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71.
Fabrizio Arigoni P. Alexandre Kaminski Hauke Hennecke Claudine Elmerich 《Molecular & general genetics : MGG》1991,225(3):514-520
Summary The nucleotide sequence of a 4.1 kb DNA fragment containing the fixABC region of Azorhizobium caulinodans was established. The three gene products were very similar to the corresponding polypeptides of Rhizobium meliloti. The C-terminal domains of both fixB products displayed a high degree of similarity with the -subunits of rat and human electron transfer flavoproteins, suggesting a role for the FixB protein in a redox reaction. Two open reading frames (ORF) were found downstream of fixC. The first ORF was identified as fixX on the basis of sequence homology with fixX from several Rhizobium and Bradyrhizobium strains. The second ORF potentially encoded a 69 amino acid product and was found to be homologous to a DNA region in the Rhodobacter capsulatus nif cluster I. Insertion mutagenesis of the A. caulinodans fixX gene conferred a Nif– phenotype to bacteria grown in the free-living state and a Fix– phenotype in symbiotic association with the host plant Sesbania rostrata. A crude extract from the fixX mutant had no nitrogenase activity. Furthermore, data presented in this paper also indicate that the previously identified nifO gene located upstream of fixA was probably a homologue of the nifW gene of Klebsiella pneumoniae and Azotobacter vinelandii. 相似文献
72.
Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria 总被引:4,自引:0,他引:4
Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The 13C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (13C between-25.3 and-27.8) were significantly less depleted in 13C than needles (13C between-27.3 and-29.1), and 13C in twigs increased consistently with age. The 15N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles 15N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in 15N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. 15N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. 15N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The 15N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed. 相似文献
73.
Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH
inf4
sup+
uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent Km but did not significantly affect Vmax (mean Vmax=4.23±1.97 mole·g–1·h–1). The apparent Km increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH
inf4
sup+
uptake in S. alterniflora. No significant NH
inf4
sup+
uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both Vmax and Km. Reduction of solution salinity from 35 to 5 g/L did not change Vmax but reduced Km by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in Vmax of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH
inf4
sup+
. For both experiments, increasing salinity led to an increase in the apparent Km similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH
inf4
sup+
uptake kinetics. 相似文献
74.
Nitrate nutrition ofDeschampsia flexuosa (L.) Trin. in relation to nitrogen deposition in Sweden 总被引:1,自引:0,他引:1
Summary Current and maximally induced nitrate reductase activity (NRA), total-N, nitrate, K, P, Ca, Mg, Mo and sucrose in leaves ofDeschampsia flexuosa was measured three times during the vegetation period in forests along a deposition gradient (150 km) in south Sweden, in
north Sweden where the nitrogen deposition is considerably lower, and at heavily N-fertilized plots. In addition, the interaction
between nitrogen nutrition and light was studied along transects from clearings into forest in both south and north Sweden.
Plants from sites with high nitrogen deposition had elevated current NRA compared to plants from less polluted sites, indicating
high levels of available soil nitrate at the former. Current NRA and total N concentration in grass from sites with high deposition
resembled those found at heavily N-fertilized plots. Under such circumstances, the ratio current NRA: maximally induced NRA
as well as the concentration of nitrate was high, while the concentration of sucrose was low. This suggests that the grass
at these sites was already utilizing a large portion of its capacity to assimilate nitrate. Light was found to play an important
role in the assimilation of nitrate; leaf concentration of sucrose was found to be negatively correlated with both nitrate
and total N. Consequently, grass growing under dense canopies in south Sweden is not able to dilute N by increasing growth.
The diminished capacity of the grass to assimilate nitrate will increase leaching losses of N from forests approaching N saturation. 相似文献
75.
Summary Plants of Drosera species, neighbouring noncarnivorous plants, and arthropods on or near each Drosera sp. were collected at 11 contrasting habitat locations in SW Australia. At three of the sites clones of the rare glandless mutant form of D. erythrorhiza were collected alongside fully glandular counterparts. The 15N value (15N/14N natural isotope composition) of insect-free leaf and stem fractions was measured, and the data then used to estimate proportional dependence on insect N (%NdI) for the respective species and growth forms of Drosera. The data indicated lower %NdI values for rosette than for self-supporting erect or for climbing vine species. The latter two groups showed an average %NdI value close to 50%. The %NdI increased with length and biomass of climbing but not erect forms of Drosera. 15N values of stems were positively correlated with corresponding values for leaves of Drosera. Leaf material was on average significantly more 15N enriched than stems, possibly due to delayed transport of recent insect-derived N, or to discrimination against 15N in transfer from leaf to the rest of the plant. The comparison of 15N values of insects and arthropod prey, glandless and glandular plants of D. erythrorhiza indicated %NdI values of 14.3, 12.2 and 32.2 at the respective sites, while matching comparisons based on 15N of insect, reference plants and glandular plants proved less definitive, with only one site recording a positive %NdI (value of 10.4%) despite evidence at all sites of feeding on insects by the glandular plants. The use of the 15N technique for studying nutrition of carnivorous species and the ecological significance of insect feeding of different growth forms of Drosera growing in a large range of habitats is discussed. 相似文献
76.
