Norflurazon phytoene accumulation

The amount of carotenoids formed by biosynthesis was quantified by the accumulation of the colourless carotenoid phytoene in the presence of the inhibitor, norflurazon. When applied, substantial amounts of this... 

It can be established from these investigations that unlike triazines and diuron, norflurazon damages the photosynthetic system of the plants. The main action is the blocking of carotenoid synthesis, as a result of which carotenoid precursors (phytoene and phytofluene) are accumulated because of the inhibition of dehydrogenation reactions. 

Owing to the similarity of desaturation reactions catalyzed by PDS or ZDS, differentiation in the plant is not easy to detect. Most of the herbicidal inhibitors probably inhibit both, although to a different extent [6j. If strong inhibition of PDS has taken place with accumulation of phytoene, then the compound s ability to inhibit ZDS cannot be seen. Figure 4.1.2 shows that the commercial products primarily inhibit PDS [6, 8, 27-29]. Cell-free studies exemplified by norflurazon and fluridone have shown them to act as reversible noncompetitive inhibitors of PDS [27]. Other PDS active structures are shown below in Table 4.1.2 and in Section 4.1.4.10. 

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