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981.
Field studies were conducted during the peak irrigation period(July–August) at the mouth, 50 m upstream and 50 m downstreamoffour irrigation return flows draining a 50 km stretch of theOldmanRiver in the short grass prairie zone of southern Alberta.Watersamples were analyzed weekly. Physico-chemical variableschangesonly slightly at each site but salinity and conductivity weresignificantly higher at the downstream site (Expanse Coulee)andall sites showed an increase over 1978 data. Conductivityalong theleft bank of the river was measured at 50 m intervalsdownstream ofExpanse Coulee until, after 1.5 km, it declined to theupstreamlevel which in the laboratory was shown to require a 660%dilutionof the effluent. In field experiments conducted at ExpanseCouleeit was shown that macroinvertebrate biomass was significantlylowerdownstream of the mouth and significantly higher upstream.Chlorophyll-a was not significantly different betweenthemouth and upstream with both significantly higher thandownstreamwhere it was not detectable. Inorganic carbon assimilation byepilithic algae and heterotrophic potential of the bacteriawereboth significantly higher at the mouth and upstream andsignificantly lower downstream.Organic matter in the sediment was not significantly differentupstream or downstream of the mouth but there was a higherpercentage of large particles (125–250 m) at the mouthanddownstream of EC a higher percentage of medium(60–125 m) andsmall (0–60 m) particles were found 50 m upstream. It isconcluded that at present differences in invertebrate biomass,chlorophyll-a, inorganic carbon assimilation byepilithicalgae and heterotrophic potential of epilithic bacteria atExpanseCoulee are not directly attributable to increase in salinitybutare more probably the result of increased suspended solids andsaltation. 相似文献
982.
We have investigated the regulation of ferredoxin–glutamate synthase (Fd-GOGAT) in leaves of barley (Hordeum vulgare L. cv. Maris Mink) at the mRNA, protein and enzyme activity levels. Studies of the changes in Fd-GOGAT during plant development
showed that the activity in shoots increases rapidly after germination to reach a maximum (on a fresh-weight basis) at day
10 and then declines markedly to less than 50% of the maximal activity by day 30, this decline being correlated with an equivalent
loss of Fd-GOGAT protein. Growing the plants in darkness reduced the maximum activity attained in the shoots, but did not
affect the overall pattern of the changes or their timing. The activity of Fd-GOGAT increased two- to three-fold within 48 h
when etiolated leaves were exposed to light, and Northern blots indicated that the induction occurred at the mRNA level. However,
whilst a carbon source could at least partially substitute for light in the induction of nitrate reductase activity, no induction
of Fd-GOGAT activity was seen when etiolated leaves were treated with either sucrose or glucose. Interestingly, the levels
of Fd-GOGAT mRNA and activity remained high up to a period of 16 h or 72 h darkness, respectively. Compared with plants grown
in N-free medium, light-grown plants supplied with nitrate had almost two-fold higher Fd-GOGAT activities and increased Fd-GOGAT
mRNA levels, but nitrate had no effect on the abundance of the enzyme or its mRNA in etiolated plants, indicating that light
is required for nitrate induction of barley Fd-GOGAT.
Received: 23 April 1997 / Accepted: 28 May 1997 相似文献
983.
Combined effects of elevated CO2 and air temperature on carbon assimilation of Pinus taeda trees 总被引:1,自引:1,他引:0
R. O. TESKEY 《Plant, cell & environment》1997,20(3):373-380
Branches of 22-year-old loblolly pine (Pinus taeda, L.) trees growing in a plantation were exposed to ambient CO2, ambient + 165 μmol mol?1 CO2 or ambient + 330 μmol mol?1 CO2 concentrations in combination with ambient or ambient + 2°C air temperatures for 3 years. Field measurements in the third year indicated that net carbon assimilation was enhanced in the elevated CO2 treatments in all seasons. On the basis of A/Ci, curves, there was no indication of photosynthetic down-regulation. Branch growth and leaf area also increased significantly in the elevated CO2 treatments. The imposed 2°C increase in air temperature only had slight effects on net assimilation and growth. Compared with the ambient CO2 treatment, rates of net assimilation were ~1·6 times greater in the ambient + 165 μmol mol?1 CO2 treatment and 2·2 times greater in the ambient + 330 μmol mol?1 CO2 treatment. These ratios did not change appreciably in measurements made in all four seasons even though mean ambient air temperatures during the measurement periods ranged from 12·6 to 28·2°C. This indicated that the effect of elevated CO2 concentrations on net assimilation under field conditions was primarily additive. The results also indicated that the effect of elevated CO2 (+ 165 or + 330 μmol mol?1) was much greater than the effect of a 2°C increase in air temperature on net assimilation and growth in this species. 相似文献
984.
Identification of an assimilatory nitrate reductase in mutants of Paracoccus denitrificans GB17 deficient in nitrate respiration 总被引:2,自引:0,他引:2
Heather J. Sears Phillip J. Little D. J. Richardson B. C. Berks Stephen Spiro Stuart J. Ferguson 《Archives of microbiology》1997,167(1):61-66
A Paracoccus denitrificans strain (M6Ω) unable to use nitrate as a terminal electron acceptor was constructed by insertional inactivation of the periplasmic
and membrane-bound nitrate reductases. The mutant strain was able to grow aerobically with nitrate as the sole nitrogen source.
