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201.
Jo E. T. Strand Jan G. Davidsen Even H. J?rgensen Andun H. Rikardsen 《Environmental Biology of Fishes》2011,90(3):317-321
Two groups of migrating wild Atlantic salmon (Salmo salar) smolts caught within a 1 week interval in the River Alta, northern Norway, were tagged with acoustic transmitters and measured for gill Na+, K+ -ATPase activity in order to compare their smolt status with timing of sea entry. The first group of smolts had low levels of gill Na+, K+ -ATPase activity and resided in the lower part of the river twice as long as the second group that had high levels of gill Na+, K+ -ATPase activity. This indicates that early migrating smolts may not be completely physiologically adapted for salt water and delay their sea entry, thereby also synchronizing their seaward migration with the later migrating smolts. 相似文献
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Dystrophin-deficient skeletal muscles of mdx mice undergo their first rounds of degeneration-regeneration at the age of 14-28 days. This feature is thought to result from an increase in motor activity at weaning. In this study, we hypothesize that if the muscle is prevented from contracting, it will avoid the degenerative changes that normally occur. For this purpose, we developed a procedure of mechanical hindlimb immobilization in 3-wk-old mice to restrain soleus (Sol) and extensor digitorum longus (EDL) muscles in the stretched or shortened position. After a 14-day period of immobilization, the striking feature was the low percentage of regenerated (centronucleated) myofibers in Sol and EDL muscles, regardless of the length at which they were fixed, compared with those on the contralateral side (stretched Sol: 8.4 +/- 6.5 vs. 46.6 +/- 10.3%, P = 0.0008; shortened Sol: 1.2 +/- 1.6 vs. 50.4 +/- 16.4%, P = 0.0008; stretched EDL: 05 +/- 0.5 vs. 32.9 +/- 17.5%, P = 0. 002; shortened EDL: 3.3 +/- 3.1 vs. 34.7 +/- 11.1%, P = 0.002). Total numbers of myofibers did not change with immobilization. This study shows that limb immobilization prevents the occurrence of the first round of myofiber necrosis in mdx mice and suggests that muscle contractions play a role in the skeletal muscle degeneration of dystrophin-deficient mdx mouse muscles. 相似文献
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In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian
canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by
employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some
species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse
experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined
if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass
and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass
across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing
light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments
had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be
of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown
under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low
light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates
to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress
propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from
either type of propagule showed no differences in their morphological or physiological responses to varying light regimes.
Handling editor: S. M. Thomaz 相似文献
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