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41.
Function of Peptide Antibiotics in Sporulation 总被引:13,自引:0,他引:13
42.
The polyoma-induced transplantation antigen is virus specific and its presence on polyoma transformed but not normal cells suggested that at least part of the polyoma genome is maintained in tumour cells. Studies reported here indicate that malignancy is not maintained solely by the presence of this transplantation antigen. 相似文献
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DAVID T. TINGEY ROBERT B. MCKANE DAVID M. OLSZYK MARK G. JOHNSON PAUL T. RYGIEWICZ E. HENRY LEE 《Global Change Biology》2003,9(7):1038-1050
The effects of elevated CO2 and temperature on principal carbon constituents (PCC) and C and N allocation between needle, woody (stem and branches) and root tissue of Pseudotsuga menziesii Mirb. Franco seedlings were determined. The seedlings were grown in sun‐lit controlled‐environment chambers that contained a native soil. Chambers were controlled to reproduce ambient or ambient +180 ppm CO2 and either ambient temperature or ambient +3.5 °C for 4 years. There were no significant CO2 × temperature interactions; consequently the data are presented for the CO2 and temperature effects. At the final harvest, elevated CO2 decreased the nonpolar fraction of the PCC and increased the polar fraction and amount of sugars in the needles. In contrast, elevated temperature increased the nonpolar fraction of the PCC and decreased sugars in needles. There were no CO2 or temperature effects on the PCC fractions in the woody tissue or root tissue. Elevated CO2 and temperature had no significant effects on the C content of any of the plant tissues or fractions. In contrast, the foliar N content declined under elevated CO2 and increased under elevated temperature; there were no significant effects in other tissues. The changes in the foliar N concentrations were in the cellulose and lignin fractions, the fractions, which contain protein, and are the consequences of changes in N allocation under the treatments. These results indicate reallocation of N among plant organs to optimize C assimilation, which is mediated via changes in the selectivity of Rubisco and carbohydrate modulation of gene expression. 相似文献
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1. We investigated the role of algal composition on pumping, clearance, assimilation, pseudofaeces and faeces production, feeding time budgets, and condition of zebra mussels from spring to autumn at two sites in Saginaw Bay (Lake Huron) and one site in western Lake Erie. Size‐fractioned chlorophyll was used to distinguish between feeding on small (<53 μm) and large (>53 μm) size fractions, and mussel feeding behaviour was quantified by video observations. 2. Mussel pumping, clearance and assimilation rates varied among sites, particularly during summer, when phytoplankton composition varied considerably among sites. Lowest values were seen at the inner‐bay site of Saginaw Bay, low to moderate values at the outer‐bay site of Saginaw Bay, and high values at the Lake Erie site. Clearance, pumping and assimilation rates were all highly positively correlated (R2 = 0.76) with per cent contribution of flagellates to total algal biomass and negatively correlated with per cent of Microcystis aeruginosa (R2 = 0.63). The negative effects on pumping rate (as determined by clearance rate on the <53 μm fraction) of Microcystis, which occurred in the >53 μm fraction, could be mitigated by the presence of flagellates in the <53 μm fraction. 3. Visual observations of mussel feeding showed evidence for poor seston quality during summer negatively affecting feeding rates. High faeces production during times of low assimilation rate was suggestive of poor assimilation efficiency and/or viable gut passage of grazing resistant algae. Long periods of time not filtering by the mussels during some Microcystis blooms and lack of production of a filtering current during one experiment were suggestive of intoxication from microcystin or other secondary compounds. 4. Clearance and feeding rates of the mussels in Saginaw Bay were high during spring and autumn and very low in summer, particularly at the inner‐bay site. Condition of the mussels (mass : length ratio) was highest in spring and lowest during summer. This seasonal variation probably reflected high food assimilation rate during autumn and spring and low assimilation rate and reproduction during summer. The condition of mussels throughout the year was higher at the outer‐bay than the inner‐bay site, reflecting better feeding conditions at the former. Mussel selective feeding may have been responsible for the poor quality of food at the inner bay site; therefore, we postulate that a regime shift in phytoplankton composition promoted by the mussels fed back into lowered condition of the mussels. 相似文献
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Interactions between wild carnivore abundance and landscape composition in agricultural landscapes are poorly understood despite their importance to both production and conservation. In Australia, introduced red foxes (Vulpes vulpes) prey on both native species and lambs in the temperate agricultural regions. Historically these areas were extensively cleared of native vegetation. Recently revegetation programmes have been implemented, but there is concern that this may benefit foxes and hence increase their impacts. We used an artificial prey placed in eight revegetated (6–12% cover) and 10 cleared (0–1.5% cover) landscapes of ~700 ha to assess how these landscapes influenced fox predation rates. In June and August 2006 (winter) when we expect fox populations to be relatively stable following juvenile dispersal, predation rates were 1.5–2 times higher in revegetated landscapes than in cleared landscapes. We found no evidence of microhabitat effects on predation rates suggesting these landscape‐level differences were probably due to differences in fox population density. In April 2007 (autumn) the results were more variable, possibly indicating more transient populations including dispersing juveniles at this time. Our results suggest that the impact of foxes on highly vulnerable prey could increase with revegetation. However, the benefits of revegetation to prey may offset negative impacts of foxes and future work is required to assess the likely net effects. 相似文献
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Peroxidase-containing enzyme supernatant preparations of tobaccoabscission zone flower pedicel tissue sections of ethylene-treatedand untreated Nicotiana tabacum L. plants were assayed for u.v.absorption spectra with and without the addition of IAA. Theu.v. spectral absorption of peroxidase-catalysed IAA oxidationindicated that there is not an appreciable difference in absorbancepeaks in the ethylene-treated plants compared with untreatedcontrols, in the presence of added IAA; however, the ethylene-treatedtissues alone show different absorption peak values in the 1,2, 3, 4, 4.5, and 5 h samples. These results are discussed inrelation to ethylene-induced peroxidase activity in tobaccoflower pedicel abscission zone tissue homogenates. 相似文献
50.
Thomas, H. 1987. Physiological responses to drought of Loliumperenne L.: Measurement of, and genetic variation in, waterpotential, solute potential, elasticity and cell hydration.J.exp. Bot. 38: 115125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (w) osmoticpotential (s), turgor potential (p = w s), elasticity(E), leaf hydration (g water per g dry matter, H) and numberof green leaves per tiller (NGL) were measured before and duringa 42 d drought treatment. A simplified method of estimating E (at w < 1?0 MPa) usingonly six measurements was developed to permit a measurementrate of 8 leaves per hour. Measurement errors in all characterswere 3% or less. During drought, w and s (at w = 0?5 MPa) decreased significantly,p and E increased significantly, and H decreased slightly. Plantsize during drought was negatively correlated with s, and Hand positively correlated with p, osmotic adjustment, E andNGL. Measurements made on the genotypes before draughting didnot give a reliable indication of their physiological conditionafter adaptation to drought. Genetically controlled variation (broad sense heritability)of drought-adapted plants for E was 15%, w 23%, s, 34%, p, 35%,H 34% and NGL 64%. The possibilities for, and effectivenessof, divergent selection of genotypes with high and low expressionof the characters are discussed. Key words: Water relations, Lolium, genetic variation 相似文献