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31.
32.
Photo-oxidative damage in the ripening tomato fruit: Protective role of superoxide dismutase 总被引:2,自引:0,他引:2
Factors relating to photo-oxidative damage in tomatoes were investigated during maturation of the fruit and upon induction of sunscald. Superoxide dismutase (SOD) activity passed through a minimum at the mature-green and breaker stages of ripening and availability of zinc and copper did not appear to be a limiting factor in the synthesis of the enzyme. Iron levels were maximal and total carotenoid concentrations were lowest during the same mature-green and breaker stages of maturation, while chlorophyll was starting to decrease but was still present in large amounts. Peroxidase activity decreased steadily during ripening. Artificial induction of tolerance to photodynamic damage by controlled heat treatment was accompanied by an increase in SOD activity, while carotenoid levels and peroxidase activity did not change. These findings support the thesis that the previously reported susceptibility of tomatoes to photodynamic damage, i.e. sunscald, during the mature-green and breaker stages of maturation is related to enhanced formation of superoxide ions, at a time when chloroplast structure begins to break down. SOD, by scavenging the superoxide, appears to supplement the protective action of carotenoids against photo-oxidative injury. 相似文献
33.
Barbara Tillmann Pierre Jolic?ur Masami Ishihara Nathalie Gosselin Olivier Bertrand Yves Rossetti Isabelle Peretz 《PloS one》2010,5(4)
Congenital amusia is a neurogenetic disorder of music processing that is currently ascribed to a deficit in pitch processing. A recent study challenges this view and claims the disorder might arise as a consequence of a general spatial-processing deficit. Here, we assessed spatial processing abilities in two independent samples of individuals with congenital amusia by using line bisection tasks (Experiment 1) and a mental rotation task (Experiment 2). Both amusics and controls showed the classical spatial effects on bisection performance and on mental rotation performance, and amusics and controls did not differ from each other. These results indicate that the neurocognitive impairment of congenital amusia does not affect the processing of space. 相似文献
34.
Christophe Piscart Alain Manach Gordon H. Copp Pierre Marmonier 《Journal of Biogeography》2007,34(3):524-533
Aim To assess temporal changes in gammarid distribution in Brittany and microhabitat-use overlap between the endangered endemic Gammarus duebeni celticus Stock & Pinkster, 1970 , the expanding natives G. pulex (Linnaeus, 1758) and Echinogammarus berilloni (Catta, 1878), and the introduced G. tigrinus Sexton, 1939.
Location Brittany and adjacent regions in western France.
Methods The spatial and temporal patterns in distribution of gammarids at the scale of Brittany were studied using 351 sites. Longitudinal distributions (from the source to the estuary of the river) and microhabitat-use (substratum type and water velocity) were also considered in selected rivers.
Results At the regional scale, all species occurred together less often than expected statistically, with significant deviations from expected for G. pulex vs. both G. duebeni celticus and G. tigrinus , and for E. berilloni vs. both G. duebeni celticus and G. tigrinus . However, at the microhabitat scale, E. berilloni occurred significantly more often than expected with the endemic G. duebeni celticus , and this appears to be due to similar substratum and water velocity preferences, although at both the regional and microhabitat scales E. berilloni prefers wider streams than G. duebeni celticus . This study reveals a decline in the endangered G. duebeni celticus since 1970.
Main conclusions The longitudinal and local distributions of G. duebeni celticus , and the higher-than-expected co-occurrence of the species with G. pulex , suggest that the decline of the endemic species may be due to changes in the environment and/or interference from native G. pulex , which is expanding its range in Brittany. The results are discussed as regards to the consequences for regional biodiversity. 相似文献
Location Brittany and adjacent regions in western France.
Methods The spatial and temporal patterns in distribution of gammarids at the scale of Brittany were studied using 351 sites. Longitudinal distributions (from the source to the estuary of the river) and microhabitat-use (substratum type and water velocity) were also considered in selected rivers.
Results At the regional scale, all species occurred together less often than expected statistically, with significant deviations from expected for G. pulex vs. both G. duebeni celticus and G. tigrinus , and for E. berilloni vs. both G. duebeni celticus and G. tigrinus . However, at the microhabitat scale, E. berilloni occurred significantly more often than expected with the endemic G. duebeni celticus , and this appears to be due to similar substratum and water velocity preferences, although at both the regional and microhabitat scales E. berilloni prefers wider streams than G. duebeni celticus . This study reveals a decline in the endangered G. duebeni celticus since 1970.
Main conclusions The longitudinal and local distributions of G. duebeni celticus , and the higher-than-expected co-occurrence of the species with G. pulex , suggest that the decline of the endemic species may be due to changes in the environment and/or interference from native G. pulex , which is expanding its range in Brittany. The results are discussed as regards to the consequences for regional biodiversity. 相似文献
35.
The photoacoustic (PA) characteristics (energy storage and heat dissipation) of photosystem II (PSII) core-enriched particles from barley were studied (i) in conditions where there was electron flow, i.e., in the presence of a combination of the electron acceptor K3 Fe (CN)6, referred to as FeCN, and the electron donor diphenylcarbazide (DPC), and (ii) in conditions where electron flow was suppressed, i.e., in the absence of FeCN and DPC. The experimental data show that a decrease of heat dissipation with a minimum at 540 nm can be interpreted as energy storage resulting from the presence of pheophytin (Pheo) in the PSII particles. On account of the capability of the PA method to measure the energy absorbed by the chromophores which is converted to heat, it is suggested that the PA detection of Pheo present in the PSII complex will permit to clarify the function of processes involving non-radiative relaxation of excited states in P680-Pheo-QA interactions.Abbreviations -Car
-Carotene
- Chl
Chlorophyll
- DPC
Diphenylcarbazide
- EPR
Electron Paramagnetic Resonance
- FeCN
potassium ferricyanide
- HEPES
N-2-hydroxyethylenepiperazine-N-2-ethanesulfonate
- P680
reaction center of PSII
- PA
Photoacoustic
- Pheo
pheophytin
- PSI
photosystem I
- PSII
photosystem II
- QA
primary electron acceptor of PSII 相似文献
36.
