic 1 Received August 23, 1956. 2 Journal Paper No. J-3013 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project No. 944. 3 This research was supported by a Fellowship grant from the Standard Oil Company of Indiana. 4 Present address : Department of Botany, Ontario Agricultural College, Guelph, Ontario, Canada.