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81.
Seasonal variations in semen quality, freezability and plasma luteinizing hormone (LH) levels were studied between summer and spring. Semen volume, density and initial sperm motility did not differ significantly between different seasons. Plasma LH decreased between summer and spring but the differences were, however, not significant. Pre-freezing motility did not differ significantly but post-freezing motility varied significantly (P<0.01) between seasons. Post-freezing motility was lowest during summer and highest during winter. It can be concluded that summer spermatozoa may be fragile and cannot withstand freezing stress. To increase reproductive efficiency in buffalo during summer, semen should be frozen during winter and spring and used during hot weather conditions. Seasonal variations in plasma LH levels were insignificant. 相似文献
82.
Classical Conditioning-Induced Changes in Low-Molecular-Weight GTP-Binding Proteins in Rabbit Hippocampus 总被引:1,自引:0,他引:1
T. J. Nelson J.-V. Sanchez-Andres B. G. Schreurs D. L. Alkon 《Journal of neurochemistry》1991,57(6):2065-2069
Classical conditioning of Hermissenda, involving paired light-rotation events, results in a 30-35% decrease in the levels of a 20-kDa G protein (cp20). To test whether a similar protein exists in vertebrates, rabbits were trained to associate a tone with periorbital electrical stimulation and G proteins were analyzed by photoaffinity labeling with [alpha-32P]GTP-azidoanilide. A 20-kDa G protein similar to cp20 decreased by 36% in the hippocampus of rabbits subjected to paired tone and electrical stimulation, but not in unpaired controls. Learning-specific decreases were also found in the amount of ras protein. 相似文献
83.
It has been demonstrated that thermogenic activity of brown adipose tissue (BAT) is higher during the early postnatal period, decreasing towards a low adult level. The present study examined postnatal changes in the lipid composition of BAT. BAT from pre-weaning rats at 4 and 14 days old showed the following differences in lipid composition compared to that from adults of 12 weeks old. (i) Relative weight of interscapular BAT to body weight was markedly greater. (ii) BAT-triglyceride (TG) level was lower, while BAT-phospholipid (PL)level was higher. (iii) In TG fatty acids (FA) polyunsaturated fatty acids (PU; mol %), arachidonate index (AI), unsaturation index (UI) and PU/saturated FA (SA) were higher; rare FA such as eicosadienoate, bishomo--linolenic acid and lignoceric acid in mol % were also higher. (iv) In PL-FA monounsaturated FA (MU) in mol % was lower; PU mol %, AI and UI were higher. These features in BAT of pre-weaning rats resembled those in the cold-acclimated adults, suggesting a close relationship of the PL-FA profile to high activity of BAT. 相似文献
84.
Seasonal leaf water relations characteristics were studied in fully irrigated spring barley (Hordeum distichum L. cv. Gunnar) fertilized at low (50 kg K ha−1) or high (200 kg K ha−1) levels of potassium applied as KCl. The investigation was undertaken from about 14 days before anthesis until the milk ripe
stage in leaves of different position and age. Additionally, the effects of severe water stress on leaf water relations were
studied in the middle of the grain filling period in spring barley (cv. Alis). The leaf water relations characteristics were
determined by the pressure volume (PV) technique.
Water relations of fully irrigated plants were compared in leaf No 7 with the water relations of slowly droughted plants (cv.
Alis). Leaf osmotic potential at full turgor (ψ
π
100
) decreased 0.1 to 0.3 MPa in droughted leaves indicating a limited osmotic adjustment due to solute accumulation. The leaf
osmotic potential at zero turgor (ψ
π
0
) was about −2.2 MPa in fully irrigated plants and −2.6 MPa in droughted plants. The relative water content at zero turgor
(R0) decreased 0.1 unit in severely droughted leaves. The ratio of turgid leaf weight to dry weight (TW/DW) tended to be increased
by drought. The tissue modulus of elasticity (ε) decreased in droughted plants and together with osmotic adjustment mediated
turgor maintenance during drought. A similar response to drought was found in low and high K plants except that the R0 and ε values tended to be higher in the high K plants. Conclusively, during drought limited osmotic adjustment and increase
in elasticity of the leaf tissue mediated turgor maintenance. These effects were only slightly modified by high potassium
application.
The seasonal analysis in fully irrigated plants (cv. Gunnar) showed that within about 14 days from leaf emergence ψ
π
100
decreased from about −0.9 to −1.6 MPa in leaf No 7 (counting the first leaf to emerge as number one) and from about −1.1
to −1.9 MPa in leaf No 8 (the flag leaf) due to solute accumulation. A similar decrease took place in ψ
π
0
except that the level of ψ
π
0
was displaced to a lower level of about 0.2 to 0.3 MPa. Both ψ
π
100
and ψ
π
0
tended to be 0.05 to 0.10 MPa lower in high K than in low K plants. R0 was about 0.8 to 0.9 and was independent of leaf position and age, but tended to be highest in high K plants. The TW/DW ratio
decreased from about 5.5 in leaf No 6 to 4.5 in leaf No 7 and 3.8 in leaf No 8. The TW/DW ratio was 4 to 10% higher in high
K than in low K plants indicating larger leaf cell size in the former. The apoplastic water content (Va) at full turgor constituted about 15% in leaf No 7. ε was maximum at full turgor and varied from about 11 to 34 MPa. ε tended
to be higher in high K plants. Conclusively, in fully watered plants an ontogenetically determined accumulation of solutes
(probably organic as discussed) occurred in the leaves independent of K application. The main effect of high K application
on water relations was an increase in leaf water content and a slight decrease in leaf ψπ.
