Metabolic Sites of Action of Fluridone in Isolated Mesophyll Cells

Time- and concentration-course studies were conducted to determine the metabolic sites of action of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in isolated mesophyll cells of cotton (Gossypium hirsutumL. ‘Acala SJ-1′) and red kidney bean (Phaseolus vulgarisL.). Cotton is resistant and bean is susceptible to fluridone. The herbicide was not metabolized in cells of either species during the 2-h incubation period. At the highest concentration (10-4M) and longest incubation time (2 h), fluridone inhibited photosynthesis, RNA synthesis, and protein synthesis 59, 56, and 32%, respectively in bean and 24, 21, and 14% in cotton. Lipid synthesis and dark respiration were only slightly affected. The lowest concentration and the shortest incubation period that inhibited photosynthesis, RNA synthesis, and protein synthesis in bean did not have any significant effect in cotton. The difference in responses may contribute to the selectivity of the herbicide. Although photosynthesis appeared to be the primary site of action, RNA synthesis was also markedly inhibited. These inhibitions and the somewhat lower inhibition of protein synthesis may ultimately contribute to the herbicidal action of fluridone in the intact plant.