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41.
Mannoor K Matejuk A Xu Y Beardall M Chen C 《Journal of immunology (Baltimore, Md. : 1950)》2012,188(8):3628-3638
Natural autoantibodies (NAA) and their associated B cells constitute a substantial proportion of the normal Ab and B cell repertoire. They often have weak reactivity toward a variety of self-Ags such as DNA, nucleoproteins, and phospholipids. It remains controversial whether NAA contribute to or protect from autoimmune diseases. Using site-directed transgenic (sd-tg) mice expressing a prototypic NAA, we investigated the effect of NAA and NAA-producing B cells in disease development in the autoimmune-prone MRL/MpJ-Fas(lpr) (MRL-lpr) mice. We found that the expression of NAA in MRL-lpr mice prevented proteinuria and reduced kidney immune complex formation. The mice had significantly improved survival. Administration of the IgM NAA to MRL-lpr mice also delayed the onset of nephritis. The sd-tg MRL-lpr mice had decreased levels of anti-dsDNA Abs, anti-Hep2 nuclear Abs, and anti-Sm/ribonucleoprotein Abs. There is a shift in the IgG subclass profile from IgG2a and IgG3 to IgG1 in the sd-tg MRL-lpr mice. The CD4(+) T cells from the sd-tg MRL-lpr mice had increased expression of the negative costimulatory molecule CTLA-4 and increased production of IL-10 as compared with those from the wild-type mice. Furthermore, the NAA B cells produced large amounts of IL-10 upon TLR stimulation. These results indicate that NAA and NAA-producing B cells play an important role in protection from lupus nephritis and suggest that the NAA B cells may have an immune regulatory function via the provision of IL-10. 相似文献
42.
Diatoms and other phytoplankton in coastal waters experience rapid pH changes in milieu due to high biological activities and/or upwelled CO2-rich waters. While CO2 concentrating mechanisms (CCMs) are employed by all diatoms tested to counter low CO2 availability in seawater, little is known how this mechanism responds to fast pH changes. In the present study, the model diatom Thalassiosira pseudonana was acclimated for 20 generations to low pH (7.81) at an elevated CO2 of 1000 μatm (HC) or to high pH (8.18) at ambient CO2 levels of 390 μatm (LC), then its physiological characteristics were investigated as cells were shifted from HC to LC or vice versa. The maximal electron transport rate (ETRmax) in the HC-acclimated cells was immediately reduced by decreased CO2 availability, showing much lower values compared to that of the LC-acclimated cells. However, the cells showed a high capacity to regain their photochemical performance regardless of the growth CO2 levels, with their ETRmax values recovering to initial levels in about 100 min. This result indicates that this diatom might modulate its CCMs quickly to maintain a steady state supply of CO2, which is required for sustaining photosynthesis. In addition, active uptake of CO2 could play a fundamental role during the induction of CCMs under CO2 limitation, since the cells maintained high ETR even when both intracellular and periplasmic carbonic anhydrases were inhibited. It is concluded that efficient regulation of the CCM is one of the key strategies for diatoms to survive in fast changing pH environment, e.g. for the tested species, which is a dominant species in coastal waters where highly fluctuating pH is observed. 相似文献
43.
Jackie H. Myers John Beardall Graeme Allinson Scott Salzman Simon Robertson Leanne Gunthorpe 《Hydrobiologia》2011,671(1):165-180
Nodularia spumigena, like many cyanobacteria, produces specialised reproductive structures, known as akinetes, which are believed to allow survival
under unfavourable conditions. This study investigated the effects of salinity, nitrogen and phosphorus concentration at two
irradiances on akinete differentiation in a N. spumigena isolate from the Gippsland Lakes, Victoria, Australia. A computer image analysis program was used to photograph filaments
and assess production of akinetes over time in separate experiments for each environmental parameter. Heterocyst production
and cell morphology were also examined. The results suggest that akinete production increases over time. Production of akinetes
is further increased at low and high salinities and with the addition of nitrate. Higher irradiance increases akinete differentiation,
although in combination with different phosphorus concentrations causes varied effects. The development and sedimentation
of akinetes may provide an inoculum for reoccurring blooms. Heterocysts were only observed during experiments with varying
salinity and nitrogen exposures. Light quantity appeared to play a large role in heterocyst production. The ability of N. spumigena to produce akinetes and heterocysts is likely to be part of the reason for its success and continual occurrence in estuarine
environments low in nitrogen, such as the Gippsland Lakes, Victoria, Australia. Factors known to reduce heterocyst and akinete
production will provide new insight to possible management controls for this species. 相似文献
44.
