Convenient screening of 4-hydroxyphenylpyruvate dioxygenase inhibitors by UV absorbance detection in the presence of Fe2+ ion

4-Hydroxyphenylpyruvate dioxygenase (4-HPPD), one of the target enzymes for bleaching herbicides, was known to be deactivated by making a Fe2+-chelate combination with inhibitors at its active site. Complexation abilities of 1-phenylbutane-1,3-dione derivative, 2-cyano-4-phenylbutane-1,3-dione derivative, benzoylcyclohexane-1,3-diones and benzoylpyrazole derivatives with Fe2+ was demonstrated by spectrophotometric analysis under different concentrations of iron (II) sulfate aqueous solution. The active forms of pyrazolate in the presence of Fe2+ showed large changes in UV absorbance, whereas no apparent changes were observed with non 4-HPPD inhibiting compounds. UV analysis using iron (II) sulfate aqueous solution was a convenient method before 4-HPPD-inhibiting assay and pot test with intact plants in the screening of novel candidates for 4-HPPD inhibitors.