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1.
Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Qy region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.Abbreviations BChl
bacteriochlorophyll
- FWHM
full width at half maximum
- P-798
primary electron donor
- Tris
tris(hydroxymethyl)amino methane 相似文献
2.
3.
Richard E. Williamson 《Planta》1985,163(1):1-8
The mechanism by which sub-cortical actin bundles and membranous organelles are immobilised in the cortical cytoplasm of the alga Chara was studied by perfusing cells with a solution containing 1% Triton X-100. Light and scanning electron microscopy and the release of starch grains and chlorophyll-protein complexes indicated that the detergent extensively solubilised the chloroplasts. However, the sub-cortical actin bundles remained in situ even though they were originally separated from the plasma membrane by the chloroplasts. A fibrous layer between chloroplasts and plasma membrane became readily visible after detergent extraction of the cells and could be released by low-ionic-strength ethylenediaminetetraacetic acid, thioglycollate and trypsin. The same treatments applied to cells not subject to detergent extraction released the membrane-bound organelles and actin bundles and no fibrous meshwork was visible on subsequent extraction with Triton. It is, therefore, concluded that a detergent-insoluble cortical cytoskeleton exists and contributes to the immobility of the actin and cortical organelles in the cells.Abbreviation EDTA
ethylenediaminetetraacetic acid 相似文献
4.
David M. Glassman 《Primates; journal of primatology》1985,26(3):315-324
Intracortical bone remodeling and cortical thickness data were collected from middiaphyseal thin sections of the humerus,
ulna and tibia for 47 specimens ofSaguinus fuscicollis. Individuals were classified into age cohorts: Young Adult, Mid-adult I, Mid-adult II and Old Adult. Correlation analyses
revealed significant relationships between age cohort and the number of osteons for the humerus and ulna, and between age
cohort and non-Haversian canals for each of the three long bone elements. Significant relationships between age cohort and
dimension of cortex size suggested an age-related pattern of cortical shifting in the ulna and older-age bone loss in the
tibia. 相似文献
5.
James R. Hummert 《American journal of physical anthropology》1983,62(2):167-176
Cortical bone growth is analyzed for 174 children from a Medieval Christian population at Kulubnarti in the Batn el Hajar of Sudanese Nubia (550–1450 AD ). Using the tibia as a representative long bone, total subperiosteal area, cortical area, medullary area, and percent cortical area at midshaft were calculated. While growth in total and cortical areas, as well as in length, appear to be fairly well maintained, percent cortical area reveals unusual growth patterns which reflect excessive endosteal resorption. Compared to the relative reduction in bone mass which has been observed in malnourished living children, as well as with previously reported evidence for stress in the Kulubnarti population, the present data support an interpretation of nutritionally related stress and of no major diachronic dietary change. 相似文献
6.
Awake, unrestrained, and behaviourally normal animals with superfusion cannulae implanted over the sensorimotor cortex were used in a study of the capacity of infused [U-14C]glutamine for labelling glutamate and other amino acids released by depolarising stimuli. A spontaneous background release of [14C]glutamate was detected. This was increased by tityustoxin (1 microM). The specific radioactivity of glutamate increased eightfold during the evoked-release period. [14C]Aspartate was also detected and showed increased release, but not increased specific labelling, in response to depolarisation. Evoked gamma-aminobutyric acid (GABA) release occurred but only small amounts of [14C]GABA were detected. Glutamine showed increased rates of uptake to the sensorimotor cortex during stimulation periods, suggesting an accelerated breakdown via glutaminase. 相似文献
7.
8.
Anne Marpeau Jocelyne Walter Jacqueline Launay Jacqueline Charon Philippe Baradat Michel Gleizes 《Trees - Structure and Function》1989,3(4):220-226
Summary The effect of wounds on the volatile terpene composition of the living bark of Pinus pinaster Ait. (maritime pine) twigs was investigated with respect to the processes of mono- and sesquiterpene hydrocarbon biosynthesis. The large increase in the amounts of - and -pinene is a characteristic feature after a mechanical injury, whereas the quantities of the other terpenes are only slightly increased. This is due to the reactivation of the resin duct secretory cells of primary origin located in cortical tissues. The effect of wounding is observed over a long period and the terpene profiles are very different at the end of the experiments as compared with the initial profiles of the same tissues. The traumatic essential oil (obtained after mechanical traumatism) resembles an oleoresin extracted from tissues of secondary origin. Statistical analysis underlines the effects of the between-tree variations and of the dates of application of the wound. 相似文献
9.
Melissa A. Melan 《Protoplasma》1990,153(3):169-177
Summary We have investigated the effects of microtubule stabilizing conditions upon microtubule patterns in protoplasts and developed a new method for producing protoplasts which have non-random cortical microtubule arrays. Segments of elongating pea epicotyl tissue were treated with the microtubule stabilizing drug taxol for 1 h before enzymatic digestion of the cell walls in the presence of the drug. Anti-tubulin immunofluorescence showed that 40 M taxol preserved regions of ordered microtubules. The microtubules in these regions were arranged in parallel arrays, although the arrays did not always show the transverse orientation seen in the intact tissue. Protoplasts prepared without taxol had microtubules which were random in distribution. Addition of taxol to protoplasts with random microtubule arrangements did not result in organized microtubule arrays. Taxol-treated protoplasts were used to determine whether or not organized microtubule arrays would affect the organization of cell wall microfibrils as new walls were regenerated. We found that protoplasts from taxol-treated tissue which were allowed to regenerate cell walls produced organized arrays of microfibrils whose patterns matched those of the underlying microtubules. Protoplasts from untreated tissue synthesized microfibrils which were disordered. The synthesis of organized microfibrils by protoplasts with ordered microtubules arrays shows that microtubule arrangements in protoplasts influence the arrangement of newly synthesized microfibrils.Abbreviations DIC
differential interference contrast
- DMSO
dimethyl sulfoxide
- FITC
fluorescein isothiocyanate
- IgG
immunoglobulin G
- PIPES
piperazine-N,N-bis[2-ethane-sulfonic acid]
- PBS
phosphate buffered saline 相似文献
10.
Depolarisation of [3H]inositol-prelabelled slices of rat cerebral cortex with elevated extracellular K+ induced a rapid and marked increase in inositol polyphosphate accumulation. Addition of the muscarinic antagonist atropine (10 microM) markedly inhibited the K+-induced accumulation of inositol tetrakisphosphate (InsP4), with only a slight reduction in stimulated inositol bis- and trisphosphate levels. Inhibitory effects on InsP4 were noted at the earliest time period measured (30 s) and suggested the involvement of released endogenous acetylcholine in part of the response. The atropine-insensitive component of depolarisation did not appear to be secondary to release of noradrenaline, histamine, or 5-hydroxytryptamine, because addition of prazosin, mepyramine, or ketanserin was without effect on the K+ response. Furthermore, secretion of a neuropeptide that could stimulate phosphoinositide hydrolysis was unlikely, because the peptidase inhibitor bacitracin was also without effect. The results suggest that endogenous acetylcholine can stimulate phosphoinositide metabolism by interacting with muscarinic receptors and that this is particularly evident on InsP4 accumulation. Atropine-insensitive responses may be secondary to Ca2+ entry via voltage-sensitive channels. 相似文献