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911.
Membrane inlet mass spectrometry indicated massive light-dependent cycling of inorganic carbon between the medium and the
cells of various phytoplankton species representing the main groups of aquatic primary producers. These included diatoms,
symbiotic and free living dinoflagellates, a coccolithophorid, a green alga and filamentous and single cell cyanobacteria.
These organisms could maintain an ambient CO2 concentration substantially above or below that expected at chemical equilibrium with HCO3
−. The coccolithophorid Emiliania huxleyishifted from net CO2 uptake to net CO2 efflux with rising light intensity. Differing responses of CO2 uptake and CO2 fixation to changing light intensity supported the notion that these two processes are not compulsorily linked. Simultaneous
measurements of CO2 and O2 exchange and of the fluorescence parameters in Synechococcus sp. strain PCC 7942, showed that CO2 uptake can serve as a sensitive probe of the energy status of the photosynthetic reaction centers. However, during transitions
in light intensity, changes in CO2 uptake did not accord with those expected from fluorescence change. Quantification of the net fluxes of CO2, HCO3
− and of photosynthesis at steady-state revealed that substantial HCO3
− efflux accompanied CO2 uptake and fixation in the case of `CO2 users'. On the other hand, `HCO3
− users' were characterized by a rate of net CO2 uptake below that of CO2 fixation. The results support the notion that entities associated with the CCM function not only in raising the CO2 concentration at the site of Rubisco; they may also serve as a means of diminishing photodynamic damage by dissipating excess
light energy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
912.
Previous studies have shown that in water the affinity of submerged macrophytes for CO2 is higher for species restricted to CO2 than for species with an additional ability to use bicarbonate. We measured slopes of CO2 uptake versus CO2 concentration in the gas phase in air, nitrogen and helium for pairs of species, having or lacking the ability to use bicarbonate,
but with similar leaf morphology. For species restricted to CO2, the slope in nitrogen and helium was 1.5 times and 3.2 times greater than in air. The increased slope in nitrogen results
from a suppression of photorespiration. The further increase in helium reflects the increased rate of diffusion of CO2 and shows that, even in gas, external diffusion through the boundary layer is a significant hindrance to CO2 uptake. In contrast, in species able to use bicarbonate, the uptake slope was not affected by gas composition, suggesting
that photorespiration is absent or photorespired CO2 is efficiently trapped and that internal resistance is high relative to external resistance. Elodea canadensis specimens grown under high concentrations of CO2 de-regulated their ability to use bicarbonate, and slopes of CO2 uptake in helium were significantly greater than in air or nitrogen. Overall, these results are consistent with the notion
that while a high affinity for CO2 will maximise carbon uptake in species restricted to CO2, for species able to use bicarbonate, a high internal resistance would reduce loss of CO2 and help maintain high concentrations of CO2 at the site of fixation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
913.
Trejo-Tapia Gabriela Arias-Castro Carlos Rodríguez-Mendiola Martha 《Plant Cell, Tissue and Organ Culture》2003,72(1):7-12
The effects of the concentration of PO4
3-, NO3
–, Fe 2+, sucrose and inoculum size on the accumulation of blue pigment and growth of suspension cultures of Lavandula spica D.C. (
L. latifolia Vill.), were studied. The combination of 2.5 mM PO4
3-, 14.1 mM NO3
–, 1 mM Fe 2+, 30 g l–1 sucrose and 10 g l–1fresh weight of inoculum, promoted a 7-fold enhancement on the productivity of blue pigment in comparison to the control medium. Among all the culture medium constituents tested, phosphate exerted the highest beneficial effect and Fe2+ showed to be essential for the accumulation of the pigment. High levels of sucrose (60 or 90 g l–1) did not stimulate the accumulation of blue pigment. In these conditions, cell growth and cell viability were drastically affected. 相似文献
914.
