Absorption and efflux of chloro‐s‐triazines by <i>Setaria</i> roots*

Abstract

Summary: The absorption and loss of four chloro‐s‐triazines was investigated in excised roots of four Setaria taxa. Different taxa absorbed the various triazines at different rates. In general, triazine absorption was greater at 2°C than at 22.5°C, and absorption rates were linear functions of external concentrations. Efflux studies showed marked differences in the rate of loss of 14 C‐atrazine, 14 C‐simazine, and 14 C‐propazine from root sections of robust white foxtail ( Setaria viridis var. robustaalba Schreiber). The roots lost 14 C‐atrazine very quickly, and the loss was similar in either water or 12 C‐atrazine. Atrazine appears to be restricted to the apoplast of the root. 14 C‐atrazine was lost more rapidly than either 14 C‐simazine or 14 C‐propazine to water or to solutions containing the unlabelled herbicide. Efflux of 14 C‐simazine was greater than that of 14 C‐propazine to solutions of CaCl 2 . From the pattern of efflux, it was concluded that 14 C‐simazine and 14 C‐propazine accumulated in the root symplast. Furthermore, the decreases in chloro‐s‐triazine absorption in the presence of metabolic inhibitors (dinitrophenol, sodium arsenite) may suggest that 14 C‐simazine and 14 C‐propazine entered the symplast by an energy‐dependent process.