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Published online by Cambridge University Press: 12 June 2017
CGA-154281 and temperature effects on metolachlor absorption and metabolism were studied in corn seedlings grown in untreated soil or soil treated with metolachlor, CGA-154281, or both. Seedlings were grown under a cool (21/13 C, 16-h day) or warm (30/21 C, 16-h day) temperature regime and exposed to 14C-metolachlor for 10 min at either 21 or 30 C. Corn grown under the cool temperature regime absorbed slightly more 14C-metolachlor than corn grown under the warm temperature regime. Corn held at 21 C during a 10-min 14C-metolachlor exposure period metabolized metolachlor more slowly than corn held at 30 C. Decreased corn tolerance to metolachlor observed at lower temperatures may be due in part to slower metolachlor metabolism. Corn grown in the presence of metolachlor plus CGA-154281 metabolized 14C-metolachlor to the glutathione conjugate twice as fast as corn grown in the presence of metolachlor alone. The increase in metabolism rate was due to a fivefold increase in glutathione-S-transferase (GST, EC 2.5.1.18) activity and not to an increase in glutathione (GSH) content. Results are consistent with the hypothesis that CGA-154281 protects corn from metolachlor injury by enhancing GST activity, which accelerates metolachlor detoxification via GSH conjugation.