Variation In Host Specificity Research Articles

MECHANISMS FAVOURING OUTBREEDING IN STRIGA HERMONTHICA [SCROPHULARIACEAE

SummarySelf‐incompatibility has been demonstrated in two samples of the parasitic flowering plant, Striga hermonthica, originating from Upper Volta and Sudan. Compatibility was determined by fluorescence microscopy of stigmatic preparations following controlled pollinations. Self incompatibility was associated with floral adaptations favouring pollination by long‐tongued insects such as butterflies. Outbreeding accounts for the variability of S. hermonthica, both in morphology and in host‐specificity. Genetic variation in host specificity imposes limits upon the effectiveness of the present methods of testing tropical cereals for resistance to S. hermonthica.

Changes in conformation and charge paralleling proteolytic activation of Newcastle disease virus glycoproteins

The hemagglutinin-neuraminidase and the fusion glycoprotein of strains Italien and Ulster of Newcastle disease virus were isolated by isoelectric focusing after solubilization with n-octylglucoside or other nondenaturing detergents. The isoelectric points of the glycoproteins varied depending on the virus strain; host-specific variations were not observed. When the precursor F 0 of the fusion protein of strain Ulster was converted by proteolytic cleavage into the complex F 1, 2, there was a shift in the isoelectric point from pH 6.3 to pH 5.0. When the precursor HN 0 of the same strain was cleaved to HN, its isoelectric point (pH 5.6) did not change. A shift from a more basic to a more acidic pH was also observed, when the isoelectric points of F 0 and F 1, 2 were analyzed under denaturing conditions. These observations are compatible with the concept that F 1 and F 2 are linked in the precursor by a basic intervening sequence that is eliminated in the cleavage reaction. Circular dichroism spectra of the isolated glycoproteins have been determined. The spectra obtained from glycoprotein F 1, 2 of strain Italien and of strain Ulster were similar, but there were strain-specific differences with glycoprotein HN. With the hemagglutinin-neuraminidase and the fusion protein of strain Ulster, precursors and cleavage products showed different spectra. This indicates that proteolytic activation of both glycoproteins is paralleled by a conformational change.

Sylvatic plague studies in southeast New Mexico. I. Flea-host relationships from six years' study.

From March 1967 to November 1972, 6330 mammals of 11 species were live-trapped in mesquite-grassland and giant sacaton grass habitat in Chaves County, southeastern New Mexico. These mammals yielded 38,549 fleas of 18 species. Quantitative data are presented on relative abundance, seasonal occurrence, and host preference of the 18 flea species. The most abundant flea collected during the study was Meringis rectus . A total of 15,765 fleas of this species was collected from 11 mammal species. The least abundant flea was Pulex simulans , with only 8 specimens collected from 2 mammal species. The number of flea species recovered from a given host species ranged from 15, collected from Sigmodon hispidus , to 2, from Perognathus flavus . All but 3 of the 18 flea species were collected in highest numbers during the fall, winter, and spring months. A considerable amount of variation in host specificity was exhibited among the 18 flea species.

Lysogeny in Rhizobium Leguminosarum and Rh. Trifolii

Seven lysogenic strains-three of Rh. legumino8urum and four of Rh. trifoliiwere identified among a total of 54 strains from these two species and Rh. phaseoli. The Rh.leguminosarum strains may be multiply lysogenic; two of them also produce lethal agents resembling bacteriocins in their effect. Lysogeny was confumed by standard criteria of ultraviolet light inducibility, self.immunity, and reductive ability. Lysogenic conversion involving symbiotic characteristics was not observed. A minimum of six different temperate phages and two clear-plaque-forming variant phages were identified. The host range includes strains of the above three rhizobial species, but not of Rh. melilotii. Variation in host specificity of some phages following host passage is under investigation.

A host-specific variation affecting relative frequency of transformation of two markers in pneumococcus

Two different strains of pneumococcus show a markedly different transformation frequency for a given genetic marker ( str) in a transforming preparation while showing identical frequencies for another genetic marker ( ery 2) in the same transforming preparation. It was concluded that the frequency of the transformation to streptomycin resistance was consistently lowered in one receptor strain. The kinetics of expression of the str marker in the affected host indicates the abrupt cessation of an otherwise normal expression of the str transformants between 40 to 50 minutes after the initial exposure to DNA, whereas in the unaffected host expression of str transformants continues for at least another 30 minutes. From the initial rate of expression of the str markers on the affected and the unaffected hosts, it was concluded that the number of incorporated transformants was identical for both hosts, and that some post-incorporation elimination of determinants was responsible for the different relative frequency on Rz. The transformation of the ability to cause a depressed transfer of the str agent has been studied, and its association with and separability from the str marker revealed. The presence of the depressor factor has been shown to greatly influence the recovery of the str marker from UV-irradiated DNA-preparations. The nature of the factor responsible for the depression of the str marker is discussed.