Herbicidal activity, accumulation

The result of this is accumulation of phospholipids, or phospholipidosis, in the tissues where accumulation of the drug occurs. Active uptake of a toxic compound into the target tissue may also occur. For example, the herbicide paraquat is actively accumulated in the lung, reaches toxic concentrations in certain cells, and then tissue damage occurs (see chap. 7). 

In the original system of Rebeiz et a/. (5), a rather long post-spray dark period was required for sufficient accumulation of porphyrins for herbicidal activity occur. The herbicidal effect of ALA plus DP was age and species dependent however, there was not always a strong correlation between the effect on porphyrin... 

The earlier study on mode of action of pyrazolate by Kawakubo and Shindo (11) had suggested that the herbicidally active metabolite of pyrazolate blocked protochlorophyllide synthesis by removing Mg from Mg-protoporphyrins. They concluded that the metabolite worked as an acid (donating to chlorophyll) to form pheophytin. We also tried to reconfirm the formation of pheophytin by the metabolite in vivo and in vitro. When it was added to the pigment solution at SkIO M and kept in a dark cold room for 24 hr, a dramatic accumulation of pheophytin (43-fold) with a concomitant depletion of... 

Bialaphos and tabtoxinine-j8-lactam, a Pseudomonas toxin, both cause the accumulation of high intracellular ammonia concentrations in plant tissues.There is also a substantial body of evidence that this aspect of GS inhibition is important in the herbicidal activity of ppj. s-iQs... 

A second class of herbicides primarily affects ( -carotene desaturase. These herbicides are apparent feedback inhibitors of PD as well. This class of compounds includes dihydropyrones like LS 80707 [90936-96-2] (56) and 6-methylpyridines (57,58). The third class consists of the ben2oylcyclohexane-diones, eg, 2-(4-chloro-2-nitroben2oyl)-5,5-dimethyl-cyclohexane-I,3-dione. This class of atypical bleaching herbicides induces phytoene accumulation when appHed either pre- or post-emergence. However, it does not inhibit phytoene desaturase activity in vitro (59). Amitrole also has been considered a bleaching herbicide, though its main mode of action is inhibition of amino acid synthesis. 

Many herbicides and other chemicals have been reported to influence levels of various phenolic compounds in higher plants by unknown mechanisms. It is unlikely that more than a few of these compounds have a primary influence on secondary phenolic compound synthesis. For instance, in our survey of the effects of 17 herbicides on anthocyanin accumulation, only glyphosate appeared to directly influence accumulation (31). The effects of several compounds on secondary phenolic compound production for which the mechanism of influence is unknown are summarized in Table II. A much longer list could be derived from the literature. Unfortunately, many of these compounds are phytotoxic or are known to have effects other than on secondary aromatic compound production. In most cases the effects on these compounds correlate well with extractable PAL activity (31, 71, 72, 73, 74) (Figure 5), even though they do not directly affect the enzyme. 

Carbamates are used as insecticides, nematocides, fungicides, and herbicides the toxicity of carbamate insecticides is similar to that of OP compounds and is based on the inhibition of ACHE. Also, carbamate metabolites may inhibit ACHE but are usually weaker inhibitors than the unchanged compound. Cholinesterase inhibition caused by carbamates is labile, of short duration, and rapidly reversible in fact, the half-life of the inhibited enzymes ranges between some minutes and 2 to 3 hours for RBC-ACHE and is on the order of some minutes for PCHE. Accumulation of cholinesterase activity on repeated exposures, as observed with OP compounds, does not occur with... 

Accumulation of agricultural chemicals in soils may lead to formation of nitrosamines. The herbicides atrazine and butralin were found to form nitrosamines only in the presence of high levels of nitrite. Active uptake of NDMA and NDEA by wheat and barley has been published however, no conclusive evidence has been reported80. 

All carbons are derived from either erythrose 4-phosphate (light purple) or phosphoenolpyruvate (pink). Note that the NAD+ required as a cofactor in step (3) is released unchanged it may be transiently reduced to NADH during the reaction, with formation of an oxidized reaction intermediate. Step (6) is competitively inhibited by glyphosate (COO—CH2—NH—CH2—PO ), the active ingredient in the widely used herbicide Roundup. The herbicide is relatively nontoxic to mammals, which lack this biosynthetic pathway. The chemical names quinate, shikimate, and chorismate are derived from the names of plants in which these intermediates have been found to accumulate. 

Herbicides are the biocides most likely to affect the metabolism of plants, including secondary metabolism [107]. The synthesis of hydroxyphenolics and anthocyanin in plants can be influenced by a variety of environmental and chemical stimuli. Some herbicides were found to raise the levels of these compounds in plants [108] whilst others had the opposite effect [109]. The products of secondary metabolism are controlled by enzymes, including PAL and chalcone isomerase (Cl), and several herbicides appear to intensify the activities of those enzymes involved in the accumulation of hydroxyphenolic compounds and anthocyanin biosynthesis in several plant species [109-111] whereas others depress this activity [112]. For example,... 

Research had confirmed that no parent simazine residues were found in treated com plants, and additional data on the dissipation pathway of simazine needed to be developed. Research also indicated that triazines interfered with the photosynthetic process on susceptible growing weeds, as evidenced by the appearance of chlorotic leaves. Steps were undertaken to elucidate simazine s dissipation pathway and herbicidal mode of action. In Basel, Dr. Gast (1958) showed that the accumulation of starch by common coleus (Coleus blumei Benth.) plants was inhibited from treatment with 2-chloro-4,6-bis-(alkyl-amino)-triazines due to the inhibition of sugar synthesis. At the same time, Moreland et al. (1958) found weed control activity could be reduced by supplying carbohydrates to the plants through their leaves and that simazine was a strong inhibitor of the Hill reaction in photosynthesis. Exer (1958) found that triazines inhibited the Hill reaction as strongly as urea of the CMU (monuron) type. 

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