ATRAZINE METABOLISM SELECTIVITY AND MODE OF ACTION

The primary atrazine-sensitive site seems to be located within the chloroplast for resistant as well as susceptible plants. Atrazine inhibits the Hill reaction and its associated noncyclic photophosphorylation, while being ineffective against cyclic photophosphorylation. N-Dealkylation causes a decrease in the inhibitory activity of atrazine, but the same reactions mentioned above were inhibited despite the change in molecular structure. Atrazine readily penetrates the chloroplasts of resistant as well as susceptible plants and seems to accumulate there until an equilibrium concentration is attained between the chloroplasts and the cytoplasm. In resistant plants such as sorghum, metabolism of atrazine very likely occurs outside the chloroplasts to form water-soluble compounds and insoluble residue, reduces the concentration of the photosynthetic inhibitor in the chloroplasts, and results in a recovery of photosynthesis. Changes in solubility of the parent atrazine, caused by its metabolism, may be of great significance in the tolerance of plants to the herbicide. © 1969, American Chemical Society. All rights reserved.