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51.
The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention
in recent years. However, insufficient information exists on the coordination of transpiration and CO2 uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration
(E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and
first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas
exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and
fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed
for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf
age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial
leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO2 mmol−1 H2O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in
stomatal conductance (gs·H2O) since decreases in gs·H2O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along
the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these
findings are presented in relation to light competition within the plant canopy during development. 相似文献
52.
James M. Chen Grace Lee Paul W. Brandt-Rauf Randall B. Murphy Shalom Rackovsky Matthew R. Pincus 《Journal of Protein Chemistry》1990,9(5):543-547
The predicted conformation and position of the central transforming region (residues 55–67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1–166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an -helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data. 相似文献
53.
Increased frequency of 6-thioguanine-resistant peripheral blood lymphocytes in Werner syndrome patients 总被引:1,自引:1,他引:0
Ken-ichiro Fukuchi Kiyoji Tanaka Yuichi Kumahara Kazuo Marumo Matthew B. Pride George M. Martin Raymond J. Monnat Jr. 《Human genetics》1990,84(3):249-252
Summary The frequency of spontaneous 6-thioguanine (TG)-resistant peripheral blood lymphocytes in five unrelated Werner syndrome (WS) patients was determined using an autoradiographic labeling assay. The average frequency of TG-resistant lymphocytes was eightfold higher in WS patients than in sex- and age-matched normal control donors. This finding and previous identification of increased spontaneous chromosomal rearrangements and deletions in WS cells or cell lines suggest that WS is a human genomic instability or mutator syndrome. 相似文献
54.
55.
Dr. Matthew D. Collins Reiner M. Kroppenstedt Jin Támaoka Kazuo Komagata Takeshi Kinoshita 《Current microbiology》1988,17(5):275-279
The structures of the tetrahydrogenated menaquinones fromActinomadura angiospora, Faenia rectivirgula, andSaccharothrix australiensis were determined by mass spectrometry and proton nuclear magnetic resonance spectrometry. The positions of saturation of the tetrahydrogenated menaquinones fromFaenia rectivirgula andSaccharothrix australiensis were units II plus III (counting from the ring system), whereas that ofActinomadura angiospora had units III and VIII hydrogenated. The tetrahydrogenated menaquinones fromFaenia rectivirgula andSaccharothrix australiensis are similar to those characterized from other Gram-positive taxa to date, whereas that fromActinomadura angiospora represents a hitherto unknown isomer. 相似文献
56.
Chemotaxonomic studies were performed on some heterofermentative lactobacilli of uncertain taxonomic position. Two strains from beer and six strains from a variety of habitats were found to be distinct from each other and all other Lactobacillus species examined on the basis of DNA-DNA hybridizations and warrant new species for which the names L. malefermentans and L. parabuchneri , respectively, are proposed. 相似文献
57.
Thomas L. Pazdernik Matthew Layton Stanley R. Nelson Fred E. Samson 《Neurochemical research》1992,17(1):11-21
This overview presents data showing that glucose use increases and that excitatory amino acids (i.e., glutamate, aspartate), taurine and ascorbate increase in the extracellular fluid during seizures. During the cellular hyperactive state taurine appears to serve as an osmoregulator and ascorbate may serve as either an antioxidant or as a pro-oxidant. Finally, a unifying hypothesis is given for seizure-induced brain damage. This unifying hypothesis states that during seizures there is a release of excitatory amino acids which act on glutamatergic receptors, increasing neuronal activity and thereby increasing glucose use. This hyperactivity of cells causes an influx, of calcium (i.e. calcium stress) and water movements (i.e., osmotic stress) into the cells that culminate in brain damage mediated by reactive oxygen species.Special issue dedicated to Dr. Frederick E. Samson 相似文献
58.
A previously undescribed, H2-oxidizing CO2-reducing acetogenic bacterium was isolated from gut contents of the wood-feeding termite, Pterotermes occidentis. Cells of representative strain APO-1 were strictly anaerobic, Gram-negative, endospore-forming motile rods which measured 0.30–0.40×6–60 m. Cells were catalase positive, oxidase negative, and had 51.5 mol percent G+C in their DNA. Optimum conditions for growth on H2+CO2 were at 30–33°C and pH (initial) 7.8, and under these conditions cells formed acetate according to the equation: 4 H2+2 CO2CH3COOH+2 H2O. Other energy sources supporting good growth of strain APO-1 included glucose, ribose, and various organic acids. Acetate and butyrate were major fermentation products from most organic compounds tested, however propionate, succinate, and 1,2-propanediol were also formed from some substrates. Based on comparative analysis of 16S rRNA nucleotide sequences, strain APO-1 was related to, but distinct from, members of the genus Sporomusa. Moreover, physiological and morphological differences between strain APO-1 and the six known species of Sporomusa were significant. Consequently, it is proposed herewith that a new genus, Acetonema, be established with strain APO-1 as the type strain of the new species, Acetonema longum. A. longum may contribute to the nutrition of P. occidentis by forming acetate, propionate and butyrate, compounds which are important carbon and energy sources for termites. 相似文献
59.
Clostridium mayombei sp. nov., a previously undescribed H2-oxidizing CO2-reducing acetogenic bacterium, was isolated from gut contents of the African soilfeeding termite, Cubitermes speciosus. Cells were anaerobic, Gram positive, catalase and oxidase negative, endospore-forming motile rods which measured 1×2 – 6 m and which had a DNA base composition of 25.6 mol% G+C (strain SFC-5). Optimum conditions for growth on H2+CO2 were at 33°C and pH 7.3, and under these conditions cells produced acetate according to the equation: 4 H2+2 CO2CH3COOH+2 H2O. Other substrates supporting good growth included carbohydrates (e.g. glucose, xylose, starch), sugar alcohols, and organic and amino acids, and with these substrates acetate was almost always the principle fermentation product. Comparative analysis of 16S rRNA nucleotide sequences confirmed that C. mayombei was closely related to various members of the genus Clostridium. However, morphological and physiological differences between C. mayombei and other homoacetogenic clostridia were deemed significant enough to warrant creation of a new taxon. Results are discussed in light of the diversity of H2/CO2 acetogens recently isolated from various termites, and in terms of the relative importance of H2/CO2 acetogenesis to termite nutrition. 相似文献
60.
The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge. 相似文献