Mode of action of new diethylamines in lycopene cyclase inhibition and in photosystem II turnover

The new bleaching herbicidal compound N,N-diethyl-N-(2-undecynyl)amine (NDU A) is identified here as an inhibitor of lycopene cyclase and is compared w ith the known cyclase inhibitors N,N-diethyl-N-[2-(4-chlorophenylthio)ethyl ]amine (CPTA) and N,N-diethyl-N-[2-(4-methylphenoxy)ethyl]amine (MTPA). HPL C separation of chloroplast pigments shows lycopene accumulation in NDUA tr eated tissue. Variation in chain length of the undecynylamine moeity of NDU A from 7 to 21 C atoms reveals an optimum of 11 to 14 C atoms for herbicida l activity. A series of seven further analogues of NDUA and CPTA reveals th e structural elements necessary for inhibition of lycopene cyclase, The eff ect of NDUA derivatives on photosynthesis has been studied in Chlamydomonas reinhardtii. Photosynthesis is highly sensitive, particularly towards the C14 and longer chain length analogues at nanomolar concentrations. It is sh own that the breakdown of photosynthesis by NDUA is due to interference wit h the turnover of the D1 protein of the photosystem II reaction centre that requires the continous biosynthesis of the two reaction-centre beta -carot ene moieties in the reassembly phase. The D1 protein disappearance is most marked under strong light conditions. The depletion of photosystem II occur s before total pigment bleaching. This newly recognized mechanism in herbic idal activity is also the basis for the mode of action of other lycopene cy clase inhibitors as well as phytoene desaturase inhibitors. (C) 2001 Societ y of Chemical Industry.