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81.
Niels Kroer 《FEMS microbiology ecology》1994,13(3):217-224
Abstract Cell volume, carbon and nitrogen content were determined for bacteria grown in batch cultures in water samples collected at five localities in western Florida, USA. Cultures were set up by inoculating 0.2 μm filtered water with 2.5 to 7.0% of 1.0 μm filtered water. Biovolumes of the bacteria were measured by epifluorescence photomicrography. Bacterial carbon and nitrogen contents were determined with a CHN analyser. During incubations, bacterial volumes doubled from 0.070±0.037 μ m3 (mean ± S.E.) to 0.153 ± 0.036 μ m3 at early stationary phase. Bacterial C:N ratios ranged between 2.8 and 10.3, with a mean of 6.5, and were inversely correlated with cell volumes. Conversion factors for volume to carbon and nitrogen content were relatively high and variable, ranging from 0.21 to 161 pg C μm−3 (mean: 0.72 pg C μm−3 ) and from 0.05 to 0.25 pg N μm−3 (mean: 0.12 pg N μm−3 ). Small cells contained more C and N per unit volume than did large cells. The data suggested that biovolume to biomass conversion factors may be higher than previously thought and may be highly variable both temporally and geographically. 相似文献
82.
To study the influence of soil moisture on phosphorus (P) depletion in the rhizosphere, maize (Zea mays cv. Trak) was pre-grown in vermiculite filled-PVC tubes for 9 days and then the plants with the tubes were transplanted into soil columns maintained at two soil moisture levels () of 0.14 and 0.20 cm3 cm–3 for 10 days. The soil columns were separated at 1 cm depth by a nylon screen of 53 m inner mesh size, into 1 cm soil layer above and 3 cm soil column below screen. A root mat developed over the screen, but root hairs only could penetrate it. Regardless of the soil moisture level in the columns, and adequate and equal water and nutrients supply was maintained via wicks from an external nutrient solution to the plant roots in vermiculite. After 10 days, the soil columns were separated from the root mats, quickly frozen in liquid nitrogen and sliced into thin layers (0.2mm) using a refrigerated microtome to give soil samples at defined distances from the root mats for analyses. Lower soil moisture (=0.14) resulted in narrower and steeper depletion profile of 0.5 M NaHCO3 extractable P (NaHCO3-Pi) as compared to higher soil moisture (=0.20). Depletion of P in soil solution in the immediate vicinity of root mats did not differ much but the extension of the depletion zones was 0.10 cm at =0.14 and 0.20 cm at =0.20. The depletion up to 0.05cm with =0.14 and up to 0.07 cm with =0.20 was uniform, and may be attributed to the depletion in the root hair zone. Beyond the root hair zones, the theory of diffusion and mass flow was able to explain the observed differences in shape and extent of the P depletion profiles at the two soil moisture levels. 相似文献
83.
Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and kLa was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum kLa that can be measured by this method in a standard laboratory scale bioreactor is 145 h–1 corresponding to a temperature change rate of 320°C h–1.Nomenclature p
Difference between pG and pL (% saturation)
- T
Ramp change of temperature (°C)
- E
Temperature-compensated output from the oxygen electrode (A)
- Eu
Uncompensated output from the oxygen electrode (A)
- kLa
Overall volumetric mass transfer coefficient (h–1)
- kLaTm
Overall volumetric mass transfer coefficient at temperature Tm (h–1)
- PG
Dissolved oxygen activity in equilibrium with the gas phase (% saturation)
- pL
Dissolved oxygen activity (% saturation)
- pLm
Dissolved oxygen activity at time tm (% saturation)
- t
Time (h)
- tm
Time of maximum p (h)
- T
Temperature (°C)
- Tcal
Calibration temperature of the oxygen electrode (°C)
- Tm
Final temperature after a temperature shift (°C)
- Tn
Temperature at time tn 相似文献
84.
85.
E B Olsen S R Lowenstein J Koziol-McLain J G Summers 《The Western journal of medicine》1993,158(5):484
We observed 55 inpatients with "do-not-resuscitate" (DNR) orders to determine what happened to their DNR status after hospital discharge. All were admitted to the medical service of a Department of Veterans Affairs hospital. Of the 55 patients, 16 died in the hospital, 10 were discharged to inpatient hospice units, and 1 was transferred to an acute care hospital. An additional 19 patients were discharged to nursing homes. The other 9 patients (16% of the total) survived their hospital stays; 6 successful contacts were made with patients'' spouses. In 1 case the spouse thought a DNR order was no longer desirable. In the other 5 cases the spouse said the DNR status was "probably" or "definitely" still warranted, but only 1 spouse had a written DNR order at home. We contacted 9 of the 14 house officers who had cared for the patients in hospital. Only 2 had ever written a DNR order after hospital discharge. Two house officers said they routinely discussed with family members a patient''s expected dying process at home. Unwanted resuscitation is as undesirable at home as in the hospital. Physicians should discuss future resuscitation procedures with patients who have DNR orders at the time of hospital discharge. Physicians, paramedic service directors, and policymakers also should develop protocols and standardized home DNR orders so that paramedics can honor the wishes of patients in the prehospital setting. 相似文献
86.
