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131.
Stefan Falk Guy Samson Doug Bruce Norman P. A. Huner David E. Laudenbach 《Photosynthesis research》1995,45(1):51-60
Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43 apoprotein (designated isiA
–) and (ii) flavodoxin (designated isiB
–). The function of CP 43 was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA
– and isiB
– strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43 and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43 is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB
– strain grown under iron-deficient conditions, CP 43 was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (Fo) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.Abbreviations Chl
chlorophyll
- CP 43, CP 47 and CP 43
Chl a binding protein complexes of indicated molecular mass
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- Fm and Fm
fluorescence when all PS II reaction centers are dosed in dark- and light-acclimated cells, respectively
- Fo
fluorescence when all PS II reaction centers are open in dark acclimated cells
- Fv
variable fluorescence after dark acclimation (Fm–Fo) 相似文献
132.
Six cDNAs representing unique cold-induced sequences have been cloned from the hardy citrus relative Poncirus trifoliata. Among these, pBCORc115 and pBCORc119 were found to belong to the same gene family. Sequencing data indicated that pBCORc115 and pBCORc119 each contained an open reading frame, coding for a 19.8 kDa protein (COR19) and a smaller 11.4 kDa protein (COR11) respectively. Inspection of the deduced amino acid sequences revealed three large repeats in COR19, but only one was present in the COR11. Two elements: a Q-clustered tract and a K-rich motif were identified in each repeat. The K-rich motifs were similar to those of cotton D-11 and Group 2 LEA proteins. A Serine-cluster, a common feature in many Group 2 LEA-like proteins, was also found in these proteins, but it was in an unusual position at the carboxy-terminus. A bipartite motif of basic residues, similar to known nuclear targeting sequences, was also present in COR19 and COR11, suggesting that members of this protein family may have a nuclear targeting function. The expression of COR19 mRNA in response to cold acclimation, drought, flooding, and salinization was examined. COR19 expression in leaf tissue was induced in response to cold acclimation, but repressed during drought and flooding stress. 相似文献
133.
Stereognostic coordination chemistry 4 the design and synthesis of a selective uranyl ion complexant
A new approach to ligand design for the sequestration of metal-oxo cations has been called stereognostic coordination chemistry, in that the ligand incorporates a traditional Lewis base coordination to the metal center and a hydrogen bond donor to interact with the oxo group. This paper reports the synthesis of ligands that are more rigid and sterically predisposed to bind the targeted UO22+ cation. These are the tripod ligands tris-N,N′,N′′-[2-(2-carboxy-phenoxy)ethyl]-1,4,7-triazacyclononane bis-hydrochloride (ETAC · 2HCl) and tris-N,N′,N′′-[2-(2-carboxy-4-decyl-phenoxy)ethyl]-1,4,7-triazacyclononane tris-hydrochloride (DETAC · 3HCl), which chelate uranyl with a tris-carboxylate coordination sphere and provide a hydrogen bond donor through a protonated amine on the triazacyclononane macrocycle to interact with one uranyl oxo atom. Structural models predict that upon uranyl binding the hydrogen bond donor must point directly towards the oxo atom, enforcing a stereognostic interaction. Both ETAC and DETAC chelate the uranyl ion; DETAC is a powerful extractant and will quantitatively extract uranyl into an organic phase at pH 1.9 and above. The extraction coefficient is estimated to be 1014 in neutral aqueous conditions. Vibrational spectra of 18O labeled UO22+ have been used to probe the stereognostic coordination to uranyl utilizing hydrogen bonding. 相似文献
134.
135.
Hummel Herman Bogaards Roelof Bek Tatiana Polishchuk Lennard Amiard-Triquet Claude Bachelet Guy Desprez Michel Strelkov Peter Sukhotin Alex Naumov Andrei Dahle Salve Denisenko Stanislav Gantsevich Michael Sokolov Kirill Wolf Lein de 《Hydrobiologia》1997,355(1-3):127-138
The stress sensitivity, determined in copper exposureexperiments and in survival in air tests, and thegenetic structure, measured by means of isoenzymeelectrophoresis, were assessed in populations of theBaltic clam Macoma balthica (L.) from itssouthern to its northern distribution limit, in orderto test the hypotheses that near the distributionlimit the clams would be more stress sensitive andwould have a lower genetic variability. Thepopulations in west and north Europe show a stronggenetic resemblance. The populations in the sub-ArcticWhite Sea are genetically slightly different, and showa low stress sensitivity. The populations in theArctic Pechora Sea are genetically very distant fromthe other populations, and show the lowest stresssensitivity. Near the southern distribution limit, inagreement with the hypotheses, genetic variability islow and stress sensitivity high. On the other hand, incontrast to expectation, near the northerndistribution limit, in the populations of the PechoraSea, the genetic variability was higher, thus notreduced, and the stress sensitivity was low comparedto all other populations. Yet, it remains a questionif such is due to gradual physiologicalacclimatization (and ongoing differential selection)or to genetic adaptation. 相似文献
136.
