Toxicological sensitivity of Pennisetum americanum (L.) K. Schum to atrazine exposure.

The tolerance of Pennisetum americanum (L.) K Schum (P. americanum) to the herbicide atrazine, as well as the atrazine accumulation in exposed plants, was investigated in this study. The germination of P. americanum seeds was not significantly inhibited by exposure to atrazine at concentrations below 100 mg·L-1. The roots of the seedlings were much more sensitive to atrazine than the shoots were, as shown by observations that shoot and root elongation were significantly inhibited by treatment with 100 and 50 mg·kg-1 of atrazine, respectively. In addition, significant differences were found in the dry weights of the seedling shoots and roots after exposure to 50 and 20 mg·kg-1 of atrazine, respectively. Atrazine accumulated readily in the roots of exposed seedlings, and the root ultrastructure was visibly damaged by exposure to lower levels of atrazine compared to the ultrastructure of the shoot. The contents of chlorophyll a and chlorophyll b and the transcription of psbA were inhibited by exposure to atrazine at concentrations above 20 mg·kg-1. Finally, the tolerance threshold of P. americanum to atrazine was about 20 mg·kg-1, indicating that the test plant exhibited some atrazine tolerance.