The effect of K status on growth and drought resistance is discussed. 相似文献
85.
Shih-fang Fan M. M. Dewey B. Gaylinn B. Chu 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(6):508-512
Summary In dynamic light scattering, measurements of the intensity-intensity time correlation function from a suspension of rod-like particles of length L could reveal dynamical information related to translational and internal motions of those particles. For a suspension of thick filaments isolated from the myosin-regulated, striated muscles of Limulus at KL>1 (where K is the scattering vector), the average characteristic linewidth (
) increased with the addition of Ca2+ or with the depletion of ATP. The increase in the
with the addition of Ca2+ could be due to the presence of energy-requiring, high-frequency motions of the crossbridges activated by Ca2+. The increase in
which occurred with the depletion of ATP was assumed to be mainly due to the thermal motions of the crossbridges after they had moved radially away from the filament backbone. The percentage increase in
following the addition of Ca2+ was found to be seasonal, i.e., values of
obtained from thick filaments isolated between the middle of June and the middle of September were smaller than those obtained during the rest of the year. The effect of temperature on the percentage increase in
was also different. The increase showed a maximum at about 35°C during the summer and at about 25°C at other times. However, the percentage increase in
developed under ATP-depleted conditions showed no temperature-related maximum. The number of bound Ca2+ per myosin molecule was 1 during the summer and 2 at other times.Abbreviations DLS
dynamic light scattering
- L
length
- K
scattering vector
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis
-
average characteristic line width
Deceased 相似文献
86.
A method has been devised to differentiate viable and nonviable bacterial spores. “Germination-like” changes are initiated in spores with performic acid and lysozyme. The germinated spores are stained with aqueous acridine orange, a fluorescent dye. Nonviable spores fluoresce lemon-green and viable spores orange-red. It is proposed that with the use of a membrane filter resistant to performic acid and lysozyme, the method may be used for spore enumeration in foods in about 4 hr compared to conventional plating methods, which usually require up to 72 hr. 相似文献
87.
Microstratification of phytoplankton in the large shallow Lake Balaton (Hungary) was studied during a 24 h period. Dissolved O2 showed biological stratification; flagellates exhibited a definite circadian rhythm. In the middle of the investigation a heavy storm broke out which was followed by the disappearance of differences between different layers of water. Storm-induced destratification is described by cluster-analysis. Abundances of dominant species changed differently in connection with the storm. Numbers of Nitzschia sp. increased due to stirring up from the sediment surface. Numbers of single-celled or colony-forming species (Cyclotella comta, Crucigenia quadrata, Coelosphaerium kuetzingianum) practically did not change. Numbers of all the three dominant filamentous species (Aphanizomenon fos-aquae f. klebahnii, Lyngbya limnetica, Planctonema lauterbornii) significantly decreased, which might be attributed to an unknown loss process and was followed by a competitive displacement by algae of small cell size. 相似文献
88.
A total of 300 samples was collected from February 1985 to August 1986 in a medium order Ozark Mountain stream. Physical habitat measurements of temperature, mean water column velocity, depth, and substrate character were recorded for each of the 25 monthly samples along with length and sex of all individuals of Orconectes neglectus (Faxon). Analysis of habitat utilization and suitability (or preference) was conducted using exponential polynomial models of hydraulic stress models. There appeared to be equal preference for depth over the range measured. Both substrate and velocity preference curves were bimodal with each mode designating certain crayfish size classes. Young-of-the-year were found primarily in cobbled, high velocity areas while adults were found in low velocity, macrophyte beds. Utilization curves for laminar sublayer thichness also reflected size-dependent phenomena where young-of-the-year were found in thin sublayer areas and adults were found primarily in thick sublayers. When separated by time and size, adults were found to occupy higher velocity, cobbled habitats during at least two months. This time period corresponded with the time of egg-bearing and further analysis yielded a time-dependent habitat suitability surface which accounted for this movement pattern. We suggest that the application of these suitability surfaces, which reflect habitat changes during the annual life cycle, will produce more accurate predictions of density and will allow better habitat management decisions under various regulated flow scenarios. 相似文献
89.
90.
Summary An ultrastructural and morphometric analysis was made of the nucleolar components in pinealocytes of 40 male Fischer rats sampled at eight times in an LD 1212 photoperiod cycle. Comparisons of results from the eight times showed variation in estimated mean volume of the granular component of ±29%, and of the fibrillar component ±11%, in relation to daily means. Peaks in mean volume of total nucleolus and its granular component occurred at 1 h of light. Near maximal and minimal mean volumes of the fibrillar component both occurred during both light and dark. Fibrillar centers (nucleolar organizer regions) of different sizes were found at all sampling times. It is concluded that temporal patterns in 24-h changes in the nucleolar components are most prominent in the granular component, and are more complex than suggested by changes in total nucleolar size or mean dimensions, and than represented by a simple biphasic circadian rhythm. Examples of different stages in the migration of the granular component, and of possible sites of nucleo-cytoplasmic transfer of nucleolar material, are described. 相似文献