Phytotoxic peroxidizing actions of cyclohexanedione (RWH-series) derivatives

2-(2-Chloro-5-propyloxycarbonylphenyl)aminomethylidene-5,5-dimethylcyclohexane-1,3 dione (RWH-21), a new photo-bleaching compound, stimulates accumulation of 132-hydroxychlorophyll a in cultured tobacco cells under light and dark conditions. This is based on isolation of 132-hydroxychlorophyll a from pigment extracts of cultured tobacco cells by HPLC and subsequent instrumental analysis. RWH-21 causes lipid peroxidation in tobacco cells, as assessed by the formation of malondialdehyde (MDA) and ethane. Sodium azide, a singlet oxygen scavenger, partially inhibited MDA formation and the bleaching activity of RWH-21 in tobacco cells. Diphenylether-resistant tobacco cells (YZI-1S) did not show tolerance to RWH-21. Our data indicate that RWH-21 has a different mode of action from diphenylethers, and that compounds inducing the accumulation of 132-hydroxychlorophyll a in plant tissues could exhibit photo-bleaching herbicidal actions.