PSII inhibitors

However, our limited experience with natural products indicates that there may well be a natural product that has the optimal properties. Among a very limited number of natural products, we found anthraquinone, 2-methylanthraquinone, juglone, and sorgoleone to be two to three orders of magnitude more toxic to O. perornata than to S. capricornutum [93]. These compounds are either known [128,143] or suspected PSII inhibitors. Only the first two of these compounds were active enough to be of interest as cyanobactericides. Whether there is a large difference in binding affinities of these compounds for D-l versus L or some other mechanism of selectivity is unknown. 

Two other Lolium ri dum biotypes from Australia (WLR2 and VLR69) developed metabolism-based resistance to PSII inhibitors. WLR2 came from a field with selection pressure by atrazine and amitrole, but never by phenylureas, and VLR69 from a field with selection pressure by diuron and atrazine. Both biotypes were resistant to triazines, and, despite the field selection by atrazine, resistance was more pronounced to the structurally related simazine. Furthermore, both biotypes were resistant to chlorotoluron, though only VLR69 was previously exposed to phenylureas. Analytical work revealed that in both resistant biotypes... 

Examples for PSII inhibitors that have already been included into Annex I are pyridate, isoproturon and bentazone. Table 10.5 exemplifies the provisions that have been imposed for Member States Registration Authorities to address, e.g., by implementation of national use restrictions to ensure these substances are being used safely in the EU Member States. 

Out of a total number of 50 PSII inhibitors, sales could only be recorded in the EU for some 40 compounds. Although the total number of PSII herbicides where sales could be recorded in the EU has only slightly declined from some 40 compounds in 1995 to about 36 compounds in 2004, only ten compounds have yet been included into Annex I as per end of 2005, while the future of a total number of slightly more than 30 PSII compounds still on sale in Europe is unclear or their life has come to an end, for one of the following reasons ... 

As shown in Fig. 2 (lanes B, D) DCMU (3-(3 ,4 -dichlorophenyl)-l,l-dimethylauria) and PpBQ (phenyl-p-benzoquinone) completely abolish PPi dependent protein phosphorylation. Inhibition by the PSII inhibitor DCMU confirms that this phosphorylation is electron transport dependent. Inhibition by PpBQ is consistent with its role as an artificial electron acceptor, leaving the plastoquinone in an oxidized state. This indicates that PQ has to be reduced for the activation of the PPi dependent protein kinase, as is known to be the case with ATP. 

Considerable work during the last few years has identified the genetic basis of PSII inhibitor herbicide resistance and opened up the possibility... 

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