EFFECTS OF N,N'-DIBUTYLUREA ON PHOTOSYNTHETIC ELECTRON-TRANSPORT REACTIONS IN ISOLATED-CHLOROPLASTS

N,N'-dibutylurea, a secondary, accumulative degradation product of the fungicide benomyl, was investigated to determine its effects on the e lectron transport system in isolated chloroplasts. Dibutylurea was fou nd to inhibit photosynthetic oxygen evolution, photo-induced reduction of ferricyanide, and reduction of NADP. It produced a sigmoidal dose response for inhibition of ferricyanide reduction with an I-50 Of 167 mu M. Other symmetric alkylureas were found to only weakly inhibit fer ricyanide reduction regardless of the dose applied. Dibutylurea produc ed a dose response for electron transport inhibition when applied to K CN/Hg-inhibited chloroplasts and inhibited NADP reduction in the prese nce of 1 mu M DBMIB and a TMPD bypass. These results suggest dibutylur ea inhibits photosynthetic electron transport in a manner similar to k nown PSII inhibitors, with the possible site of action in PSII on the reducing side of the Q(B) protein complex. (C) 1998 Academic Press.