Growth of Nitrobacter by dissimilatoric nitrate reduction

Abstract Eight strains of the genus Nitrobacter grew under anaerobic conditions in the presence of nitrate. The growth was inhibited by nitrate concentrations above 0.5 mM. By a special culture technique inhibition caused by nitrite was abolished. Nitrate oxidizing cells grew in gas tight culture flasks as a biofilm on a gas-permeable silicone tubing. The biofilm allowed nitrate-reducing cells to grow at a low nitrite concentration. These cells grew either actively motile in the anaerobic medium, or in anaerobic zones of the biofilm. They produced nitrite and ammonia. Nitrogen balance calculations established a loss of inorganic nitrogen for 5 of 8 strains. This implies that nitrate-reducing cells produced furthermore volatile nitrogen compounds. N₂O was detected by gas chromatography.     

利他林对戊巴比妥钠深麻醉家兔呼吸的兴奋效应及机制

在125只呼吸受戊巴比妥钠抑制并切断双侧颈迷走神经的家兔,分析了利他林(MP)呼吸效应的中枢部位及可能的递质。静脉注射 MP(2mg/kg)引起呼气时程显著缩短和呼吸频率显著增加。去除颈动脉体不影响 MP 兴奋呼吸的效应。将浸有2%MP 溶液的滤纸(2×2mm~2)贴敷在第四脑室底闩附近,或微量注射2%MP 2μl 到延髓 NTS 区,均可引起上述效应,但 NA区、NPBM 区和皮层体感运动区则无效。第四脑室或 NTS 区微量注射酚妥拉明均可阻断 MP兴奋呼吸的效应,但第四脑室注射心得安却不能阻断。结果提示,MP 可能作用于 NTS 区,在肾上腺素能α受体的参与下,受戊巴比妥钠抑制的家兔发生呼吸频率增快的效应。     

No evidence for a pleiotropic relationship between male sterility and cyanide-resistant respiration in Plantago lanceolata

Gynodioecy, the coexistence of hermaphrodites and male steriles, is frequent in populations of Plantago lanceolata L. A condition for the maintenance of gynodioecy in an obligatory outbreeding species like this is an increase in female fitness in male steriles compared with hermaphrodites. One of the possible underlying mechanisms, a lower cyanide-resistant respiration in male steriles, which could lead to a higher metabolic efficiency, was investigated. For the experiments adult plants were used, because the effects which compensate for male sterility have been found in characters like seed production and longevity. No general correlation between sex phenotype and cyanide-resistant respiration capacity, or with any other respiration component, was found. Only in a single cross a strong correlation between cyanide-resistant respiration activity and sex phenotype was established, male steriles possessing the higher activity. The conclusion from these experiments is that there is no pleiotropic relationship between respiration levels and sex phenotype. The strongly significant correlation mentioned is ascribed to chromosomal linkage.     

The response of stomata to CO2 relates to its effect on respiration and ATP level

External ATP enhanced stomatal opening of Commelina communis L. differently from EDTA. ATP was more effective in opening stomata than EDTA, when both were applied in amounts yielding equivalent free Ca²⁺ concentration. The stimulation by ATP depended upon its de-phosphorylation and was not due to the P₁ released. Hence an energetical contribution of external ATP appears possible. Increase in CO₂ concentration increased the stimulation of stomatal opening by ATP and diminished the internal ATP level, ATP/(ADP+AMP) ratio and respiration rate.     

The effect of excitation on the rate of respiration in the liverwort Conocephalum conicum

Simultaneous measurements were taken of the electrical activity and the rate of respiration of thalli of Conocephalum conicum L. stimulated electrically and mechanically (by cutting). The measurements of the rate of respiration employed a modified Warburg apparatus for O₂ consumption and an infra-red gas analyzer with computer recording and data processing for CO₂ evolution. The action potential, produced by either a cut (a damaging stimulus) or an electrical stimulus (a non-damaging stimulus), caused a transient rise in the rate of respiration. The course of changes in the rate of respiration depends on the character of the excitation and the area of the thallus covered by it. If stimulation does not produce excitation, the increase in the rate of respiration does not take place, regardless of the magnitude and type of the stimulus applied.     

Growth and respiration in two mangrove species at a range of salinities

Growth and dark respiration rates were measured in leaves and roots of seedlings of Avicennia marina (Forsk.) Vierh, (grey mangrove), and Aegiceras corniculatum (L.) Blanco (river mangrove). Plants were grown in a soil mixture at ambient temperatures and watered with 0.25 and 100% sea-water. Oxygen uptake was measured in excised root and leaf samples. In both species growth was maximal in 25% sea-water, and root respiration was lowest in 100% sea-water. Differences were found between the two species in the responses of leaf respiration to salinity. In A. corniculatum leaf respiration was raised in both 25 and 100% sea-water, while in A. marina only leaves in 100% sea-water showed higher rates of respiration. These results are consistent with the view that A. marina is the more salt-tolerant of the two species. In A. corniculatum the respiration rates of the hypocotyl were also measured, and were much higher in 100% sea-water than in the other two treatments. The results suggest that at high salinities there is a high metabolic cost in the shoots of both species, and that at such salinities rates of root respiration may be limited by the supply of substrate from the shoots.     

