Herbicidal damage

Cell potential, 9 607-609 standard, 75 750 Cell Saver, 3 719 Cells, encapsulation of, 76 454 Cell sorting, microfluidics in, 26 971-972 Cell-specific dendritic carriers, 26 797 Cell targeting, dendrimers in, 26 797-798 Cell thermo stating, 73 426 Cellular components inducers, herbicide damage to, 73 297-298 Cellular damage, in aging, 2 810 Cellular diseases, yeast as a model for, 26 496-497... 

These herbicides damage epithelial tissues, e.g., cornea, nails, skin, kidney, liver and linings of the QX and respiratory tracts. 

These mutants demonstrate that glutamine synthetase is a potential target for herbicidal compounds and they indicate that photosynthetic tissue is most vulnerable for herbicidal damage caused by GS inhibitors. 

Owing to the high substrate affinity of both enzymes, trace amounts of the proteins are sufficient to protect the transgenic plants from herbicidal damage. Even if less than 0.1% of the total protein consists of Bar or Pat protein, the respective plants efficiently acetylate phosphinothricin quantitatively when it enters the plant cells. These plants do not show any signs of GS inhibition even after application of high doses of glufosinate, which exceed the field application rate 5-10-... 

In plants treated with these herbicides, damage is light dependent and closely correlated with the level of PPIX that accumulates. PPIX accumulation is apparently largely extraplastidic. Treatment with the porphyrin precursor 5-aminolevulinic acid (ALA), in combination with the heme and chlorophyll pathway inhibitor 2,2 -dypyridyl (DP), results in the accumulation of toxic levels of primarily Mg-PPIX monomethyl ester. DP deregulates porphyrin synthesis and ALA provides additional substrate. DP and other chlorophyll synthesis modulators in combination with ALA can increase the selectivity as well as enhance the efficacy of ALA as a herbicide. Exogenously applied porphyrins are far less effective as herbicides than treatment with compounds that cause plants to accumulate their own porphyrins. 

Table I. Effects of ALA and DP, alone or in combination, on porphyrin accumulation and herbicidal damage. Cucumber seedlings (6-day-old) were assayed for porphyrins after being sprayed with the herbicides and incubated in darkness for 17 h. Herbicidal damage was assessed 10 days after porphyrins were assayed and during which they were exposed to greenhouse light conditions.

Others have found little correlation between the herbicidal effects and the amount of PPIX accumulated by Protox-inhibiting herbicides (50, 64). In cucumber (Fig. 4), pigweed, and velvetleaf, we found a strong correlation between the amount of PPIX accumulated in response to acifluorfen and the amount of ensuing herbicidal damage (41). Also, there was an excellent correlation between the PPIX and the resulting herbicidal damage caused by a variety of diphenyl ether and oxadiazole herbicides (41). 

Some laboratories (64 M) have found PChlide to be the primary porphyrin to accumulate in diphenyl ether-treated tissues. In our green cucumber cotyledon disc system, we have found only PPIX levels to be increased by these herbicides (67), however, in intact cucumber seedlings (Fig. 5) and tentoxin-affected cucumber cotyledon discs ( S) we found diphenyl ether-enhanced PChlide levels. PPIX levels accumulate to many (as much as several hundred) times the control levels in herbicide-treated tissues, whereas the maximum PChlide accumulation is only four-fold that of the control. Since the metabolic block is at Protox, there is no inhibition of conversion of PChlide to Chi after exposure to light. Therefore, it seems unlikely that PChlide plays a significant part in the mechanism of action of these herbicides. Indeed, of the Chi precursors assayed, only PPIX significantly correlated with herbicidal damage caused by a several different acifluorfen/DP/ALA treatment combinations ( 7). No significant correlations were found with accumulated PChlide,... 

Agricultural Products. Pesticides are frequendy appHed as emulsiftable concentrates. The active insecticide or herbicide is dissolved in a hydrocarbon solvent which also contains an emulsifier. Hydrocarbon solvent selection is critical for this appHcation. It can seriously impact the efficacy of the formulation. The solvent should have adequate solvency for the pesticide, promote good dispersion when diluted with water, and have a dash point high enough to minimise dammabiUty ha2ards. When used in herbicide formulas, low solvent phytotoxicity is important to avoid crop damage. Hydrocarbon solvents used in post-harvest appHcation require special testing to ensure that polycycHc aromatics are absent. 

TCDD is the most potent inducer of chloracne. This has been well known since the accident in Seveso, Italy, in 1976 in which large amounts of TCDD were distributed in the environment subsequent to an explosion in a factory that produced a chlorophenoxy herbicide, 2,4,5-T. TCDD is an impurity produced during the production of 2,4,5-T. The most common long-term effect of TCDD exposure was chloracne. Exposed individuals also suffered increased excretion of porphyrins, hyper-pigmentation, central nervous system effects, and liver damage and increased risk of cancer was a long-term consequence of the exposure. In addition to TCDD, polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans, and polychloronaphthalens cause chloracne as well as other effects typical of TCDD. 7i... 

One problem that has arisen with the use of herbicides in agriculture is spray or vapor drift. When fine spray droplets are released, especially if applied aerially, they may be deposited beyond the target area due to air movements to cause damage there. In the first place, this is a question of application technique. Herbicides, like other pesticides, should not be applied as sprays under windy conditions. In most... 

After introducing recommended amounts of terbutrin and chlortoluron, wheat suffered more seriously from downy mildew. Monolinuron and simazin affected winter wheat similarly. Herbicides such as 2,4-MCPA, ioxynil, dicamba, and several others increased the amount of root rot damage to winter wheat on average by 60% when compared with the control crop. Treating grain crops using... 

Resistant weeds may appear and spread with the intensive use of herbicides these are plants whose root systems are found in the deep layers of the soil, and are damaged by herbicides to a lesser degree [3]. Thus, as a result of the intensive use of pesticides, the number of target species increases rather than decreases. 

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