77.
78.
J. E. Irvine G. T. A. Benda B. L. Legendre G. R. Machado Jr 《Plant Cell, Tissue and Organ Culture》1991,26(2):115-125
This study investigates the frequency of apparent and permanent expression of marker change following two types of tissue culture, conventional callus and direct regeneration cultures, and for two markers it relates this frequency to that following breeding. Each clone was used for only one marker. After conventional callus culture, plants of the sugarcane clone Arundoid B, a clone having a growth habit with shortened internodes and leaves, were freed of this marker at a rate of 1 in 172 plants. Marker remission in a second clone with a leaf blotch was enhanced in the presence of a mutagen. Callus culture alone gave a remission rate of 1/280 plants, while treatment of callus with ethyl methanesulfonate gave a remission rate of 1/42 plants. Of two markers subjected to vegetative and sexual transmission, the first, a leaf marker, was stable in callus culture with no remissions; crossing with non-marker parents produced progeny with 54% lacking the marker. The second, a stalk marker (multibud), showed epigenetic effects during two generations of vegetative propagation; plants lacking the multibud marker produced vegetative progeny in which the marker reappeared. Nine crosses to nonmarker parents produced progeny of which an average of 29% had the marker. The use of stalk chimeras as markers demonstrated that passage through conventional callus or direct regeneration culture resulted in the loss of the donor phenotype in all plants regenerated. Phenotypic variation in plants derived from callus culture appears to arise from several sources; chimeral segregants, epigenetic transients, and mutational variants. 相似文献
79.
森林土壤氮转化的微生物功能研究 总被引:2,自引:1,他引:1
本文研究了不同林型下土壤(A+6层和A_1层)微生物、土壤酶活性在森林土壤氮转化中的作用。结果表明不同林型下土壤具有不同的固氮作用、反硝化作用、氨化作用和硝化作用速率,即阔叶林>针阔混交林>针叶林。已经证明,固氮作用主要存在于森林土壤的A_1层,反硝化作用主要存在于A_0层。森林土壤存在2种硝化作用过程,即由自养微生物所引起的自养硝化作用过程和异养微生物所引起的异养硝化作用过程。它的存在与林型有关,某些森林土壤中这2种硝化作用过程都存在,如针阔混交林下的A_0层和A_1层。有些林型下土壤,则以异养硝化作用过程为主,如针叶林的A_0层。 相似文献
80.
Gerd Wallukat Gyorgy Nemecz Tibor Farkas Hartmut Kuehn Albert Wollenberger 《Molecular and cellular biochemistry》1991,102(1):35-47
Incubation of rocker-cultured neonatal rat heart cells with 3 mM L(+)-lactate led to a sharp increase in the sensitivity of cardiomyocytes to the beta-adrenergic agonist isoprenaline, as measured by their chronotropic response. This effect was accompanied by a reduction in the arachidonic acid content of the total phospholipids. The phospholipase A2-activator melittin as well as free arachidonic acid induced this supersensitivity to the same degree. On the other hand, the L(+)-lactate-evoked supersensitivity could be blocked by the phospholipase A2 inhibitors mepacrine and n-bromophenacyl-bromide, suggesting an involvement of phospholipase A2 in the process of beta-adrenergic sensitization. The sensitizing action of arachidonic acid was blocked by the lipoxygenase inhibitors esculetin and nordihydroguaiaretic acid, but not by the cyclooxygenase inhibitor indomethacin. Supersensitivity was likewise evoked by 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), but not by 5-S-HPETE or 5-S-HETE. These findings suggest that the phospholipase A2-15-lipoxygenase pathway plays a role in the induction of beta-adrenergic supersensitivity in the cultured cardiomyocytes and point to a new physiological role of the lipoxygenase product 15-S-HETE.Abbreviations NDGA
nordihydroguaiaretic acid
- HETE
hydroeicosatetraenoic acid
- HPETE
hydroperoxyeicosatetraenoic acid 相似文献