Drought resistance and root morphology in sorghum

Two 2 m³ plots of soil were prepared to different water contents and each isolated from surrounding soil by impermeable plastic material. Nine sorghum varieties were germinated in the plots and allowed to grow without further watering. Time-to-wilt after emergence was measured, and several parameters relating to water flow of the seedling and nodal roots were determined. There was a good positive correlation between both seminal root and nodal root relative conductvity and time-to-wilt. In a second experiment, plants were germinated and grown in pots, and after two weeks of growth without further watering were inspected for survival in the unwilted state. The per cent survival was calculated. There was a negative correlation of seminal root relative conductivity with per cent survival, and a high negative correlation of the number of seminal roots with per cent survival. It is concluded that high relative conductivity indicates drought resistance if the plants are growing with less restricted roots as in open soil, while if the plants are grown in pots the reverse is the case. Experiments linking root conductivity with survival conducted in pots are poor predictors of performance in less restricted rooting conditions.     

Evidence for a periodic excretion of nitrogen by roots of grass-legume associations

Diurnal variation in ion content of the solution bathing roots of two plants growing together in sand culture was analysed for three pairs of grass-legume species (Lolium multiflorum andTrifolium pratense; Zea mays andGlycine hispida; Avena sativa andVicia sativa) and their monospecific controls. Biomass and nitrogen content of plants were determined. Ion concentration (NO ₃ ⁻ , NO ₂ ⁻ , NH ₄ ⁺ , and K⁺) and pH of root solutions were measured for Lolium-Trifolium plant pairs and controls at 6 hours intervals over 36 h, starting at 8 am within a circadian cycle. Root solutions were regularly depleted in NO ₃ ⁻ by the grasses (Lolium-Lolium control) throughout the cycle. For associations involving the legume (Lolium-Trifolium and Trifolium-Trifolium), NO ₃ ⁻ depletion was followed by NO ₃ ⁻ enrichment at night, from late afternoon to early morning; the enrichment was more marked for the Lolium-Trifolium association. Solutions which did not contain NO ₂ ⁻ ions, were enriched by trace amounts of NH ₄ ⁺ ions, largely depleted in K⁺ and alkalanized for all associations throughout the cycle. Repeating the experiment with the three pairs of species at the vegetative phase of development confirmed the previous results: NO ₃ ⁻ enrichment during the night for associations with legumes. When the experiment was repeated with older plants which had almost completed their flowering stage, depletion only was observed and no NO ₃ ⁻ enrichment. These data suggest that NO ₃ ⁻ enrichment results from N excretion from active nodulated roots of the legume, accounting for the increase in both biomass and nitrogen content of the companion grass in grass-legume association. The quantitative importance and periodicity of nitrogen excretion as well as the origin of nitrate enrichment are discussed.     

Radial transport of water across cortical sleeves of excised roots ofZea mays L.

The stationary radial volume flows across maize (Zea mays L.) root segments without steles (sleeves) were measured under isobaric conditions. The driving force of the volume flow is an osmotic difference between the internal and external compartment of the root preparations. It is generated by differences in the concentrations of sucrose, raffinose or polyethylene glycol. The flows are linear functions of the corresponding osmotic differences ( ) up to osmotic values which cause plasmolysis. The straight lines obtained pass through the origin. No asymmetry of the osmotic barrier could be detected within the range of driving forces applied ( =±0.5 MPa), corresponding to volume-flow densities of j_{v, s}=±7·10^–8 m·s^–1. Using the literature values for the reflection coefficients of sucrose and polyethylene glycol in intact roots (E. Steudle et al. (1987) Plant Physiol.84, 1220–1234), values for the sleeve hydraulic conductivity of about 1·10^–7 m·s^–1 MPa^–1 were calculated. They are of the same order of magnitude as those reported in the literature for the hydraulic conductivity of intact root segments when hydrostatic pressure is applied.Abbreviations and symbols a _s outer surface of sleeve segment - c concentration of osmotically active solute - j _{v, s} radial volume flow density across sleeve segment - Lp_s hydraulic conductivity of sleeves - Lp_r hydraulic conductivity of intact roots - _N thickness of Nernst diffusion layer - reflection coefficient of root for solute - osmotic value of bulk phase - osmotic coefficient