Electron inhibition, photosynthetic

Herbicides that inhibit photosynthetic electron flow prevent reduction of plastoquinone by the photosystem II acceptor complex. The properties of the photosystem II herbicide receptor proteins have been investigated by binding and displacement studies with radiolabeled herbicides. The herbicide receptor proteins have been identified with herbicide-derived photoaffinity labels. Herbicides, similar in their mode of action to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) bind to a 34 kDa protein, whereas phenolic herbicides bind to the 43-51 kDa photosystem II reaction center proteins. At these receptor proteins, plastoquinone/herbicide interactions and plastoquinone binding sites have been studied, the latter by means of a plastoquinone-deriv-ed photoaffinity label. For the 34 kDa herbicide binding protein, whose amino acid sequence is known, herbicide and plastoquinone binding are discussed at the molecular level. 

Its mode of action is similar to other photosynthesis inhibitors in that its activity is dependent on light. It inhibits photosynthetic carbon dioxide fixation and photosynthetic electron transport. 

Bromoxinil or 3,5-dibromo-4-hydroxybenzonitrile Benzonitrile Inhibits photosynthetic electron transport, selective for certain annual broad leave weeds Cereals, maize, sorghum, turf 11-2... 

The natural product cyanobacterin has been found to inhibit photosynthetic electron transport in other organisms. A series of analogs of cyanobacterin were prepared as potential herbicides. Several of the analogs also inhibit the growth of the test photosynthetic organisms. The synthesis and structure-activity relationships of these analogs are discussed. 

A variety of herbicides kill plants by inhibiting photosynthetic electron transport. QUESTION 13.9... 

Almost all of the carbamate herbicides inhibit photosynthesis, as has been shown by the investigations of Moreland and Hill (1959). Asulam and terbutol do not inhibit photosynthetic electron transport in vitro, while the other carbamates do only in high concentrations not occurring in vivo. The conclusion of Corbett (1974), that the inhibition of photosynthesis is only a side-effect of these compounds, therefore seems justified. 

Metribuzin represents the herbicides that inhibit photosynthetic electron transport shortly after photosystem II ( ). 

Many compounds, including a number of commercial herbicides, are known to inhibit photosynthetic electron transport (PET) close to the photosystem 11 (PSj,q ) reaction centre (RC) in plant chloroplasts. Such PET... 

Incubation of leaf discs in LY181977 causes an increase in chlorophyll fluorescence similar to that caused by atrazine and diuron (Figure 2). Similarly the IC50 for DCPIP reduction by isolated spinach thylakoids is similar for LY181977 (0.73 pM) and atrazine (0.36 pM). This indicates that LY181977 inhibits photosynthetic electron transport through photosystem II with efficacy similar to that of atrazine. 

The data presented here indicates that LY181977 inhibits photosynthetic electron transport through photosystem II. LY181977 has some interaction with that portion of the herbicide binding site which confers atrazine resistance in mutant DCMU4. 

Methabenzthiazuron is a preemergence herbicide, urea derivative and photosynthetic inhibitor that inhibits photosynthetic electron transport at the diuron site . After treatment with this herbicide, the wheat crop showed physiological effects , such as a delayed senescence of leaves, a greening effect and a decrease in carbohydrate content. 

A different and more specific approach has been used by Radunz and coworkers. They have prepared a series of lipid-specific antibodies to various chloroplast lipids. The antisulfolipid serum was found to inhibit photosynthetic electron transport of stroma-free chloroplasts in the region of light reaction 1. The inhibition was restricted to the same pH range as the nonco-valent binding of sulfolipid to thylakoid polypeptides, which increased the latter s a-helical content (Menke et al., 1976). 

The desaturation of newly synthesized fatty acids apparently proceeds within the plastids or in part also in the cytoplasm. Substituted pyridazinones can have multiple sites of action. Some of them effectively inhibit photosynthetic electron transport and others the carotenoid biosynthesis (Lichtenthaler and Kleudgen 1977).Some of these also block the desaturation of fatty acids. The desaturation of linoleic acid was proposed to be one target (St. John 1976). Treated plants show a higher 18 2/18 3 ratio than untreated plants. Furthermore some pyridazinones inhibit the desaturation of P6 16 0 to PG 16 1 (3-trans) (Khan et al. 1979). Khan proposed that the blocked desaturase may be plastidic, which was proved for Arabidopsis (Norman and St. John, 1987). In general different pyridazinones may act on different desaturases with different l g-values. Another important point is the changed 18 2/18 3 ratio, which may cause a decreased frost-hardening (Fedtke 1982). 

Antisera to constituents of the thylakoid membrane such as to glycolipids, phospholipids as well as to carotenoids inhibit photosynthetic electron transport in the region of photosystem I as well as of photosystem II. The degree of inhibition differs with the individual antisera used. If the degree of inhibition in the region of photosystem I and photosystem II is... 

The development of herbicides that inhibit photosynthetic electron transport has proved to be outstandingly successful. Furthermore, because of the efficiency of these compounds and their use as tools to study photosynthesis, our knowledge of photosystem II in particular has been greatly enhanced by their use. Recent developments involving X-ray structural analysis of photosynthetic bacterial reaction centers as well as the ability to engineer herbicide resistance into crop plants have been outstanding scientific achievements. 

As mentioned earlier, a great deal of literature has dealt with the properties of heterogeneous liquid systems such as microemulsions, micelles, vesicles, and lipid bilayers in photosynthetic processes [114,115,119]. At externally polarizable ITIES, the control on the Galvani potential difference offers an extra variable, which allows tuning reaction paths and rates. For instance, the rather high interfacial reactivity of photoexcited porphyrin species has proved to be able to promote processes such as the one shown in Fig. 3(b). The inhibition of back ET upon addition of hexacyanoferrate in the photoreaction of Fig. 17 is an example of a photosynthetic reaction at polarizable ITIES [87,166]. At Galvani potential differences close to 0 V, a direct redox reaction involving an equimolar ratio of the hexacyanoferrate couple and TCNQ features an uphill ET of approximately 0.10 eV (see Fig. 4). However, the excited state of the porphyrin heterodimer can readily inject an electron into TCNQ and subsequently receive an electron from ferrocyanide. For illumination at 543 nm (2.3 eV), the overall photoprocess corresponds to a 4% conversion efficiency. 

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