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Nitrification is a key stage in the nitrogen cycle; it enables the transformation of nitrogen into an oxidized, inorganic state. The availability of nitrates produced by this process often limits primary productivity and is an important determinant in plant community ecology and biodiversity. Chemoautotrophic prokaryotes are recognized as the main facilitators of this process, although heterotrophic nitrification by fungi may be significant under certain conditions. However, there has been neither biochemical nor ecological evidence to support nitrification by photoautotrophic plants. Here we show how certain legumes that accumulate the toxin, 3-nitropropionic acid, generate oxidized inorganic nitrogen in their shoots, which is returned to the soil in their litter. In nitrogen-fixing populations this 'new' nitrate and nitrite can be derived from the assimilation of nitrogen gas. Normally, the transformation of elemental nitrogen from the atmosphere into a fixed oxidized form (as nitrate) is represented in the nitrogen cycle as a multiphasic process involving several different organisms. We show how this can occur in a single photoautotrophic organism, representing a previously undescribed feature of this biogeochemical cycle. 相似文献
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Arash Khakzadshahandashti Mohammad Reza Rahimipour Kourosh Shirvani Mansour Razavi 《北京科技大学学报》2019,(2)
The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding(EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ′ liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ′ precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area. 相似文献
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Abdel Halim Harrath Ronald Sluys Lamjed Mansour Guy Lekeufack Folefack Waleed Aldahmash Saleh Alwasel 《Journal of Natural History》2019,53(5-6):253-271
The paper describes two new Dugesia species collected from the rivers Messassi and Ntsetsensooh in Cameroon, representing the first planarian flatworms documented from this country. Based on morphological data, the new species Dugesia bijuga Harrath & Sluys, sp. nov. is characterized mainly by the presence of two diaphragms, a barrel-shaped penis that is traversed by numerous ducts of penis glands and is provided with a short nozzle, and the presence of two atrial folds. The other new species, Dugesia pustulata Harrath & Sluys, sp. nov., is characterized mainly by absence of a penis bulb, presence of a large, elongated and weakly muscular seminal vesicle, and by the ventroposterior section of the bursal canal being thrown into distinct folds. The phylogenetic position of the two new species was determined through a molecular phylogenetic tree, based on a mitochondrial and a nuclear gene, including species from the major geographical range of distribution of the genus Dugesia. The phylogenetic tree revealed that the Cameroon lineage does not constitute a monophyletic group with the other Afrotropical species; it also showed that the African continent may house a great diversity of Dugesia species that still remains to be discovered.
urn:lsid:zoobank.org:pub:007441A5-F037-4950-9F5B-AD6ED12A40ED 相似文献
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Platinum compounds: a new class of potent antitumour agents 总被引:38,自引:0,他引:38
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Mutations in RNF135, a gene within the NF1 microdeletion region, cause phenotypic abnormalities including overgrowth 总被引:2,自引:0,他引:2
Douglas J Cilliers D Coleman K Tatton-Brown K Barker K Bernhard B Burn J Huson S Josifova D Lacombe D Malik M Mansour S Reid E Cormier-Daire V Cole T;Childhood Overgrowth Collaboration Rahman N 《Nature genetics》2007,39(8):963-965
17q11 microdeletions that encompass NF1 cause 5%-10% of cases of neurofibromatosis type 1, and individuals with microdeletions are typically taller than individuals with intragenic NF1 mutations, suggesting that deletion of a neighboring gene might promote human growth. We identified mutations in RNF135, which is within the NF1 microdeletion region, in six families characterized by overgrowth, learning disability, dysmorphic features and variable additional features. These data identify RNF135 as causative of a new overgrowth syndrome and demonstrate that RNF135 haploinsufficiency contributes to the phenotype of NF1 microdeletion cases. 相似文献
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Zusammenfassung Subletale Dosen einiger inizierter Antimetaboliten, Pflanzenwuchsstoffe und Juvenilhor monimitatoren beschleunigen oder verlangsamen und reduzieren das Wachstum der Raupen vonAgrotis ypsilon. Alar löste in einigen Raupen eine Überzählige Larvenhäutung aus und es ergaben sich Riesenraupen. 相似文献
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The expression of immunodeficiency in patients with specific purine enzyme defects indicates a crucial role of the purine salvage pathway in the acquisition and expression of normal immune function. One current hypothesis links the failure of normal lymphocyte development in these diseases to the accumulation of deoxynucleotide triphosphates. In our studies of human in vitro IgM responses, we observed that antigen-induced T-suppressor cell activity was abrogated in the presence of micromolar concentrations of deoxyguanosine (dGuo). In contrast, more than 1,000-fold higher resistance to dGuo was found for both noin-proliferative T-helper cell activity and the differentiation and proliferation of the precursor B lymphocytes for direct haemolytic plaque forming cells (PFC). To determine whether these observations could have in vivo relevance, we monitored the generation of murine T-suppressor cells, capable of abrogating a primary IgM response. It was found that dGuo (but not guanosine) selectively inhibited the in vivo development of T-suppressor cells. 相似文献