Peroxidizing herbicides measurement

A method of detecting herbicides is proposed the photosynthetic herbicides act by binding to Photosystem II (PS II), a multiunit chlorophyll-protein complex which plays a vital role in photosynthesis. The inhibition of PS II causes a reduced photoinduced production of hydrogen peroxide, which can be measured by a chemiluminescence reaction with luminol and the enzyme horseradish peroxidase (HRP). The sensing device proposed combines the production and detection of hydrogen peroxide in a single flow assay by combining all the individual steps in a compact, portable device that utilises micro-fluidic components. 

Data on herbicides are presented and reviewed, which allows the distinction between two different modes of bleaching. The first mode is caused by inhibited carotene biosynthesis exhibited by particular phenylpyridazinones, substituted phenylfuranones or amitrole. Decrease of carotenes leads to subsequent photodestruction of chlorophyll, peroxidation of other membrane components, and decay of electron transport activity. The second mode, represented by p-nitrodl-phenylethers, is associated with peroxidation of membrane-bound polyunsaturated fatty acids concurrently with the breakdown of carotenes, chlorophylls, and decay of photosynthetic electron transport. Short-chain hydrocarbon gases are reliable markers. The action of peroxidizing diphenylethers appears to be related to that of bipyridylium salts, although no light-induced oxygen uptake can be measured. 

The peroxidative reactions were mediated and sustained by Cu(II) ions in the light. Table IV shows that fatty acids with at least 2 double bonds are necessary for hydrocarbon formation. As Anacystis lacks those fatty acids, no peroxidative volatile hydrocarbons were produced. Spirulina exclusively contains CO-6 fatty acids as endogenous polyunsaturated fatty acids and evolved Cs hydrocarbons only. The third species, Anabaena, whose thylakoids contain co-3 and Co-6 polyunsaturated fatty acids formed C2 and C5 hydrocarbons simultaneously. We conclude that co-3 polyunsaturated fatty acids are the source of ethane and ethylene and that the CO-6 polyunsaturated fatty acids are the source of pentane and pentene in herbicide-induced peroxidation reactions. Furthermore, we obtained evidence that the propane measured with Bumilleriopsis after an 18-h treatment with either 10 >iM oxyfluorfen or 50 jxM Cu(II) originates from a CO-4 polyunsaturated fatty acid. We have recently isolated and identified this acid as 16 3CO4 (Sandmann, Lambert, B5ger in preparation). 

The total amount of porphyrins that accumulate in diphenyl ether-treated tissues is considerably higher than that which accumulates in untreated tissues (fiZ). Therefore, these herbicides appear to increase carbon flow into this pathway. Heme is known to feedback inhibit this pathway and PPIX is required for heme synthesis (9). Feeding heme to diphenyl ether-treated plant cells reduces the amount of porphyrin-caused lipid peroxidation of cell homogenates as measured by oxygen consumption (Ifl). 

Fig. 13.4 Example of calibration of the iimnunosensor for the herbicide 2,4-D (2,4-dichlorophe-noxyacetic acid). The series of the cathodic cmrent-time recordings was obtained using a Au electrode with covalently bound 2,4-D an anti-2,4-D Ab-HRP conjugate served as tracer. Measurements were carried out at —50 mV in a flow-through mode with iodide/hydrogen peroxide mixture. The same immunosensor was used repeatedly and regeneration was carried out using pepsin, adapted from reference (16)...

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