Ahmed Lebrihi Pierre Germain Gérard Lefebvre 《Applied microbiology and biotechnology》1987,26(2):130-135
Summary Production of cephamycin and clavulanic acid by Streptomyces clavuligerus is controlled by the phosphate concentration. Phosphate represses the biosynthesis of cephamycin synthetase, expandase and clavulanic acid synthetase. In the presence of 2 mM phosphate, the specific activities of expandase, cephamycin synthetase and clavulanic acid synthetase were higher than in the presence of 75 mM phosphate. The specific activity of cephamycin synthetase is maximal with an initial phosphate concentration of 10 mM, whereas the specific activity of expandase is maximal with 1 mM phosphate. A correlation between cephamycin synthetase specific activity and expandase specific activity was established at phosphate concentrations higher than 10 mM. This shows that the expandase is an important enzyme in the mechanism by which the phosphate concentration affects the biosynthesis of cephamycin. 相似文献
37.
The mechanism of melibiose symport by the melibiose permease of Escherichia coli was studied by looking at the modifications of the facilitated diffusion properties of the permease which arise upon substitution of the coupled cations (H+, Na+, or Li+). Kinetic analysis of melibiose influx and efflux down a concentration gradient, exchange at equilibrium, and counterflow were examined in de-energized membrane vesicles resuspended in media allowing melibiose to be co-transported with either H+, Na+, or Li+. The data show that the maximal rates of melibiose efflux coupled to either H+, Na+, or Li+ are between 10 and 40 times faster than the corresponding influxes. This suggests that the permease functions asymmetrically. Cross-comparison between the rates of net [3H]melibiose entry during the influx reactions coupled to either cation and corresponding unidirectional sugar inflow during exchange and counterflow reactions leads to the conclusions that: 1) the step involving release of the co-substrates from the permease on the inner surface of the membrane is sequenced (sugar first and then coupled cation); 2) this step is rate determining for cycling of the permease. The Na+-melibiose passive flux data indicate in particular that release of Na+ ions rather than release of sugar into the intravesicular space is the slowest step during permease cycling. This property would hamper net passive Na+-melibiose influx but should allow exchange of sugar without concomitant exchange of the coupled cation. Finally, evidence is provided suggesting that the relative rates of release of the two co-substrates from the permease on the inner membrane surface varied considerably in relation to the identity of the coupled cation. 相似文献
38.
Axonal Transport Characteristics of Gangliosides in Sensory Axons of Rat Sciatic Nerve 总被引:2,自引:2,他引:0
G. Jean Harry Jeffry F. Goodrum Arrel D. Toews† Pierre Morell† 《Journal of neurochemistry》1987,48(5):1529-1536
The distribution of axonally transported gangliosides and glycoproteins along the sciatic nerve was examined from 3 h to 4 weeks following injection of[3H]glucosamine into the fifth lumbar dorsal root ganglion of adult rats. Incorporation of labeled precursor into these glycoconjugates reached a maximal level in the ganglion within 6 h. Outflow patterns of radioactivity for glycoproteins showed a well-defined crest with a transport rate of approximately 330 mm/day. In contrast, the crest of transported gangliosides was continuously attenuated, implying a significant deposition along the axon, and an alternative method of calculating velocity was required. Analysis of accumulation of labeled material at double ligatures demonstrated both anterograde and retrograde transport of glycoproteins and gangliosides and allowed for the calculation of an anterograde transport rate of about 270 mm/day for each. Additional evidence of ganglioside transport is provided in that the TLC pattern of transported radioactive gangliosides accumulating at a ligature is significantly different from the pattern seen in the dorsal root ganglion or following intraneural administration of the labeled precursor. These data indicate that gangliosides are transported at the same rapid rate as glycoproteins but are subject to a more extensive exchange with stationary material than are glycoproteins. 相似文献
39.
Dinucleoside tetraphosphate variations in cultured tumor cells during their cell cycle and growth 总被引:3,自引:0,他引:3
Gilbert Moris Denise Meyer Georges Orfanoudakis Nicole Befort Jean-Pierre Ebel Pierre Remy 《Biochimie》1987,69(11-12):1217-1225
Asynchronous and synchronized cultures of A549 and HTC cells were used to detect possible, cell cycle or cell density specific variations in the intracellular pools of dinucleoside tetraphosphates (Ap4X). No important variations of the nucleotide pools were observed during cell growth. When HTC cells were released from mitotic arrest, a decrease by a factor of N3 Ap4X and ATP levels was observed when the cells entered the G1 phase. This decrease is essentially due to cell doubling. When A549 cells were released from an arrest at the G1/S boundary, the nucleotide pool size increased slightly during the G2 phase just before mitosis. This result is in agreement with both earlier data from our laboratory and the observed decrease in Ap4X pool after release from mitotic-arrested HTC cells. These results suggest that the Ap4X and ATP pools are only subjected to very small variations during the cell cycle, essentially in the G2 phase and after mitosis. 相似文献
40.
Human elongation factor 1α: a polymorphic and conserved multigene family with multiple chromosomal localizations 总被引:1,自引:0,他引:1