Competition between a thiocarbamate herbicide and herbicide protectants at the level of uptake into maize cells in culture

The rapid interactions between the herbicide S-ethyl dipropyl thiocarbamate (EPTC) and the structurally similar herbicide protectant N,N-diallyl 2,2-dichloroacetamide (DDCA) at the level of herbicide uptake were examined in maize cell cultures. When the two compounds were given simultaneously, DDCA inhibited uptake of [¹⁴C]EPTC into maize cells measured for 30 min. A Lineweaver-Burk plot indicated this inhibition to be competitive. N,N-Diallyl 2-chloroacetamide (CDAA), a compound similar in structure to DDCA, inhibited uptake to a lesser extent. Other protectants having no similarity in structure to either DDCA or EPTC had no inhibitory effect on the uptake of EPTC. The data suggest that competition between DDCA and EPTC for a site of uptake may be related to their similarity in chemical structure. Experiments with metabolic inhibitors suggested that uptake of EPTC is not via an active transport mechanism. We suggest that competition for uptake between EPTC and DDCA may represent the first step in a complex series of interactions between the herbicide and its protectant that contributes to the protection of maize from herbicide injury.