On the Mode of Action of Carbamate Herbicides

The hypothesis of Mann et al. that carbamate herbicides act as anti‐derepressor substances was tested in two systems: cell enlargement and proliferation in cultured tobacco pith, and auxin‐induced Avena first internode extension. Isopropyl‐N‐phenylcarbamate (IPC) and isopropyl‐N‐(3‐chIorophenyl carbamate (CIPC) both severely inhibited kinetin‐induced cell proliferation in tobacco pith at 10−6M. Auxin‐induced tobacco cell enlargement was inhibited to the same degree only at 10−3M. Avena internode extension was insensitive to these compounds in the range 10−3 to 10−7M of IPC and 10−4 to 10−8M CIPC. The results support but do not prove Mann's hypothesis. Results of various studies with carbamates are interpreted in terms of this mechanism.