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951.
Masson pine (Pinus massoniana L.) trees in the Pearl River Delta have shown growth decline since late 1980s, particularly those around industrially polluted
regions. As nitrogen is an important nutritional element composing functional proteins, structural proteins and photosynthetic
machinery, investigation on nitrogen allocation is helpful to understand nutrient alteration and its regulation mechanism
in response to pollution stress. Current year (C) and 1-year old needles (C + 1) of five mature trees were sampled in industrially
polluted site and unpolluted natural reserve for bioassay. Needles of declining trees had significantly higher leaf nitrogen
per unit area (NL) but lower photosynthetic capacity (P
max), which resulted in lower photosynthetic nitrogen use efficiency (PNUE) than those of healthy trees. Nitrogen fraction to
the photosynthetic apparatus in the C and C + 1 needles at polluted site was 27 and 22%, significantly lower than the corresponding
healthy needles (48 and 32%). The content of structural proteins was positively correlated with NL in C and C + 1 needles. Moreover, the C and C + 1 needles of declining trees had about 1.8 times structural protein as those
of healthy trees, suggesting that more nitrogen allocation to structural protein are needed for stronger structural defenses
under polluted stress. Decreases in PNUE of declining pine trees could be partially explained by increases in structural protein
nitrogen. 相似文献
952.
953.
Leonardo Mata Helena Gaspar Fátima Justino Rui Santos 《Journal of applied phycology》2011,23(5):827-832
The genus Asparagopsis is a prolific source of halogenated metabolites. Due to its commercial applications, it has been intensively cultivated in southern Portugal. In the present study, we assess if the internal levels of the major halogenated metabolites (bromoform and dibromoacetic acid) in Asparagopsis taxiformis can be increased with hydrogen peroxide (H2O2) addition. Previous studies with red algae showed that the production/release of bromoform can be enhanced by exogenously supplying H2O2. However, no study has assessed if H2O2 supply enhances the content of secondary metabolites within the biomass. This detail is important as the objective of the proposed research is to enhance the content of these valuable metabolites in the produced biomass. Both the activity of the haloperoxidase enzyme and the metabolite content were assessed on short-term and long-term incubation periods to H2O2. To determine the susceptibility of A. taxiformis photosynthetic performance to the imposed oxidative stress, the in vivo fluorescence of photosystem II was monitored. A. taxiformis was shown to be physiologically vulnerable to H2O2, given the observed decrease of the maximum quantum yield of photosynthesis (F v/F m). Contrary to what was expected, the presence of H2O2 inhibited the activity of the iodoperoxidase enzyme. Nevertheless, the extracted halogenated metabolites were higher over the first hours of exposure to H2O2, decreasing after 48 h. These results are probably related to the prosthetic group of the halogenated enzyme in A. taxiformis and the long-term oxidative stress damage of H2O2 exposure. Considering the objective of the proposed research, addition of H2O2 to the cultures, prior (3 h) to biomass harvesting, increases the metabolite content. 相似文献
954.
Leal E Fernández-Durán B Guillot R Ríos D Cerdá-Reverter JM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(8):1035-1044
Repetitive aquaculture-related protocols may act as cyclic stressors that induce chronic stress in cultured fish. The sea
bass is particularly sensitive to stressful conditions and the mere presence of humans will disturb feeding behavior. In this
paper, we study whether chronic stress induced by repetition of acute stress protocols affects long-term feeding behavior
and growth performance in sea bass and whether exogenous cortisol may induce stress-like changes in these parameters. We demonstrate
that both chronic stress and dietary cortisol decrease food intake and have a negative effect on feed conversion efficiency,
severely impairing sea bass performance. Both experimental approaches induced changes in the daily feeding activity by lengthening
the active feeding periods. Fish subjected to a cyclic stressor modify their daily feeding pattern in an attempt to avoid
interference with the time of the stressor. The delay in feeding when fish are acutely and repeatedly stressed could be of
substantial adaptive importance. 相似文献
955.
David C. Queller 《Biology & philosophy》2011,26(6):905-913
Biologists and philosophers differ on whether selection should be analyzed at the level of the gene or of the individual. In Peter Godfrey-Smith’s book, Darwinian Populations and Natural Selection, he argues that individuals can be good members of Darwinian populations, whereas genes rarely can. I take issue with parts of this view, and suggest that Godfrey-Smith’s scheme for thinking about Darwinian populations is also applicable to populations of genes. 相似文献
956.
Indicators for photoreactivation and dark repair studies following ultraviolet disinfection 总被引:1,自引:0,他引:1
Repair of DNA in bacteria following ultraviolet (UV) disinfection can cause reactivation of inactivated bacteria and negatively impact the efficiency of the UV disinfection process. In this study, various strains of E. coli (wild-type, UV-resistant and antibiotic-resistant strains) were investigated for their ability to perform dark repair and photoreactivation, and compared based on final repair levels after 4 h of incubation, as well as repair rates. Analysis of the results revealed that the repair abilities of different E. coli strains can differ quite significantly. In photoreactivation, the log repair ranged from 10 to 85%, with slightly lower log repair percentages when medium-pressure (MP) UV disinfection was employed. In dark repair, log repair ranged from 13 to 28% following low-pressure (LP) UV disinfection. E. coli strains ATCC 15597 and ATCC 11229 were found to repair the fastest and to the highest levels for photoreactivation and dark repair, respectively. These strains were also confirmed to repair to higher levels when compared to a pathogenic E. coli O157:H7 strain. Hence, these strains could possibly serve as conservative indicators for future repair studies following UV disinfection. In addition, dimer repair by photoreactivation and dark repair was also confirmed on a molecular level using the endonuclease sensitive site (ESS) assay. 相似文献
957.