It also grew anaerobically with nitrate as sole nitrogen source when nitrous oxide was provided as a respiratory electron
acceptor. These growth characteristics are attributed to the presence of a third, assimilatory nitrate reductase. Nitrate
reductase activity was detectable in intact cells and soluble fractions using nonphysiological electron donors. The enzyme
activity was not detectable when ammonium was included in the growth medium. The results provide an unequivocal demonstration
that P. denitrificans can express an assimilatory nitrate reductase in addition to the well-characterised periplasmic and membrane-bound nitrate
reductases.
Received: 12 August 1996 / Accepted: 29 October 1996 相似文献
985.
J. D. BARNES T. PFIRRMANN K. STEINER C. LÜTZ U. BUSCH H. KÜCHENHOFF H.-D. PAYER 《Plant, cell & environment》1995,18(12):1345-1457
Two clones of 5-year-old Norway spruce [Picea abies (L.) Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750 μmol mol?1) and O3 (20 and 75nmolmol?1) in a phytotron at the GSF-Forschung-szentrum (Munich) over the course of a single season (April to October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian Forest, and trees were grown in large containers of forest soil fertilized to achieve contrasting levels of potassium nutrition, designated well-fertilized or K-deficient. Measurements of the rate of net CO2 assimilation were made on individual needle year age classes over the course of the season, chlorophyll fluorescence kinetics were recorded after approximately 23 weeks, and seasonal changes in non-structural carbohydrate composition of the current year's foliage were monitored. Ozone was found to have contrasting effects on the rate of net CO2 assimilation in different needle age classes. After c. 5 months of fumigation, elevated O3 increased (by 33%) the rate of photosynthesis in the current year's needles. However, O3 depressed (by 30%) the photo-synthetic rate of the previous year's needles throughout the period of exposure. Chlorophyll fluorescence measurements indicated that changes in photosystem II electron transport played no significant role in the effects of O3 on photosynthesis. The reasons for the contrasting effects of O3 on needles of different ages are discussed in the light of other recent findings. Although O3 enhanced the rate at which CO2 was fixed in the current year's foliage, this was not reflected in increases in the non-structural carbohydrate content of the needles. The transfer of ambient CO2-grown trees to a CO2-enriched atmosphere resulted in marked stimulation in the photosynthetic rate of current and previous year's foliage. However, following expansion of the current year's growth, the photosynthetic rate of the previous year's foliage declined. The extent of photosynthetic adjustment in response to prolonged exposure to elevated CO2 depended upon the clone, providing evidence of intraspecific variation in the long-term response of photosynthesis to elevated CO2. The increase in photosynthesis induced by CO2 enrichment was associated with increased foliar concentrations of glucose, fructose and starch (but no change in sucrose) in the new growth. CO2 enrichment significantly enhanced the photosynthetic rate of K-deficient needles, but there was a strong CO2soil interaction in the current year's needles, indicating that the long-term response of trees to a high CO2 environment may depend on soil fertility. Although the rate of photosynthesis and non-structural carbohydrate content of the new needles were increased in O3-treated plants grown at higher levels of CO2, there was no evidence that elevated CO2 provided additional protection against O3 damage. Simultaneous exposure to elevated O3 modified the effects of elevated CO2 on needle photosynthesis and non-structural carbohydrate content, emphasizing the need to take into account not only soil nutrient status but also the impact of concurrent increases in photochemical oxidant pollution in any serious consideration of the effects of climate change on plant production. 相似文献
986.
A field study of the effects of elevated CO2 on carbon assimilation, stomatal conductance and leaf and branch growth of Pinus taeda trees 总被引:4,自引:3,他引:1
R. O. TESKEY 《Plant, cell & environment》1995,18(5):565-573
A study was conducted in 21-year-old loblolly pine (Pinus taeda L.) trees growing in plantation in north central Georgia, USA. The experiment used branch chambers to impose treatments of ambient, ambient +165 and ambient + 330 μmol mol?1 CO2. After one growing season there was no indication of acclimation to elevated CO2. In August and September, carbon assimilation, measured by two different methods, was twice as high at ambient +330 μmol mol?1 CO2 than at ambient. Dark respiration was suppressed by 6% at ambient +165 and by 14% at ambient + 330 μmol mol?1 CO2. This suppression was immediate, and not an effect of exposure to elevated CO2 during growth, since respiration was reduced by the same amount in all treatments when measured at a high CO2 concentration. Elevated CO2 increased the growth of foliage and woody tissue. It also increased instantaneous transpiration efficiency, but it had no effect on stomatal conductance. Since the soil at the study site had low to moderate fertility, these results suggest that the growth potential of forests on many sites may be enhanced by global increases in atmospheric CO2, concentration. 相似文献
987.
