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61.
Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures
of O2 (pO2; 1–80%, v/v, in N2) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO2 tested. In sub-ambient pO2 (1 and 2.5%) nodules contained specific activities of uricase (urate: O2 oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those
from air. On a cell basis, uninfected cells in nodules from 1% O2 contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in
sub-ambient O2, the activities of other enzymes of ureide synthesis were relatively unaffected by pO2. Short-term effects of pO2 on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO2 (1, 2.5 or 5%, v/v in N2) and15N2. Despite a fall in total15N2 fixation, ureide synthesis and export was maintained at a high level except in 1% O2 where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules
which allow the balance between O2 supply and demand to be maintained over a wide range of pO2, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of
fixed nitrogen.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance
Bureau postgraduate fellowship (to F.D.D.). 相似文献
62.
Determination of the pressure in the water-conducting vessels of intactNicotiana rustica L. plants showed that the pressure probe technique gave less-negative values than the Scholander-bomb method. Even though
absolute values of the order of −0.1 MPa could be directly recorded in the xylem by means of the pressure probe, pressures
between zero and atmospheric were also frequently found. The data obtained by the pressure probe for excised leaves showed
that the Scholander bomb apparently did not read the actual tension in the xylem vessles ofNicotiana plants. The possibility that the pressure probe gave false readings was excluded by several experimental controls. In addition,
cavitation and leaks either during the insertion of the microcapillary of the pressure probe, or else during the measurements
were easily recognized when they occurred because of the sudden increase of the absolute xylem tension to that of water vapour
or to atmospheric, respectively. Tension values of the same order could also be measured by means of the pressure probe in
the xylem vessels of pieces of stem cut from leaves and roots under water and clamped at both ends. The magnitude of the absolute
tension depended on the osmolarity of the bathing solution which was adjusted by addition of appropriate concentrations of
polyethylene glycol. Partial and uniform pressurisation of plant tissues or organs, or of entire plants (by means of the Scholander
bomb or of a hyperbaric chamber, respectively) and simultaneous recording of the xylem tension using the pressure probe showed
that a 1∶1 response in xylem pressure only occurred under a few circumstances. A 1∶1 response required that the xylem vessels
were in direct contact with an external water reservoir and/or that the tissue was (pre-)infiltrated with water. Corresponding
pressure-probe measurements in isolated vascular bundles ofPlantago major L. orP. lanceolata L. plants attached to a Hepp-type osmometer indicated that the magnitude of the tension in the xylem vessels was determined
by the external osmotic pressure of the reservoir. These and other experiments, as well as analysis of the data using classical
thermodynamics, indicated that the turgor and the internal osmotic pressure of the accessory cells along the xylem vessels
play an important role in the maintenance of a constant xylem tension. This conclusion is consistent with the cohesion theory.
In agreement with the literature (P.E. Weatherley, 1976, Philos. Trans. R. Soc. London Ser. B23, 435–444; 1982, Encyclopedia of plant physiology, vol. 12B, 79-109), it was found that the tension in the xylem of intact
plants under normal and elevated ambient pressure (as measured with the pressure probe) under quasi-stationary conditions
was independent of the transpiration rate over a large range, indicating that the conductance of the flow path must be flow-dependent. 相似文献
63.
The loading of amino acids and nitrate into the xylem was investigated by collection and analysis of root-pressure exudate from the cut hypocotyl stumps of seedlings of Ricinus communis L. Glutamine was found to be the dominant amino acid in the exudate and also to be the amino acid which is transferred to the xylem most rapidly and accumulated to the greatest extent. The comparison between uptake and xylem loading showed significant differences in specificity between these two transport reactions, indicating a different set of transport systems. Nitrate is transferred to the xylem at a higher relative rate than any amino acid despite the great nitrate-storage capacity of the root system. Thus the supply of nitrate to Ricinus plants leads to enhanced nitrogen allocation to the shoots. 相似文献
64.
Nodules of cowpea (Vigna unguiculata (L.) Walp. cv. Vita 3:Bradyrhizobium CB 756) from 28-d-old plants cultured for 23 d with their root systems maintained in O2 levels from 1 to 80% (v/v, in N2) in the external gas phase showed a range of structural changes which have been interpreted in relation to an over- or under-supply
of O2. A response to the partial pressure of O2 in the gas phase (pO2) was noted with respect to nodule size, lenticel development, the relative distributions of cortical and infected central
tissue, the differentiation of cortex, especially the inner cortex, the frequency and size of infected and uninfected interstitial
cells, the volume of extracellular spaces both in cortex and infected tissue, and in the frequency of bacteroids. As a consequence
of these changes the surface area of inner cortex relative to the nitrogenase-containing units of fixing tissue (infected
cells or bacteroids) was increased by as much as 20-fold. Effectiveness of bacteroid functioning increased from 0.10 ± 0.02
· 10-9 μmol acetylene reduced per bacteroid in air-grown nodules to 0.9 ± 0.16 · 10-9 (same units) per bacteroid in those cultured in 1% O2.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian International Development
Assistance Bureau postgraduate fellowship (to F.D.D.). The authors wish to thank Dr. W.F.C. Blumer for his considerable help
with morphometric analysis, Dr. J. Kuo for guidance in the use of histological techniques, and to Dr. J.S. Pate for the suggestion
that lenticel development might be quantified by surface staining of nodules. 相似文献
65.