The variation pattern in the perennial Hordeum brachyantherum complex and in the annual H. depressum are described. The diploid form of H. brachyantherum s. lat., endemic to California in USA, previously recognized as a separate species is here treated as a subspecies ( H. brachyantherum ssp. californicum ). Despite its restricted distribution it shows a considerable variation and overlap in morphology with the tetraploid ssp. brachyantherum , and no unambiguous determination based on morphology between the two tax a is possible. The tetraploid cytotype has a large distribution area in western North America and easternmost Asia and a very wide morphological variation. It has also a small disjunct distribution area in easternmost Canada. A single hexaploid population from California is referred to ssp. brachyantherum . 相似文献
87.
88.
Fibril assembly and carotenoid overaccumulation in chromoplasts: a model for supramolecular lipoprotein structures. 总被引:16,自引:4,他引:12 下载免费PDF全文
Chromoplast development in ripening bell pepper fruits is characterized by a massive synthesis of carotenoid pigments, resulting in their distinctive red color. We have shown that 95% of these pigments accumulate in chromoplasts in specific lipoprotein fibrils. In addition to carotenoids, purified fibrils contain galactolipids, phospholipids, and a single, 32-kD protein, designated fibrillin, which has antigenically related counterparts in other species. Fibrils were reconstituted in vitro when purified fibrillin was combined with carotenoids and polar lipids in the same stoichiometric ratio found in fibrils in vivo. Antibodies directed against fibrillin were used to isolate a fibrillin cDNA clone and, in immunological studies, to follow its accumulation during the chloroplast-to-chromoplast transition under different conditions. A model for fibril architecture is proposed wherein carotenoids accumulate in the center of the fibrils and are surrounded by a layer of polar lipids, which in turn are surrounded by an outer layer of fibrillin. Topological analysis of purified fibrils verified this structure. Collectively, these results suggest that the process of fibril self-assembly in chromoplasts is an example of a general phenomenon shared among cells that target excess membrane lipids into deposit structures to avoid their destabilizing or toxic effects. In addition, we have shown that abscisic acid stimulates this phenomenon in chromoplasts, whereas gibberellic acid and auxin delay it. 相似文献
89.
Regeneration of Fertile Barley Plants from Mechanically Isolated Protoplasts of the Fertilized Egg Cell 总被引:20,自引:0,他引:20 下载免费PDF全文
A simple procedure is described for the mechanical isolation of protoplasts of unfertilized and fertilized barley egg cells from dissected ovules. Viable protoplasts were isolated from ~75% of the dissected ovules. Unfertilized protoplasts did not divide, whereas almost all fertilized protoplasts developed into microcalli. These degenerated when grown in medium only. When cocultivated with barley microspores undergoing microspore embryogenesis, the protoplasts of the fertilized egg cells developed into embryo-like structures that gave rise to fully fertile plants. On average, 75% of cocultivated protoplasts of fertilized egg cells developed into embryo-like structures. Fully fertile plants were regenerated from ~50% of the embryo-like structures. The isolation-regeneration techniques may be largely genotype independent, because similar frequencies were obtained in two different barley varieties with very different performance in anther and microspore culture. Protoplasts of unfertilized and fertilized eggs of wheat were isolated by the same procedure, and a fully fertile wheat plant was regenerated by cocultivation with barley microspores. 相似文献
90.
Slow cortical potential biofeedback and the startle reflex 总被引:4,自引:0,他引:4
Stuart Brody Harald Rau Fabiola Köhler Harald Schupp Werner Lutzenberger Niels Birbaumer 《Applied psychophysiology and biofeedback》1994,19(1):1-11
The negativity of slow cortical potentials (SCP) of the surface EEG is a measure of brain excitability, correlating with motor and cognitive preparation. Selfcontrol of SCP positivity has been shown to reduce seizure activity. Following SCP biofeedback from a central EEG electrode position, subjects gained bidirectional control over their SCP. The current study used a modified feedback methodology, and found a positive relationship between negativity and magnitude of EMG startle response (a measure of cortical and subcortical arousal, particularly aversive response disposition). Greater success in SCP differentiation was associated with self-report of less relaxation during negativity training.This research was supported by the Deutsche Forschungsgemeinschaft under grant No. SFB 307. 相似文献