Inhibition of catalase activity by oxidative stress and its relationship to salicylic acid accumulation in plants 总被引:15,自引:0,他引:15
Ie-Sung Shim Yukie Momose Akihiro Yamamoto Dea-Wook Kim Kenji Usui 《Plant Growth Regulation》2003,39(3):285-292
The decrease in catalase activity and its relationship to change in salicylic acid content were investigated in rice, wheat, and cucumber seedlings exposed to oxidative stresses. A decrease in chlorophyll fluorescence (F/Fm), measured as an indicator of the oxidative stress, and a drop in catalase activity were observed following treatment with NaCl in all plant seedlings tested . Furthermore, such decreases in F/Fm and catalase activity were also observed under low temperature conditions in both rice cultivars, whereas the degrees of decrease were dependent on their low temperature tolerance . Although the content of salicylic acid increased in rice seedlings stressed by NaCl treatment, it was inversely correlated with the decrease in the catalase activity . Such a relationship between the decrease in catalase activity and increase in salicylic acid content was confirmed with paraquat treatment of the rice seedlings . These results suggested that the fall in catalase activity is a phenomenon occurring in many plant species under oxidative stress and is related to the accumulation of salicylic acid in oxidatively-stressed plants. 相似文献
915.
Preparation and characterization of novel coenzyme Q<Subscript>10</Subscript> nanoparticles engineered from microemulsion precursors 总被引:2,自引:0,他引:2
The purpose of these studies was to prepare and characterize nanoparticles into which Coenzyme Q10 (CoQ10) had been incorporated (CoQ10-NPs) using a simple and potentially scalable method. CoQ10-NPs were prepared by cooling warm microemulsion precursors composed of emulsifying wax, CoQ10, Brij 78, and/or Tween 20. The nanoparticles were lyophilized, and the stability of CoQ10-NPs in both lyophilized form and aqueous suspension was monitored over 7 days. The release of CoQ10 from the nanoparticles was investigated at 37°C. Finally, an in vitro study of the uptake of CoQ10-NPs by mouse macrophage, J774A.1, was completed. The incorporation efficiency of CoQ10 was approximately 74%±5%. Differential Scanning Calorimetry (DSC) showed that the nanoparticle was not a physical mixture
of its individual components. The size of the nanoparticles increased over time if stored in aqueous suspension. However,
enhanced stability was observed when the nanoparticles were stored at 4°C. Storage in lyophilized form demonstrated the highest
stability. The in vitro release profile of CoQ10 from the nanoparticles showed an initial period of rapid release in the first 9 hours followed by a period of slower and
extended release. The uptake of CoQ10-NPs by the J774A.1 cells was over 4-fold higher than that of the CoQ10-free nanoparticles (P<.05). In conclusion, CoQ10-NPs with potential application for oral CoQ10 delivery were engineered readily from microemulsion precursors. 相似文献
916.
Adeola O Ram JI Maenz DD Classen HL 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,135(3):235-247
Luminal polyamines and their absorption are essential for proliferation of the enterocytes and, therefore, nutrition, health and development of the animal. The transport systems that facilitate the uptake of putrescine were characterized in chick duodenal, jejunal and ileal brush-border membrane vesicles prepared by MgCl2 precipitation from three-week-old chicks. An inwardly-directed Na+ gradient did not stimulate putrescine uptake and, therefore, putrescine transport in chick intestine. In the duodenum, jejunum and ileum, kinetics of putrescine transport fitted a model with a single affinity component plus a non-saturable component. The affinity (Kt) for [3H]putrescine transport across the brush-border membrane increased along the length of the small intestine. A model of intermediate affinity converged to the data obtained for [3H]putrescine transport with Kt approximating 1.07 and 1.05 mM or duodenum and jejunum, respectively; and high affinity with a Kt of 0.35 mM for the ileum. The polyamines cadaverine, putrescine, spermidine and spermine strongly inhibited the uptake of [3H]putrescine into chick brush-border membrane vesicles, more so for the jejunum and ileum than the duodenum. The kinetics of cadaverine, spermidine and spermine inhibition are suggestive of competitive inhibition of putrescine transport. These uptake data indicate that a single-affinity system facilitates the intestinal transport of putrescine in the chick; and the affinity of transporter for putrescine is higher in the ileum than in the proximal sections of the small intestine. In addition, this study shows that the ileum of chicks plays an important role in regulating cellular putrescine concentration. 相似文献
917.
