Resistance-susceptibility studies using

Resistance - Susceptibility Studies Using Natural Budworm Densities and Defoliation... 

No one knows how many crop varieties are affected adversely by air pollution beyond the few which have been studied. Thus, it is important that surveys continue to be made of the susceptibility of useful plant species, particularly those grown in areas of high air pollution incidence and in areas of potentially high incidence. These surveys should include all the major air toxicants known to cause injury to plants in each area. The genetic state of each crop must be assessed, and, in those crops which are uniformly susceptible, it will be necessary to screen noncommercial materials for resistance, possibly including wild relatives. Appropriate breeding programs can then be started. 

The so-called resistant strains, however, show a different response to mercury exposure. These resistant strains also show an increase in MHC expression molecules on B-cells, but this response is extremely short-lived, and increases in serum IgE were not observed (Dubey et al. 1991a Prouvost-Danon et al. 1981). The difference in the responses of the so-called resistant and susceptible strains may be found in the activation of Thl cells and the increase in secretion of -interferon by the Thl cells of resistant animals (van der Meide et al. 1993). The susceptible strains do not show an increase in -interferon production with mercury exposure. Because -interferon inhibits the proliferation of Th2 cells, the absence of this response in the susceptible strains may allow the Th2 cell-stimulated production of autoantibodies to occur, whereas in the resistant strains the production of antibodies is curtailed. Thus, differences in the activation of Thl versus Th2 cells may underlie the differences in susceptibility of various individuals. Studies using in-bred strains of mice and rats have determined that the susceptibility to the different immune reactions is governed by both MHC genes as well as other genes (Aten et al. 

Before doing this, however, it is useful to briefly consider the biosynthesis of anacardic acids. It is believed that anacardic acids are synthesized from long chain fatty acids via a modification of the methyl salicylate synthetase scheme (11. 12). In effect a fatty acid, such as palmitate (Cie) is elongated by six carbons by the addition of three acetate units in a series of condensation and dehydration steps, followed by ring closure and aromatization to form a C22 saturated anacardic acid (5. 10. U ). Similarly, margaric acid (C17) is synthesized to a C23 saturated anacardic acid. A comparative study on the biosynthesis of anacardic acids in resistant and susceptible plants, using fatty acid precursors will be the subject of a separate publication. 

Potentiodynamic polarization measurements are quite appropriate for determination of the pitting susceptibility of aluminum coatings, and/or the corrosion current density/ corrosion rate of coated steel products in general. ASTM G 102, Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements, describes the calculation of corrosion rates and other information from electrochemical measurements. Another example of the use of DC electrochemical methods to examine the corrosion performance of coated sheet materials is a study by D. A. Jones et al. [48]. The study used polarization resistance measurements to examine the mechanism of steel and coated sheet degradation under conditions of alternate immersion. Jones compared the polarization resistance of samples of low-carbon steel, unpainted galvanized, aluminum-coated, and Zn-Ni alloy coated steel during continuous immersion and alternate immersion. Alternate immersion cyclic exposure produced a thick oxide that led to significant underfilm attack. Jones found that phosphate pretreatment tends to increase the resistance of these materials to underfilm attack. This study is an excellent example of the way electrochemical measurements can be used as a complement to other techniques to elucidate mechanistic information. 

Streicher has studied various stainless steels, Inconels, Hastelloys and pure metals such as Ni, Mo, Ti, Ta and Nb using an artificial crevice (Fig. 1.49c to e) that gives rise to three different types of crevice conditions. In order to accelerate attack a 10% FeClj solution (pH 1-6) at 50°C was used and attack was found to occur within 24 h on all susceptible alloys, whereas it could take up to 4 months when the surface was free from a crevice. A stainless steel (SP-2 Fe-18Cr-10Ni-2-5Mo-2-5Si) was found to be most resistant to attack, whereas all other stainless steels (Including the molybdenum-containing alloys) failed. 

Although there has been substantial success using IFN for the treatment of some cancels, until this point, the great majority of tumors are resistant or show an initial moderate response soon followed by disease progression under treatment. One likely reason for resistance is the progredient loss of susceptibility to IFN, which may be caused by downregulation of IFN receptors or perturbation of intracellular DFN-signaling pathways, a phenomenon also known from in vitro studies. 

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