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941.
942.
Pyrenophora tritici-repentis, the causal agent of tan spot disease of wheat, mediates disease by the production of host-selective toxins (HST). The known toxins are recognized in an ‘inverse’ gene-for-gene manner, where each is perceived by the product of a unique locus in the host and recognition leads to disease susceptibility. Given the importance of HSTs in disease development, we would predict that the loss of any of these major pathogenicity factors would result in reduced virulence and disease development. However, after either deletion of the gene encoding the HST ToxA or, reciprocally, heterologous expression of ToxA in a race that does not normally produce the toxin followed by inoculation of ToxA-sensitive and insensitive wheat cultivars, we demonstrate that ToxA symptom development can be epistatic to other HST-induced symptoms. ToxA epistasis on certain ToxA-sensitive wheat cultivars leads to genotype-specific increases in total leaf area affected by disease. These data indicate a complex interplay between host responses to HSTs in some genotypes and underscore the challenge of identifying additional HSTs whose activity may be masked by other toxins. Also, through mycelial staining, we acquire preliminary evidence that ToxA may provide additional benefits to fungal growth in planta in the absence of its cognate recognition partner in the host. 相似文献
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946.
BALB/c thymocytes were exposed to anti-μ serum in vitro, and both thymocytes and splenic T cells were exposed to anti-μ by long-term intensive treatment of intact animals. In all cases, the anti-μ-treated T cells could cooperate with splenocytes from nude mice in the in vitro immune response to sheep erythrocytes, indicating that cooperating T cells are not targets for immunosuppression by heterologous anti-μ antibodies. 相似文献
947.
During anemic episodes, goats and certain sheep replace hemoglobin A (HbA = α2β2A) with hemoglobin C (HbC = α2β2C). Rabbit serum directed against either purified sheep HbA or purified sheep HbC was prepared. Both types were used to test whether the two hemoglobins are found in the same cell during switching by an indirect fluorescent antibody assay.Unabsorbed antisheep HbA cross-reacted extensively with goat HbA but to a lesser extent with goat or sheep HbC. Similarly, unabsorbed antisheep HbC reacted with these antigens in the order: Sheep HbC > goat HbC > sheep HbA > goat HbA. Cross-absorption resulted in sera specific either for sheep and goat HbA or for sheep and goat HbC. The specificities were confirmed by indirect fluorescent antibody staining of sheep and goat erythrocytes containing either at least 99% HbA or at least 99% HbC.Smears of erythrocytes from sheep and goats in the process of switching were reacted with one of the absorbed sera then with fluorescein conjugated antirabbit immunoglobulin G. The sum of the fractions stained both by anti-HbA and by anti-HbC exceeded 100% during the switch. Most strikingly when HbA was replacing HbC, nearly all cells stained for HbC while more than half stained for HbA. Thus, the two hemoglobins are found in the same cell during switching. 相似文献
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949.
Kenneth Manning 《Journal of biochemical and biophysical methods》1981,5(4):189-202
A viscometric assay for the determination of carboxymethylcellulase is described. The method, which is developed from a direct theoretical approach, takes into account a kinetic energy correction and the non-Newtonian behavior of carboxymethylcellulose solutions. The enzymic hydrolysis of carboxymethylcellulose shows strong competitive inhibition by the products of the reaction and a method is presented for estimating the initial velocity of such reactions. A direct chemical determination of reducing end groups was used to confirm the validity of this approach. 相似文献
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