Inhibition of Phytoene Desaturase — the Mode of Action of Certain Bleaching Herbicides

Assay systems have been developed in order to differentiate between the m odes o f action o f certain bleaching herbicides. These include inhibition o f chlorophyll or carotenoid biosynthesis, and initiation o f pigment degradation. Herbicidal com pounds with phytoene desaturase as their primary target site were investigated in a cell-free carotenogenic system from Aphanocapsa. In a comparative study, the structural prerequisites for inhibition o f phytoene desaturase were estab­ lished for both benzophenone analogs and various m -phenoxybenzam ides. This inhibitory action of the latter compounds is enhanced by lipophilic groups with certain steric properties.