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101.
THE dikaryophase of the wheat stem rust fungus, Puccinia graminis (Pers.) f. sp. tritici(Erikss. and E. Henn.), can now be grown on artificial medium1,2; but cultures of this organism initiated from heavy inocula of urediospores usually sporulate or stale after 2-4 weeks and the growth period cannot be appreciably prolonged by subculture onto fresh medium2,3. Scott and Maclean3, however, referred to the discovery of continuously subculturable isolates of P. graminis tritici. These were obtained by incubating urediospores on liquid nutrient medium, but Scott and Maclean offered no information which might explain the distinctive behaviour of the isolates. We have obtained lines of P. graminis tritici from race 126-Anz 6,7 (culture 70165) which will grow continuously on artificial medium. This communication describes how these lines were obtained and presents evidence that their mycelia are composed of diploid cells. 相似文献
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A phylogenetic survey using the polymerase chain reaction (PCR) has
identified four major P element subfamilies in the saltans and willistoni
species groups of Drosophila. One subfamily, containing about half of the
sequences studied, consists of elements that are very similar to the
canonical (and active) P element from D. melanogaster. Within this
subfamily, nucleotide sequence differentiation among different copies from
the same species and among elements from different species is relatively
low. This observation suggests that the canonical elements are relatively
recent additions to the genome or, less likely, are evolving slowly
relative to the other subfamilies. Elements belonging to the three
noncanonical lineages are distinct from the canonical elements and from one
another. Furthermore, there is considerably more sequence variation, on the
average, within the noncanonical subfamilies compared to the canonical
elements. Horizontal transfer and the coexistence of multiple,
independently evolving element subfamilies in the same genome may explain
the distribution of P elements in the saltans and willistoni species
groups. Such explanations are not mutually exclusive, and each may be
involved to varying degrees in the maintenance of P elements in natural
populations of Drosophila.
相似文献
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105.
Cytopathogenic agent resembling human salivary gland virus recovered from tissue cultures of human adenoids 总被引:43,自引:0,他引:43
106.
1. A protein component, fraction B, of lobster nerve extracts has been isolated and purified by differential ultracentrifugation and precipitation with zinc acetate. 2. Physicochemical data obtained from this protein and from fraction C are summarized. 3. Fraction B is present in lobster nerve extracts in higher concentration (relative to fraction A) than in blood. 4. A second component, fraction C, of sedimentation constant S(20) (o) = 13.2 has been isolated from lobster nerve extracts. 相似文献
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110.
The permanently eutrophic Sundays Estuary experiences recurrent harmful algal blooms (HABs) of Heterosigma akashiwo (Raphidophyceae). This study aimed to identify the environmental variables shaping phytoplankton community composition and succession patterns during a typical spring/summer harmful algal bloom (HAB) period. Monitoring of abiotic and phytoplankton variables was undertaken over the period of a month in 2016. Surface water salinity corresponding to mesohaline conditions (9 to 12) was a prerequisite for site selection. During the study, two HABs (>550 µg Chl a l?1) of H. akashiwo occurred, each lasting for approximately a week in duration. Analyses highlighted nutrient depletion (i.e. nitrate and phosphate concentrations) as the key constraint on bloom duration. When the density of H. akashiwo decreased, the community composition became more diverse with species belonging to Bacillariophyceae and Dinophyceae becoming more abundant; albeit to a lesser degree (<180 µg Chl a l?1). Dissolved oxygen shifted from super-saturated conditions (>14 mg l?1) during peak HAB conditions, to instances of bottom water oxygen depletion (2–4 mg l?1) during the decay phase. These findings highlight the potential severity of transforming a catchment from natural to one that is highly regulated by agricultural practices, while also emphasising the need for management intervention. 相似文献