The e.s.r. method has been used to study the effect of a number of pyridazinone derivatives; l-phenyl-4-amino-5-chloro- (I), 1-phenyl-4,5-dichloro- (II), 1-phenyl-4-nitro-5-hydroxy- (III), 1-phenyl-4-amino-5-bromo- (IV) and 1-phenyl-4-nitro-5-chloro-(V)-pyridazinone-6 on the redox conversions of P700 in wheat and bean leaves a nd isolated chloroplasts. It is shown that in isolated chloroplasts the derivatives I, II and IV are strong inhibitors of electron transport and III and V weak. The site of inhibition - the reducing side of photosystem II (p.s.-II) - is close to the site of action of diurone. In the leaves of wheat seedlings, inhibition of electron transport in vivo by the derivatives I, III and IV is accompanied by the formation of a "dark" e.s.r. singlet signal with g = 2·0040 and width 0·8 m T1. It is shown that a similar signal appears on irradiation of the leaves with shortwave ult raviolet. Having regard to the e.s.r. characteristics, this signal is assigned to the s ignal of endogenous phenols.
|Number of pages||8|
|Publication status||Published - Dec 1 1985|
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