Raven JA Johnston AM Kübler JE Korb R McInroy SG Handley LL Scrimgeour CM Walker DI Beardall J Clayton MN Vanderklift M Fredriksen S Dunton KH 《Annals of botany》2002,90(4):525-536
Much evidence suggests that life originated in hydrothermal habitats, and for much of the time since the origin of cyanobacteria (at least 2.5 Ga ago) and of eukaryotic algae (at least 2.1 Ga ago) the average sea surface and land surface temperatures were higher than they are today. However, there have been at least four significant glacial episodes prior to the Pleistocene glaciations. Two of these (approx. 2.1 and 0.7 Ga ago) may have involved a 'Snowball Earth' with a very great impact on the algae (sensu lato) of the time (cyanobacteria, Chlorophyta and Rhodophyta) and especially those that were adapted to warm habitats. By contrast, it is possible that heterokont, dinophyte and haptophyte phototrophs only evolved after the Carboniferous-Permian ice age (approx. 250 Ma ago) and so did not encounter low (=5 degrees C) sea surface temperatures until the Antarctic cooled some 15 Ma ago. Despite this, many of the dominant macroalgae in cooler seas today are (heterokont) brown algae, and many laminarians cannot reproduce at temperatures above 18-25 degrees C. By contrast to plants in the aerial environment, photosynthetic structures in water are at essentially the same temperature as the fluid medium. The impact of low temperatures on photosynthesis by marine macrophytes is predicted to favour diffusive CO(2) entry rather than a CO(2)-concentrating mechanism. Some evidence favours this suggestion, but more data are needed. 相似文献
45.
Chlorella emersonii Shihira et Krauss var. emersonii exhibits ‘C4-like’ gas exchange characteristics when grown at air levels of CO2, but is ‘C3-like’ when grown with extra CO2. The total inorganic carbon concentration, and the free CO2 concentration, averaged over the cell interior are higher in air-adapted cells than can be accounted for by passive CO2 equilibration from the medium and the mean intracellular pH value. The ‘extra’ inorganic C in the air-grown cells probably cannot all be accounted for in terms of binding to proteins and requires an active transport process to account for it. The electrical potential of the cell interior becomes more negative when the ‘CO2 concentrating mechanism’ is operative; this is most readily explained if the active step in inorganic C accumulation is primary active uniport of HCO3?. Since the ‘CO2 concentrating mechanism’ can operate when CO2 is the species crossing the outer permeation barrier, it is suggested that the site of active HCO3? transport in Chlorella (and other eukaryotes) is the chloroplast envelope, and the plasmalemma in cyanobacteria. This scheme explains the obligatory role of the de-repressed carbonic anhydrase in C4-like photosynthesis in algae, but some other data support an explanation of C4-like photosynthesis in terms of special properties of carbonic anhydrase as a carbon donor to RuBP carboxylase-oxygenase. 相似文献
46.
Rapid light curves (RLCs), based on pulse amplitude modulated (PAM) fluorometry, were used to investigate the spatio-temporal variability in photosynthesis versus irradiance parameters (α, Ik and Pmax) and the Fv/Fm ratio of the seagrass Zostera tasmanica (formerly Heterozostera tasmanica). Spatial variation was examined across scales ranging from within a leaf (cms) to across the bed (ms), using a nested analysis of covariance sampling design. Overall, significant variation was identified at all scales examined, excluding the largest scale (area). Patterns of variability differed among individual parameters; however a high percentage of the variation was consistently assigned to the covariates, age (within and between leaves) for all parameters, except Pmax. 相似文献
47.
