Atrazine metabolism in corn seedlings

Atrazine is a herbicide widely used in corn culture. Corn seedlings metabolize this active ingredient readily in three ways. Two of them are catalysed by enzymes and another is purely chemical. In seedlings, the precise role played by each of these was still not clearly understood. Our work demonstrates that the chemical pathway leading to the formation of the inactive OH-2 atrazine is the pre-eminent form of metabolization inside the roots and, during the first week, inside the leaves. As shown by the kinetics of accumulation of the benzoxazinones responsible for this metabolization, a high potential of atrazine hydroxylation remains effective inside the leaves for at least 1 month. The OH-2 atrazine, which seems to accumulate inside the cell vacuoles, cannot move freely inside the plant and therefore cannot be abundantly transported from roots to leaves. The formation of a glutathione-atrazine conjugate, due to the activity of a glutathione-S-transferase (GST) isoenzyme, represents only a very small part of the total GST in corn. It is mostly present in the aerial parts and is highly effective only after a 1-week culture. When analysing the mixture of the metabolites formed in isolated corn leaves, which is very complex (nine products, among which six were major products), it seems that the metabolization pattern of corn leaves is the combined result of the three pathways and of the transformation of the conjugate into more simple derivatives.