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21.
The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level. 相似文献
22.
The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone 总被引:30,自引:1,他引:29 下载免费PDF全文
The basis of inhibition of photosynthesis by single acute O3 exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O3 for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO2 uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO2 uptake and the internal CO2 concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O3; no significant increase occurred for any of the other treatments. Analysis of the response of CO2 uptake to the internal CO2 concentration implied that the predominant factor responsible for the reduction in light-saturated CO2 uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O3, respectively. At saturating concentrations of CO2, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O3. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO2 uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O3, requiring 8 hours at 400 nanomoles per mole O3 before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO2 uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O3 fumigation. 相似文献
23.
Effect of light/dark cycles on expression of nitrate assimilatory genes in maize shoots and roots 总被引:8,自引:2,他引:6 下载免费PDF全文
The level of nitrate reductase (NR) and nitrite reductase (NiR) varied in both shoot and root tissue from nitrate-fed Zea mays L. grown under a 16-hour light/8-hour dark regime over a 10-day period postgermination, with peak activity occurring in days 5 to 6. To study the effect of different light regimes on NR and NiR enzyme activity and mRNA levels, 6-day-old plants were grown in the presence of continuous KNO3 (10 millimolar). Both shoot NRA and mRNA varied considerably, peaking 4 to 8 hours into the light period. Upon transferring plants to continuous light, the amplitude of the peaks increased, and the peaks moved closer together. In continuous darkness, no NR mRNA or NR enzyme activity could be detected by 8 hours and 12 hours, respectively. In either a light/dark or continuous light regime, root NRA and mRNA did not vary substantially. However, when plants were placed in continuous darkness, both declined steadily in the roots, although some remained after 48 hours. Although there was no obvious cycling of NiR enzyme activity in shoot tissue, changes in mRNA mimicked those seen for NR mRNA. The expression of NR and NiR genes is affected by the light regime adopted, but light does not have a direct effect on the expression of these genes. 相似文献
24.
C. M. STIRLING G. Y. NIE C. AGUILERA A. NUGAWELA S. P. LONG N. R. BAKER 《Plant, cell & environment》1991,14(9):947-954
Abstract. The effect of growth temperatures on quantum yield (φ) was examined for leaves at different stages of development within the immature canopies of two crops of field grown maize ( Zea mays cv. LG11) sown on 3 May and 20 June 1990. During the period of 23 to 49d after sowing, the crop sown on the 3 May experienced temperatures below 10°C on 19 occasions compared with only two for the crop sown on 20 June. A period of severe chilling at the end of May and the beginning of June was associated with a marked reduction in φ for all leaves in the early-sown crop. This chill-induced depression in φ was greater in recently emerged than more mature leaves in the canopy and was found to be accompanied by modifications in the polypeptide profiles of thylakoids isolated from the leaves. During the chilling period, decreases in some polypeptides, notably in the range of 41–42 and 20kDa apparent molecular size, and increases of polypeptides of c. 15–16kDa were observed compared with leaves developing at warmer temperatures in July. The efficiency of converting intercepted radiation into dry matter (conversion efficiency) was 42% lower in the early- than late-sown crop, but no significant relationship between conversion efficiency and quantum yield was found in either treatment. 相似文献
25.
Daina H. Simmonds Nancy E. Long Wilfred A. Keller 《Plant Cell, Tissue and Organ Culture》1991,27(3):231-241
Protoplasts were isolated from an embryogenic cell suspension culture derived from microspores of Brassica napus cv. Jet Neuf. Protoplast yield varied with the cell suspension growth medium. Optimization of protoplast plating density, manipulation of culture medium, carbon source and medium matrix, and inclusion of Ficoll resulted in protoplast plating efficiencies close to 30%. Placement of the protoplasts close to the gas interface contributed greatly to the elevated plating efficiency. Low density cultures could be induced to regenerate calli at optimum plating efficiencies if grown in the presence of nurse culture. This is of great advantage for manipulation of individual protoplasts or for microinjection. Plants were regenerated directly from the cell suspension or from the protoplast cultures.Abbreviations BA
N6-benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IAA
indole-3-acetic acid
- NAA
naphthaleneacetic acid 相似文献
26.
