The Physiological Action of 2,4-Dichlorophenoxyacetic Acid on Dandelion, Taraxacum officinale

Abstract

Dandelion roots from untreated plots and plots sprayed with light (120 ppm.), medium (480 ppm.), and heavy (1920 ppm.) applications of 2,4-D were taken before treatment and at 5-day intervals thereafter for 25 days. Each lot of roots was analyzed for carbohydrate and N compounds, and the rate of respiration was also detd. The reducing sugar content more than doubled and remained high with the medium and heavy treatments, while the light treatment caused a small temporary increase. The sucrose content decreased slowly after treatment while the reserve polysaccharides decreased rapidly, but the loss was not sufficient to suggest a direct cause of death. The non-protein N content increased after treatment, the light and medium concs. of 2,4-D giving the greatest effect. The protein N increased slightly, the medium treatment being the most effective. The rate of respiration increased 25-30% with the light and heavy treatments, dropping to normal after 15 days, while the medium treatment caused a 60-90% increase which remained high. Loss of carbohydrate reserves and decrease in dry wt. were roughly accounted for by increased respiration, indicating no appreciable utilization for growth. The action of 2,4-D is considered to be the result of direct protoplasmic toxicity. The hypothesis is suggested that the toxicity of 2,4-D is directed toward certain cytoplasmic compounds, probably proteins.