66.
Two monobiotinylated analogs of neuropeptide Y (NPY) were synthesized by coupling the N-hydroxysuccinimidyl esters of biotin and (6-biotinylamido)-hexanoic acid, respectively, to the free alpha-NH2 group of the side chain protected NPY peptide resin. Crude peptides obtained by HF cleavage were purified by RPLC and their integrities were confirmed by amino acid and mass spectral analysis. As with NPY, both biotinylated analogs inhibited 125I-NPY binding and adenylate cyclase activity of rat cardiac ventricular membranes in a dose-dependent manner. N-alpha-[(6-biotinylamido)-hexanoyl]-NPY exhibited potencies comparable to that of NPY whereas N-alpha-biotinyl-NPY was slightly less potent. In the in vivo experiments, however, both the biotinylated analogs exhibited responses comparable to NPY in increasing arterial blood pressure and decreasing heart rate in anesthetized rats. The responses of the biotinyl analogs were longer lasting than those of NPY. Histochemical studies revealed that N-alpha-[(6-biotinylamido)-hexanoyl]-NPY could label the NPY receptors in rat cardiac ventricular tissues. This labeling was specific since intact NPY inhibited the staining. These studies show that biotinyl-NPY analogs exhibit biological potencies comparable to intact NPY and can therefore be used to further probe the NPY-receptor interaction. 相似文献
67.
将乙酰胆碱(ACh)注入麻醉家兔脊髓蛛网膜下腔,观察其对心血管活动的影响。结果表明:(1)脊髓蛛网膜下腔注射50~100μg ACh可使血压下降,心率减慢;(2)预先由脊髓蛛网膜下腔注射阿托品,可阻断ACh引起的降压和降心率作用;(3)脊髓蛛网膜下腔注射六甲双铵、酚妥拉明或心得安均不能阻断上述ACh的心血管反应;(4)切断两侧颈部迷走神经,ACh不再使心率减慢,但其降低血压的作用不受到任何影响。 脊髓中ACh水平升高可通过激活胆碱能M-受体引起血压下降和心率减慢。ACh的这种降压作用既没有中枢肾上腺素能受体活动参与,也不是通过迷走神经实现的,可能是由于脊髓交感血管中枢紧张性降低所造成的。 相似文献
68.
V. G. Sideleva 《Journal of fish biology》1996,49(SA):192-206
Lake Baikal's 29 endemic species of cottoid fishes form three groups: shallow-water species in depths to 350 m; eurybathic species from 50 to 1300 m; and abyssal species from 400 to 1600 m. These groups differ in their abilities to withstand high hydrostatic pressure. As in marine deep-water fishes, abyssal cottoids in Baikal have few or no cones in the retina, and some have tubular eyes. Their seismosensory systems predominate, based chiefly on free neuromasts. The proportion of species with canal systems decreases with depth. Diversity of the predominantly gammarid foods also decreases from 45 species in shallow water to five species in deep water, and the lateral line system plays the dominant role in food detection at all depths. Two abyssal cottoids have become secondary pelagic, achieving close to neutral buoyancy through high lipid levels and reduced skeletal mineralization. These forms take advantage of the abundant pelagic planktonic amphipod populations. The adaptations of abyssal forms parallel those seen in deep-water marine fishes. 相似文献
69.
David R. Thompson Jurgen E. Pohl Yiu-Yu S. Tse Robert W. Hiorns 《International journal of biometeorology》1996,39(3):116-120
Analysis of the time of onset of chest pain in 2254 patients with a myocardial infarction admitted to a coronary care unit in Leicester during a 10-year period shows an association with temperature and humidity. During both the most cold and humid times of the year, the relationship is a strong one. A generalized linear model with a log link was used to fit the data and the backward elimination selection procedure suggested a humid, cold day might help to trigger the occurrence of myocardial infarction. In addition, cold weather was found to have a stronger effect on the male population while those men aged between 50 and 70 years were more sensitive to the effect of high humidity. 相似文献
70.
心率与血压的变异性:分析方法,生理意义及其应用 总被引:19,自引:0,他引:19
本文回顾了关心回顾变异性及血压变异性的最新进展。在分析方法方面介绍了单一生理变量多变量系统的线性分析技术及其主要结果。对HRV/BPV谱的生理意义及其应用问题,也进行了回顾了评述。 相似文献