Herbicide induced peroxidations

Quantitative estimation indicates that only about 1% of peroxidized a-lin is decomposed to ethane or ethylene (5 ) However, the high sensitivity of gas-chromatography for volatile hydrocarbons and the advantage that this determination can be done with intact organisms make short-chain hydrocarbons excellent markers to trace herbicide-induced peroxidation reactions. 

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). 

Diphenylethers. Different agents can induce peroxidations in photosynthetic membranes. The strongest peroxidative herbicides known are the p-nitrodiphenyl ethers. Although compounds from this group of herbicides can act multifunctionally as electron-transport inhibitors U, 2 ) and energy-transfer inhibitors (1 0), some of them, like oxyfluorfen, exert their dominant phytotoxic action by damaging membrane components. 

Lipid peroxidation, herbicides that induce, 13 297-298 Lipids... 

The accumulated ACC appears to be transported to the shoot, where it induces more synthesis of ACC which is converted to ethylene and cyanide. Treatment of isolated shoots with ACC via the vascular system stimulated ACC synthase activity and ethylene and cyanide production [7,37,49,51]. Cyanide was formed as a coproduct of ethylene in the oxidation of ACC, catalyzed by ACC oxidase [14,52]. While quinclorac-induced increases of ABA and hydrogen peroxide are not enough to elicit herbicidal effects [7], cyanide levels in the grass shoot tissue accumulated according to the herbicide concentration and application time and closely correlated with phytotoxicity... 

There are three initiation mechanisms for the free radical lipid peroxidation in the living cells. At the first lipoperoxidation in the body can be induced by non-enzymatic mechanism. In this processes different physical factors such as ionizating irradiation or UV radiation as well as action of some chemical toxicants including air pollutants, pesticides and herbicides from food and drinking water may act as a initiating factors. 

A peroxisome proliferator is a chemical that induces peroxisome proliferation in rodent liver and other tissues and includes a wide range of chemicals such as certain herbicides, plasticizers, drugs, and natural products [38,39], The peroxisomes contain hydrogen peroxide and fatty acid oxidation systems important in lipid metabolism and activation of the peroxisome proliferator-activated receptor alpha (PPARa), is considered a key event in peroxisome proliferation in rodent hepatocytes [39], A number of studies have identified... 

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. 

Besides the bleaching cause by either carotene inhibition or peroxidation more targets for "bleaching herbicides" are conceivable, e.g., interference with chlorophyll formation itself. DTP, a substituted pyrazole, was reported to induce chlorosis by blocking... 

Methyl - 4 - phenyl -1,2,3,6 - tetrahydropyridine (MPTP) is a frequently used animal model for Parkinson s disease. When injected into animals, MPTP is taken up by the cells in the substantia nigra where monoamino oxidase B (EC 1.4.3.4) converts it to l-methyl-4-phenylpyridinium ion (MPP ). This ion induces free radicals and duplicates many of the signs of Parkinson s disease in animals. In mice melatonin attenuated the resulting damage in the central nervous system (Acuna-Castroviejo et al. 1997). MPTP-induced neural lipid peroxidation was reduced to control levels when melatonin was co-administered with the herbicide. Neuronal loss and MPTP-induced reduction of tyrosine hydroxylase (EC 1.14.16.2) activity in neurones of the striatum were attenuated by melatonin. 

Table 5.2 shows examples of the major NDPE herbicides, and Figure 5.8 shows examples of other classes of miscellaneous herbicides whose mode of action has been considered identical to that of NDPEs based on their similar symptomology. The typical symptoms of these compounds are similar to those of paraquat. They cause a light-dependent, rapid chlorosis and necrosis due to a rapid induction of peroxidative degradation of cellular constituents, particularly membrane lipids. Several ultrastructural studies have revealed that the NDPEs and other compounds (oxadiazon, LS 82-556, M B 39279) show distinct differences in the sequence of ultra-structural damage compared to that induced by paraquat. ... 

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