Philip Heraud Slobodanka Stojkovic John Beardall Don McNaughton Bayden R. Wood 《Journal of phycology》2008,44(5):1335-1339
Macromolecular variability in microalgal populations subject to different nutrient environments was investigated, using the chlorophyte alga Scenedesmus quadricauda (Turpin) Bréb. as a model organism. The large size of the four‐cell coenobia in the strain used in this study (~35 μm diameter) conveniently allowed high quality spectra to be obtained from individual coenobia using a laboratory‐based Fourier transform infrared (FTIR) microscope with a conventional globar source of IR. By drawing sizable subpopulations of coenobia from two Scenedesmus cultures grown under either nutrient‐replete or P‐starved conditions, the population variability in macromolecular composition, and the effects of nutrient change upon this, could be estimated. On average, P‐starved coenobia had higher carbohydrate and lower protein absorbance compared with P‐replete coenobia. These parameters varied between coenobia with histograms of the ratio of absorbance of the largest protein and carbohydrate bands being Gaussian distributed. Distributions for the P‐replete and P‐starved subpopulations were nonoverlapping, with the difference in mean ratios for the two populations being statistically significant. Greater variance was observed in the P‐starved subpopulation. In addition, multivariate models were developed using the spectral data, which could accurately predict the nutrient status of an independent individual coenobium, based on its FTIR spectrum. Partial least squares discriminant analysis (PLS‐DA) was a better prediction method compared with soft independent modeling by class analogy (SIMCA). 相似文献
48.
Phosphate‐limited and phosphate‐sufficient continuous cultures of the marine chlorophyte microalga Dunaliella tertiolecta Butcher were examined for their responses to the addition of phosphate. Phosphate‐limited cultures showed a marked quenching of chl fluorescence following a pulse of phosphate. This response was absent from cells growing under phosphate‐sufficient conditions. Both the extent of fluorescence quenching (where present) and the initial rate of change in quenching were dependent on the concentration of phosphate added to cell suspensions and on the degree of limitation (growth rate in continuous culture). The addition of phosphate also brought about a transient decrease in photosynthetic oxygen evolution and a stimulation in respiration, which were relaxed as the added phosphate was depleted from the external medium. The applicability of using nutrient‐induced fluorescence transients as a tool to identify the nutrient status of phytoplankton populations is discussed. 相似文献
49.
Raven JA Beardall J Chudek JA Scrimgeour CM Clayton MN McInroy SG 《Phytochemistry》2001,58(3):389-394
The linear hexitol altritol has only been identified in six genera, all of them in the order Fucales of the brown algae. Five of these genera are closely related according to molecular phylogenetic and other data, while the sixth (Notheia) is an obligate epiphyte on two other altritol-containing genera with which it is symphanic. The possibility that Notheia obtains altritol from the algae on which it is epiphytic rather than by synthesizing altritol independently was investigated by supplying 13C-inorganic carbon in the light followed by mass spectrometric and nuclear magnetic resonance analysis. Notheia separated from the phorophyte Hormosira during exposure to 13C showed 13C enrichment in both altritol and mannitol, while the Hormosira only showed significant labelling of mannitol. These data show that altritol can be synthesized by Notheia, with implications for the number of gains and losses of the capacity to synthesize altritol in the evolution of the Fucales. 相似文献
50.
Mario Giordano Mustafa Kansiz Philip Heraud John Beardall Bayden Wood Don McNaughton 《Journal of phycology》2001,37(2):271-279
Fourier Transform Infrared (FT-IR) spectroscopy was used to study carbon allocation patterns in response to changes in nitrogen availability in the diatom Chaetoceros muellerii Lemmerman. The results of the FT-IR measurements were compared with those obtained with traditional chemical methods. The data obtained with both FT-IR and chemical methods showed that nitrogen starvation led to the disappearance of the differences in cell constituents and growth rates existing between cells cultured at either high [NO3 − ] or high [NH4 + ]. Irrespective of the nitrogen source supplied before nitrogen starvation, a diversion of carbon away from protein, chlorophyll, and carbohydrates into lipids was observed. Under these conditions, cells that had previously received nitrogen as nitrate appeared to allocate a larger amount of mobilized carbon into lipids than cells that had been cultured in the presence of ammonia. All these changes were reversed by resupplying the cultures with nitrogen. The rate of protein accumulation in the N-replete cells was slower than the rate of decrease under nitrogen starvation. This study demonstrates that the relative proportions of the major macromolecules contained in microalgal cells and their changes in response to external stimuli can be determined rapidly, simultaneously, and inexpensively using FT-IR. The technique proved to be equally reliable to and less labor intensive than more traditional chemical methods. 相似文献