The effects of placing solid implants containing Fe sulfate in branches of Fe-deficient pear and peach trees on the composition of the xylem sap have been studied. Iron sulfate implants are commercially used in northeastern Spain to control iron chlorosis in fruit trees. Implants increased Fe concentrations and decreased organic acid concentrations in the xylem sap, whereas xylem sap pH was only moderately changed. The citrate to Fe ratios decreased markedly after implants, therefore improving the possibility that Fe could be reduced by the leaf plasma membrane enzyme reductase, known to be inhibited by high citrate/Fe ratios. In peach, the effects of the implants could be observed many months post treatment. In pear, some effects were still observed one year after the implants had taken place. Results obtained indicate that solid Fe sulfate implants were capable of significantly changing the chemical composition of the xylem sap in fruit trees. 相似文献
918.
Coal mining causes health problems, such as pneumoconiosis. We have previously shown that prevalence of pneumoconiosis in workers from various coalmine regions positively correlates with levels of bioavailable iron (BAI) in the coals from that region. In the present study, the nature of reactive oxygen species formed by BAI in the coals and its mechanisms of the induction of biological responses were investigated. Human lung epithelial cell line, A549 cells, were used to examine the induction of interleukin-6 (IL-6), a pro-inflammatory cytokine, which is known to play a crucial role in the development of pneumoconiosis. We found that levels of IL-6 protein as well as its mRNA were significantly increased in the cells treated for 24 h with 20 microg/cm2 of the BAI-containing Pennsylvania (PA) coal; for example we observed 6.7-fold increase in IL-6 protein. Levels of IL-6 protein in cells treated with the Utah (UT) coal containing low-BAI were only 1.9-fold of the control levels. The enhancing effect on the IL-6 by the PA coal was similar to that caused by hydrogen peroxide. Superoxide dismutase (SOD), catalase (CAT), and N-acetyl-L-cysteine (NAC) all had inhibitory effects on the PA coal-induced IL-6 formation. However, CAT had the least protective effect as compared to SOD and NAC. Our results indicate that BAI in the PA coal may induce IL-6 through both ferryl species (via iron autoxidation) and hydroxyl radicals (via the Fenton/Haber Weiss reactions). 相似文献
919.
AIMS: The aim of the study was to screen the Enterobacteriaceae flora of meat for the presence of bacteria harbouring the Yersinia high-pathogenicity island (HPI). METHODS AND RESULTS: Bacteria from 29 meat and 29 liver samples were isolated on violet-red bile glucose agar. A total of 197 isolates were screened for the presence of the irp2 gene, encoded within the HPI, by PCR. One isolate that was positive for irp2 gene was also positive for the fyuA, irp1, ybtP/ybtQ, ybtX/ybtS and int/asn tRNA genes by PCR. The presence of fyuA, irp1 and irp2 genes was confirmed by Southern hybridization. CONCLUSIONS: The isolate was identified as Serratia liquefaciens by sequencing of the 16S rRNA gene and by ribotyping. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of a Serratia harbouring the Yersinia HPI. Serratia is a frequently occurring Enterobacteriaceae genus in chill-stored meat. 相似文献
920.
Landon LA Peletskaya EN Glinsky VV Karasseva N Quinn TP Deutscher SL 《Journal of Protein Chemistry》2003,22(2):193-204
Thomsen-Friedenreich (TF) antigen occurs on approximately 90% of human carcinomas, is likely involved in carcinoma cell homotypic aggregation, and has clinical value as a prognostic indicator and marker of metastasized cells. Previously, we isolated anti-TF antigen peptides from bacteriophage display libraries. These bound to TF antigen on carcinoma cells but were of low affinity and solubility. We hypothesized that peptide amino acid sequence changes would result in increased affinity and solubility, which would translate into improved carcinoma cell binding and increased inhibition of aggregation. The new peptides were more soluble and exhibited up to fivefold increase in affinity (Kd 60 nM). They bound cultured human breast and prostate carcinoma cells at low concentrations, whereas the earlier peptides did not. Moreover, the new peptides were potent inhibitors of homotypic aggregation. The maturated peptides will have expanded applications in basic studies of the TF antigen and particular utility as clinical carcinoma-targeting agents. 相似文献