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251.
252.
Uulke A. van der Heide Olaf E. Rem Hans C. Gerritsen Evert L. de Beer Piet Schiereck Ian P. Trayer Yehudi K. Levine 《European biophysics journal : EBJ》1994,23(5):369-378
A fluorescence depolarization study of the orientational distribution of crossbridges in dye-labelled muscle fibres is presented. The characterization of this distribution is important since the rotation of crossbridges is a key element in the theory of muscle contraction. In this study we exploited the advantages of angle-resolved experiments to characterize the principal features of the orientational distribution of the crossbridges in the muscle fibre. The directions of the transition dipole moments in the frame of the dye and the orientation and motion of the dye relative to the crossbridge determined previously were explicitly incorporated into the analysis of the experimental data. This afforded the unequivocal determination of all the second and fourth rank order parameters. Moreover, this additional information provided discrimination between different models for the orientational behaviour of the crossbridges. Our results indicate that no change of orientation takes place upon a transition from rigor to relaxation. The experiments, however, do no rule out a conformational change of the myosin S 1 during the transition.
Correspondence to: Y. K. Levine 相似文献
253.
254.
Cross talk between catabolic pathways in Pseudomonas putida: XylS-dependent and -independent activation of the TOL meta operon requires the same cis-acting sequences within the Pm promoter. 总被引:2,自引:1,他引:1 下载免费PDF全文
B Kessler S Marqus T Khler J L Ramos K N Timmis V de Lorenzo 《Journal of bacteriology》1994,176(17):5578-5582
255.
Heleen M. Van der Maas E. R. de Jong A. C. Van Aelst H. A. Verhoeven F. A. Krens J. L. Van Went 《Protoplasma》1994,178(1-2):48-56
Summary The cytoplasmic content and the distribution of intramembrane particles (IMPs) of the plasma membrane of isolated sperm cells of perennial ryegrass (Lolium perenne L.) have been characterized using flow cytometry, transmission electron microscopy, confocal scanning laser microscopy and freeze-fracture studies. The isolated haploid sperm cells contain a variety of cell organelles with the exception of microtubules. Proplastids and plastids with starch were observed, although only rarely. Vacuoles containing remnants of organelles and stacked lamellae of endoplasmic reticulum with cytoplasmic inclusions were observed frequently, indicating that autophagy takes place. The number of mitochondria varies from 11 to 26 with an average of 17. Generally, the nucleus has a lobed shape and displays various interphasic stages of chromatin condensation. The analysis of the number of mitochondria and the nuclear state did not show evidence of sperm cell dimorphism. The cytological variability observed, could be explained by differences in developmental stages already present in vivo at the moment of isolation. No correlation between the number of mitochondria and the nuclear cross-sectioned area and/or the condensation state of the chromatin could be found. The density of intramembrane particles of the plasma membrane on the exoplasmic fracture face is more than twice that on the protoplasmic fracture face. That is the opposite of what was found for sporophytic cells of perennial ryegrass. These results are discussed in relation to the potential use of these cells for biotechnology and developmental studies. 相似文献
256.
257.
Since the late eighties a handy and user-friendly sap flow meter (Dynagage®) is on the market which can quantify 0205 the sap flow through intact plant stems, based on the stem heat balance method. The documentation about its accuracy and reliability, however, is still too limited to use it as a standard method in field experiments with apple trees. We therefore tested this commercial system on potted apple trees (Malus domestica L.; cv. Red Elstar and Jonagold; on rootstock M9 vf) with stem diameters of 1.8 to 4 cm. The measured sap flow was compared with mass loss measured by an automated balance, supposing the total mass loss of the trees was equal to the water loss by transpiration. The results revealed three major problems:
In order to avoid these problems we constructed a sap flow meter which guarantees an optimum contact with the stem and works with continuously controlled power supply. Both aspects, response time and effect on the bark tissue, could be improved: in all measurement series the average sap flow (during light period) deviated <4% and=" often=">4%><1% from=" mass=" loss.=" the=" differences=" were=" usually=">1%><15% for=" the=" short-term=" averages=" through=" 15–30=" min.=" the=" modified=" sap=" flow=" meter=" also=" proved=" reliable=" during=" 10-day=" measurements=" in=" the=" field.=" however,=" for=" time-accurate=" measurements=" on=" apple=" trees=" with=" a=" stem=" diameter=">3–4 cm accounting for the energy stored in the heated stem section became indispensable.15%> 相似文献
1. | When there was no optimum contact of the elements of the gauge with the stem, which is typically very irregular on young apple trees, the calculated sap flow rates (accumulated through 24 h) showed errors >20%. |
2. | On 4 year-old trees the calculated sap flow rate showed considerable time lags in periods with abruptly changing transpiration rates, mainly because this sap flow method does not account for energy which is stored in the heated stem section. |
3. | The constant power input to the stem given with this sap flow meter caused heat damages to the bark tissue after >6 days of continuous measurements. |
258.
Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi 总被引:1,自引:0,他引:1
Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance. 相似文献
259.
Summary The lipophilicity (or hydrophobicity) of amino acids is an important property relevant for protein folding and therefore of great interest in protein engineering. For peptides or peptidomimetics of potential therapeutic interest, lipophilicity is related to absorption and distribution, and thus indirectly relates to their bioactivity. A rationalization of peptide lipophilicity requires basic knowledge of the lipophilicity of the constituting amino acids. In the present contribution we will review methods to measure or calculate the lipophilicities of amino acids, including unusual amino acids, and we will make a comparison between various lipophilicity scales. 相似文献
260.
Patrice Daniel Erwin de Waele Jean-Noël Hallet 《Applied microbiology and biotechnology》1993,38(5):638-641
Genomic DNA of several strains oof oenological lactic bacteria belonging to the species Lactobacillus plantarum, Leuconostoc oenos and Pediococcus pentosaceus was digested by the rare-cutting endonucleases ApaI and SmaI. The restriction products were separated by transverse alternating field electrophoresis (TAFE). The size of the genome of L. oenos estimated by adding the molecular size of the ApaI fragments was on average 1320 kb. A strong polymorphism was observed between the strains, which could be easily differentiated except for two industrial strains of L. oenos. A simple modification of the TAFE apparatus is proposed to improve the separation of the DNA fragments.
Correspondence to: J.-N. Hallet 相似文献