Barbara Kluve-Beckerman George L. Long Merrill D. Benson 《Biochemical genetics》1986,24(11-12):795-803
Serum amyloid A (SAA) is an acute-phase reactant and precursor to amyloid A protein, the major constituent of the fibril deposits of reactive amyloidosis. The factors determining whether the 104-amino acid SAA molecule is converted into the 76-amino acid amyloid A protein and deposited as fibrils are not known. As an initial step toward investigating the possibility that a particular primary structure of SAA is involved in amyloid formation, we have cloned and determined the nucleotide sequence of human SAA-specific cDNAs. The first clone, selected using an oligonucleotide probe, was shown to encode the signal peptide and amino-terminal region of SAA. The cDNA of this clone served as probe in the selection of two distinct, full-length SAA cDNAs, initially differentiated by the presence (pSAA21) or absence (pSAA82) of a PstI site in the coding sequence. The complete nucleotide sequence of pSAA82 cDNA was determined. Since there appear to be multiple human SAA alleles, it is conceivable that their differential expression is important to amyloid formation. 相似文献
27.
Monoclonal antibody that inhibits infection of HeLa and rhabdomyosarcoma cells by selected enteroviruses through receptor blockade. 总被引:14,自引:11,他引:3 下载免费PDF全文
R L Crowell A K Field W A Schleif W L Long R J Colonno J E Mapoles E A Emini 《Journal of virology》1986,57(2):438-445
BALB/c mice were immunized with HeLa cells, and their spleen cells were fused with myeloma cells to produce hybridomas. Initial screening of culture fluids from 800 fusion products in a cell protection assay against coxsackievirus B3 (CB3) and the CB3-RD virus variant yielded five presumptive monoclonal antibodies with three specificities: protection against CB3 on HeLa, protection against CB3-RD on rhabdomyosarcoma (RD) cells, and protection against both viruses on the respective cells. Only one of the monoclonal antibodies (with dual specificity) survived two subclonings and was studied in detail. The antibody was determined to have an immunoglobulin G2a isotype and protected cells by blockade of cellular receptors, since attachment of [35S]methionine-labeled CB3 was inhibited by greater than 90%. The monoclonal antibody protected HeLa cells against infection by CB1, CB3, CB5, echovirus 6, and coxsackievirus A21 and RD cells against CB1-RD, CB3-RD, and CB5-RD virus variants. The monoclonal antibody did not protect either cell type against 16 other immunotypes of picornaviruses. The monoclonal antibody produced only positive fluorescence on those cells which were protected against infection, and 125I-labeled antibody confirmed the specific binding to HeLa and RD cells. The results suggest that this monoclonal antibody possesses some of the receptor specificity of the group B coxsackieviruses. 相似文献
28.
Lars Werdelin John A. Long 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1986,19(2):161-169
A set of 18 measurements of the dermal armour of Bothriolepis canadensis Whiteaves (Placodermi, Anti-archa) is analysed with respect to allometric growth patterns. The strongest allometric patterns were found for the orbital fenestra and premedian plate of the head-shield. and the anterior median dorsal plate of the trunk-shield. These are all areas of the greatest importance in antiarch phylogeny and imply a role for ontogenetic effects such as paedomorphosis in the evolution of antiarchs. It is suggested that this is partly a result of the severe constraints on growth in a closed box such as the armour of placoderms, and may be generally true of such arrangements. 相似文献
29.
Summary An indirect test of the relationship between leaf area and the combination of mean size and density is made in stands of lodgepole pine (Pinus contorta Dougl.). Total sapwood cross-sectional area of these stands is a function of the product of density and mean diameter raised to an exponent of about 1.6. Results from other studies, representing four species, suggest that this relationship between sapwood area and the combination of mean size and density may be general. The implications of the relationship are discussed in the context of evapotranspiration, competition and self-thinning.Utah Agricultural Experiment Station Journal Paper No. 3072 相似文献
30.
Summary The tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined for its ability to induce endogenous retrovirus from a high-passage clone
of Kirsten sarcoma virus-transformed Balb/c (K-Balb) mouse cells. TPA activated virus in a concentration-dependent manner
(0.0016 to 4.0 μM). Exposure to 1mM actinomycin D inhibited virus induction, suggesting that cellular RNA synthesis is required de novo by this inducer. A broad-spectrum
neutralizing antibody to murine type C virus, gp70, was shown to neutralize the infectivity of the induced virus. The activated
virus had the host range of the xenotropic Balb virus:2, and after removal of the inducer, the activated state decayed rapidly.
TPA stimulated DNA, RNA, and protein synthesis in K-Balb cells, indicating that the mechanism of inducation may be different
from that of previously identified virus inducers. The effects observed using the well-defined K-Balb system offer an opportunity
to study the modulation of retrovirus gene expression by TPA.
This work was conducted while the authors were with the Biological Carcinogenesis Program, Frederick Cancer Research Facility,
Frederick, MD 21701, and was supported under Contract NO1-CO-75380 with the National Cancer Institute, National Institutes
of Health, Bethesda, MD 20205. 相似文献