Differential atrazine interference with the Hill reaction of isolated chloroplasts from Chenopodium album L. biotypes

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Abstract
Summary: Atrazine [2‐chloro‐4‐(ethylaminol‐6‐(isopropyl‐amino)‐s‐triazine] resistant biotypes of lamb's quarters (Chenopodium athum L) were reported in the maize growing areas of Ontario, where the herbicide had been used fur a number of years. Field samples from four locations proved tolerant to higber than recommended rates of atrazine in controlled environment screening trials. A resistant biotype was not killed with up to 40 kg/ha atrazine. Diuron at 5 x10‐5 M inhibited the Hill reaction with isolated chloroplasts of resisiant and susceptible biotypes of lamb's‐quarters. However, with 10‐4 M atrazine, the photochemical activity was inhibited in chloroplasts isolated from the susceptible biotype but not in chloroplasts from the resisiant biotype. With maize chloroplasts, inhibition with 10‐4 M atrazine was the same as with the susceptible biotype of lamb's‐quarters. These studies suggested that a new mechanism of intraspecific resistance in lamb's quarters to atrazine was involved, other than differences in uptake, translocation and metabolism reported with interspecific comparisons involving the s‐triazines and other herbicides, It was also concluded that atrazine and diuron did not have precisely the same mechanism of action as photosynthetic inhibitors with lamb's‐quarters, and that external and or internal structure or function of chloroplasts in relation to atrazine inhibition can vary significantly even in biotypes of the same species.