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71.
The apparent photosynthetic affinity-for inorganic carbon inSpirulina is severely reduced by exposing the cells to CO2-depletedconditions in the light. The extent of reduction depends onthe length of exposure, the light intensity, and the O2 concentration.The photosynthetic dependence on inorganic carbon (CInorg) concentration,however, is similar at 3% O2 and at 25% O2 but in the presenceof catalase. The amount of O2 released following the additionof catalase to the cell suspension also depends on the O2 andCO2 concentrations. The addition of H2O2 either to the cellsuspension or by a treatment with methyl viologen caused a severeinhibition of the capability of the cells to accumulate inorganiccarbon internally. It is suggested that the reduction of thephotosynthetic apparent affinity to CInorg upon subjecting thecells to photoinhibitory conditions is caused by an alterationof their ability to accumulate CInorg due to the accumulationof H2O2. 相似文献
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Acclimation of stream-bed heterotrophic microflora: metabolic responses to dissolved organic matter 总被引:1,自引:0,他引:1
SUMMARY.
- 1 Studies were performed to assess the acclimation of the stream-bed heterotrophic microflora to sources of dissolved organic matter (DOM) typical of its environment and microfloral responses to pulses of DOM.
- 2 Microcosm measurements of dissolved organic carbon (DOC) uptake, dissolved oxygen uptake. ATP concentration and epitluorescence microscopic counts (EMC) were performed using stream-bed sediments and heterogeneous dissolved organic matter (DOM) sources.
- 3 Three study sites included an undisturbed woodlot spring seep, a small stream traversing a cattle pasture and a larger stream draining a catchment used for silage crops, pastures and woodlands.
- 4 The DOM sources were cold water extracts of forest floor leaf litter, bovine manure, the green alga Ulothrix and jewel weed (Impaliens capensis L.) leaves.
- 5 DOC uptake occurring in 2.5–5.0 h incubations indicated an acclimation of the microflora at each site to DOM sources generated by surrounding land use.
- 6 The sediment microflora from the larger stream did not readily metabolize bovine manure DOM and the latter was used in an acclimation experiment.
- 7 A minimum of 48 h of cumulative exposure to bovine manure DOM at 15–20°C were required to yield measurable changes in sediment microbial activity of sediment microbial biomass.
- 8 The same microflora retained an ability to readily metabolize the added DOM source after 72 h of exposure to unamended stream water.
- 9 The time frame of microfloral responses during acclimation indicated that changes leading to the metabolism of a DOM source were initially enzymatic and eventually involved growth and selection for specific decomposers within the microbial community.
- 10 We conclude that in order to utilize naturally occurring pulses of carbon and energy, stream-bed heterotrophs must be already enzymatically prepared, induced, when the pulse occurs.
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GERALDO L. G. SOARES MARLA A. C. KAPLAN 《Botanical journal of the Linnean Society. Linnean Society of London》2001,135(1):61-66
The flavone-flavolol ratio (fo/fl) for Dicotyledoneae is studied through graphic comparisons between indices indicative of morphological tendencies: the herbaceousness and Sporne indices. These comparisons show a tendency toward the reduction of flavone biosynthesis in arboreous and shrubby taxa. Ligneous families (HI ≤150.0) and morphologically more primitive families (SI ≤55) possess fo/fl <1.OO. However, the relationship between evolutionary status of families with fo/fl values is not simply linear in Dicotyledoneae, because more advanced families are also characterized by a wider range of variation in fo/fl values. 相似文献