Figure 6.

Time course of atrazine metabolism in excised leaves of corn and MCR, ACR, and WCS waterhemp populations. Excised leaves (third youngest leaf; 2–3 cm in length) from waterhemp (10–12 cm) or corn seedlings were placed in 0.1 m Tris-HCl buffer (pH 6.0) for 1 h, followed by 0.1 m Tris-HCl (pH 6.0) plus 150 μm [U-¹⁴C]atrazine for 1 h, then one-quarter-strength Murashige and Skoog salts solution for 0, 3, or 11 h. Data were analyzed by nonlinear least-squares regression analysis and fit with a FOMC model (Gustafson and Holden, 1990) to estimate a DT₅₀ separately for each waterhemp population and corn. The DT₅₀ values of atrazine determined by regression analysis were 0.6 h (95% confidence interval of 0.3–0.9) in corn, 2.2 h (95% confidence interval of 1.1–3.2) in MCR, 2.2 h (95% confidence interval of 1.1–3.2) in ACR, and greater than 12 h in WCS.