Hall Robert D.; Riksen-Bruinsma Tjitske; Weyens Guy; Lefbvre Marc; Dunwell Jim M.; Tunen Arjen Van; Krens Frans A. 《Journal of experimental botany》1997,48(2):255-263
A highly-efficient protocol for the large-scale isolation ofguard cell protoplasts from sugar beet (Beta vulgaris L.) hasbeen developed. Optimization of conditions for culturing theseprotoplasts resulted in extensive cell division and colony formation,at frequencies exceeding 50%. Plants can subsequently be regeneratedfrom these guard cell-derived colonies. This provides definitiveconfirmation that, in sugar beet leaf protoplast populations,only guard cells are the source of totipotent protoplasts. Thesefindings are the outcome of a directed, non-empirical approachto overcoming plant cell recalcitrance which was initiated byexploiting computer-assisted microscopy to couple in vitro responseto cell origin. The results reaffirm the conclusion that, inplants, extreme degrees of cytodifferentiation need not entailterminal specialization. The responsive nature of this systemcan be ascribed to the unique use of cultures essentially comprisinga single in vivo cell type. A uniform model system has thusbeen created with potential for widespread application. Theirdistinct morphological (and mechanical) features make guardcells a valuable choice for studying various fundamental aspects,not only of stomatal physiology, but also of plant cell (de)differentiation,differential gene expression etc. Furthermore, an applied valuefor such a system can also be envisaged. Results indicate thatthese cells are highly amenable to genetic manipulation techniques.The importance of these observations to our understanding ofplant cell function and behaviour is discussed. Key words: Beta, guard cells, stomatal physiology, totipotency, transformation 相似文献
137.
Muriel Bost Mary Berkaw O. Wesley McBride Guy Chazot Philippe Arnaud 《Human genetics》1995,96(2):239-240
Using a probe isolated from a human liver cDNA library, polymorphisms were observed in the human ceruloplasmin gene with the enzymes PstI and MspI. The PstI polymorphism was frequent (allele frequencies, 0.46 and 0.54) whereas the polymorphisms found with MspI were rare. 相似文献
138.
Suzanne Demczuk Annie Lévy Muriel Aubry Marie-Françoise Croquette Nicole Philip Marguerite Prieur Ursula Sauer Patrice Bouvagnet Guy A. Rouleau Gilles Thomas Alain Aurias 《Human genetics》1995,96(1):9-13
We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a 2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin. 相似文献
139.
Specific absorption rates (SARs) were determined theoretically and experimentally for several spherical models of tissue exposed to electrical fields of TE101 mode in a rectangular cavity of 57.3 MHz resonant frequency. The approximate theoretical SAR can be calculated according to the Mie theory by superposition of four plane waves representing the fields excited in the cavity. The theoretical and thermographically determined SAR patterns in spheres with radii of 5, 7.5, and 10 cm and with conductivities of 0.1, 1, and 10 S/m were compared. For a sphere with radius less than 7.5 cm and conductivity less than 1 S/m, the SAR was quite uniform. When conductivity was increased to 10 S/m, the SAR patterns showed higher absorption in the periphery of the largest sphere (10-cm radius). These characteristics are important in evaluating the scaling technique of exposing a model of a human to very-high-frequency fields to obtain power absorption data in humans exposed to high-frequency or very-low-frequency fields. 相似文献
140.
Average specific absorption rates (SARs) for live rats exposed in 2,450-MHz circularly polarized waveguides were estimated from the total system loss determined from measurements using five power meters, and a correction factor representing actual SAR/apparent SAR. The actual SAR was measured by twin-well calorimetry and the apparent SAR by power meters. Values were obtained for carcasses of various body masses for five orientations. The average SAR with free movement in the cages changed less than threefold as the rats grew from 200 to 700 g. The ratio of peak to average SAR in the body was less than 3. These results indicate relatively constant energy disposition in rats exposed in the circularly polarized waveguide. 相似文献