Factors Affecting Absorption and Translocation of Simazine by Barley

The factors affecting the absorption and translocation of simazine by young barley plants in short-term experiments in water culture have been investigated. Chromatographic examination of the xylem sap indicated no extensive breakdown of the herbicide in the transpiration stream. Under varying conditions of humidity, light intensity, temperature, and in the presence of metabolic inhibitors, the concentration of simazine in the trans piration stream relative to that in the uptake medium was always less than unity. This could, in part, be attributed to retention of simazine at a higher concentration on a fresh weight basis in the root tissues than in the ambient medium. There was little evidence that the absorption and translocation of simazine was influenced by metabolism except in so far as this affected movement of water, and micro-organisms present on the plant roots at ambient laboratory levels had no effect on the uptake and transport of the herbicide. Simazine brings about a decrease in the rate of transpiration and a reduction in the total uptake of rubidium and phosphate at relatively high concentrations. However, when the phosphate concentration in the ambient medium was below the level at which translocation of this ion is affected by the rate of transpiration, the herbicide did not reduce uptake of phosphate. There is therefore no evidence that in short-term experiments simazine has an effect on active transport processes.