G. W. McCarty 《Plant and Soil》1995,170(1):141-147
Recent advances in our understanding of the enzymology and regulatory systems involved in microbial metabolism of N hold promise to elucidate some of the underlying factors controlling metabolism of N in soil ecosystems. A review of recent work is used to construct a paradigm for N metabolism regulation in soil based on the central role of glutamine synthetase (GS) in such regulation within the soil microbial community. The studies involved use of GS inhibitors to elucidate the role of GS activity in regulation of soil N metabolism. Such studies have shown that the glutamine formed by microbial assimilation of NH4
+ via GS activity influences the regulatory mechanisms controlling both the production and activity of enzymes involved in N metabolism. For example, these studies showed that the inhibition of GS activity within the soil microbial community relieved the repression of urease production caused by microbial assimilation of inorganic N and blocked the short-term regulation of assimilatory nitrate reductase (ANR) by NH4
+ assimilation. Other studies have indicated that common environmental factors in soil may influence GS activity in microorganisms and thereby may influence metabolism of N within the soil microbial community. The paradigm for N metabolism regulation in soil that has emerged from such studies should lead to a better understanding of the mechanisms controlling fate of N in soil ecosystems. 相似文献
988.
Prashant S. Phale Handanahal S. Savithri N. Appaji Rao Chelakara S. Vaidyanathan 《Archives of microbiology》1995,163(6):424-431
Pseudomonas maltophilia CSV89, a soil bacterium, produces an extracellular biosurfactant, Biosur-Pm. The partially purified product is nondialyzable and chemically composed of 50% protein and 12–15% sugar, which indicates the complex nature of Biosur-Pm. It reduces the surface tension of water from 73 to 53×10-3 N m-1 and has a critical micellar concentration of 80 mg/l. Compared to aliphatic hydrocarbons, Biosur-Pm shows good activity against aromatic hydrocarbons. The emulsion formed is stable and does not require any metal ions for emulsification. The kinetics of Biosur-Pm production suggest that its synthesis is a growth-associated and pH-dependent process. At pH 7.0, cells produced more Biosur-Pm with less cell surface hydrophobicity. At pH 8.0, however, the cells produced less Biosur-Pm with more cell surface hydrophobicity and showed a twofold higher affinity for aromatic hydrocarbons compared to the cells grown at pH 7.0. The Biosur-Pm showed a pH-dependent release, stimulated growth of the producer strain on mineral salts medium with 1-naphthoic acid when added externally, and facilitated the conversion of salicylate to catechol. All these results suggest that Biosur-Pm is probably a cell-wall component and helps in hydrocarbon assimilation/uptake. 相似文献
989.
In the facultative chemoautotroph Alcaligenes eutrophus H16, most of the genes (cbb genes) encoding enzymes of the Calvin carbon reduction cycle are organized within two highly homologous cbb operons, one located on the chromosome and the other on the megaplasmid pHG1. Nucleotide sequencing of the promoter-distal part of the operons revealed three open reading frames, designated cbbG, cbbK, and cbbA. Similarity searches in databases and heterologous expressions of the subcloned genes in Escherichia coli identified them as genes encoding the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, and a class II fructose-1,6-bisphosphate aldolase, respectively. The aldolase could be grouped together with the enzymes from Rhodobacter sphaeroides and Bacillus subtilis as a new subtype of class II aldolases. A phenotypic complementation analysis with a cbb operon mutant of A. eutrophus showed that the cbbG product is essential for autotrophic growth of the organism, whereas the products of cbbK and cbbA can apparently be substituted by isoenzymes encoded elsewhere on the chromosome. No or only low constitutive promoter activity was associated with cbbK and cbbA, respectively, confirming the two genes as parts of the cbb operon. Downstream of cbbA, the very high overall nucleotide sequence identity (about 94%) prevailing throughout the two cbb operons discontinues, suggesting that cbbA is the most promoter-distal gene of the operon.Abbreviations
FBA
Fructose 1,6-bisphosphate aldolase
-
GAPDH
Glyceraldehyde-3-phosphate dehydrogenase
-
PRK
Phosphoribulokinase
-
RubisCO
Ribulose-1,5-bisphosphate carboxylase/oxygenase 相似文献
990.
Long term water stress inactivates Rubisco in subterranean clover 总被引:11,自引:0,他引:11
In long-term field experiments, during consecutive years, microswards of subterranean clover were irrigated to minimise water deficits or subjected to progressively increasing drought over 30 days. Both leaf water potential and relative water content steadily decreased during the experiments. Plants affected by drought grew more slowly and photosynthesis was decreased. Photosynthetic rate (A) and Rubisco were analysed in relation to midday water potentials and relative water contents. The difference in A between draughted and irrigated plants increased progressively, in part as a result of decreased stomatal conductance and CO2 concentration within leaf (Ci). However, A-Ci curves suggest that the photosynthetic capacity in plants experiencing long-term stress was reduced by 50% when compared with irrigated plants. Drought decreased both the initial and the total Rubisco activity per unit area in a similar way but did not reduce the amount of Rubisco protein per unit leaf area. Thus, the specific activity of Rubisco, rather than its activation state, decreased suggesting that under water stress the active sites were blocked by inhibitors. 相似文献