Conjugative plasmids play a very important role in bacterial adaptation through the dissemination of useful traits. Incompatibility
group P-1 (IncP-1) plasmids exhibit an extreme broad-host-range among Gram-negative bacteria and known to be one of the major
agents to disseminate various phenotypic traits such as antibiotic resistance and xenobiotic degradation. Although the plasmids
are believed to be very stable in most Gram-negative bacteria, little is known about the factors that affect their stability
in various hosts, allowing their persistence in bacterial population. Here we show that the stability of the cryptic IncP-1β
plasmid pBP136 differed greatly in four different Escherichia coli K12 host backgrounds (MG1655, DH5α, EC100, and JM109), whereas the closely related plasmid pB10 was stable in all four strains.
The supply of the kleF gene, which is involved in the stability of IncP-1 plasmids but absent in pBP136, did not improve the stability of the plasmid.
Our findings suggest that persistence of IncP-1 plasmids in the absence of selection is affected by strain-specific factors. 相似文献
958.
The behavior of Na/K pump currents when exposed to an oscillating electric field is studied by computer simulation. The pump
current from a single pump molecule was sketched based on previous experimental results. The oscillating electric field is
designed as a symmetric, dichotomous waveform varying the membrane potential from −30 to −150 mV around the membrane resting
potential of −90 mV. Based on experimental results from skeletal muscle fibers, the energy needed to overcome the electrochemical
potentials for the Na and K-transports are calculated in response to the field’s two half-cycles. We found that a specially
designed oscillating electric field can eventually synchronize the pump molecules so that all the individual pumps run at
the same pumping rate and phase as the field oscillation. They extrude Na ions during the positive half-cycle and pump in
K ions during the negative half-cycle. The field can force the two ion-transports into the corresponding half-cycles, respectively,
but cannot determine their detailed positions. In other words, the oscillating electric field can synchronize pumps in terms
of their pumping loops but not at a specific step in the loop. These results are consistent with our experimental results
in measurement of the pump currents. 相似文献
959.
Graciela Gil-Romera Mercedes García Antón Juan A. Calleja 《Vegetation History and Archaeobotany》2008,17(6):653-666
New pollen results and radiocarbon dating from a valley mire in south-western Spain are presented. This is a region where
few palaeoecological records have been preserved and the sequence yields important new palaeobotanical evidence for the late
Holocene. The landscape is shown as having been largely open woodland, but more wooded than at present. The vegetation history
of the last four millennia in these montane territories of south-western Iberia is discussed in the light of anthropogenic
indicators, archaeological and documentary archives; fire incidence and climate change. Alnus is the predominant pollen type, although a decline is noted during the last couple of centuries. Its presence is connected
with local topography behaving as a phreatophyte, that is, a plant which obtains a significant amount of water from the zone
of saturated soil. A framework is also provided for the age and ecological dynamics of some major woodland taxa—Betula, Corylus, Ilex, evergreen and deciduous oaks, Ericaceae and Pinus. In addition, the natural status of several pollen taxa and local trends in biodiversity are discussed. We consider that
the results of our work will have important implications for the understanding of the vegetation history in a floristically
very rich area, with a noticeable diversity of woody taxa, and a relatively well preserved ecosystem structure. 相似文献
960.
Samuli Helama Matti Vartiainen Taneli Kolström Heli Peltola Jouko Meriläinen 《Vegetation History and Archaeobotany》2008,17(6):675-686
A collection of subfossil wood of Pinus sylvestris (Scots pine) was exposed to X-ray densitometry. The collection of 64 samples from the southern boreal forest zone was dendrochronologically
cross-dated to a.d. 673-1788. Growth characteristics were determined by performing density profiles including the following parameters: minimum
density, earlywood and latewood boundary density, maximum density, earlywood width, earlywood density, latewood width, latewood
density, annual ring width and annual ring density. Seven out of the nine parameters were found to contain non-climatic growth
trends and six were found to be heteroscedastic in their variance. Tree-specific records were indexed, to remove the non-climatic
growth trends and stabilize the variance, and combined into nine parameter-specific tree-ring chronologies. Growth characteristics
of the pines changed in parallel with the generally agreed climatic cooling from the Medieval Warm Period to the Little Ice
Age: pine tree-rings showed decreasing maximum densities from the period a.d. 975-1150 to a.d. 1450–1625. A concomitant change in the intra-annual growth characteristics was detected between these periods. The findings
indicate that not only the trees growing near the species’ distributional limits are sensitive to large-scale climatic variations
but also the trees growing in habitats remote from the timberline have noticeably responded to past climate changes. 相似文献