The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia. 相似文献
The addition of the proper amount of ammonium to the culture medium containing nitrate as nitrogen source enhanced the growth rate of Anabaena viguieri. The amount of geosmin produced by these cells varied with the concentrations of ammonium added. A negative correlation between the amount of geosmin produced and of the growth rate of cells was revealed. This was also found in cells grown on various forms of nitrogen sources. Without supply of any nitrogen compound, this organism is capable of fixing gaseous nitrogen, and under these conditions the cells grew relatively slowly. However, they produced more geosmin (per unit protein mass) than cells grown in the presence of combined nitrogen. The isolation of heterocysts, in which nitrogen was fixed, showed that these cells produced higher amounts of geosmin than vegetative cells. The possible relation of nitrogen assimilation to the production of geosmin in the cells was discussed. 相似文献
1. 1.|Changes in tissue metabolite concentrations and enzyme activities in the pedipalpal (PM) and heart (HM) muscles of the tropical scorpion Heterometrus fulvipes show that the metabolism in PM and HM is fundamentally reorganized following low (18°C) and high (38°C) temperature acclimation.
2. 2.|Changes in metabolite concentrations show that metabolite biosynthesis showed increases after cold acclimation but decreases after warm acclimation.
3. 3.|Similarly, changes in enzyme activities show a preponderance of glycolysis and HMP shunt activity after cold acclimation, while after warm acclimation glycogenolysis, oxidative metabolism and gluconeogenesis predominated.
4. 4.|Higher metabolite concentrations and enzyme activities both before and after thermal acclimation in HM reflect its greater compensatory abilities.
Abstract The process of colony formation by bacteria from grassland soil sampled in April, July and September was simulated by a colony-forming curve (CFC). The CFC was a super-imposition of several component curves (cCFC) given theoretically by the first order reaction (FOR) model [3,6]. The pattern of FOR model curves was not influenced by the time of sampling and four cCFCs were always recognized during an incubation period of 160 h. It was considered that the CFC describes an inherent property of the bacterial population of the field. Bacterial isolates were obtained from colonies produced in each of four cCFCs on agar plates. Isolates corresponding to one cCFC were classified as one group. The bacterial isolates were characterized by morphological and physiological tests and subsequently clustered. Few oligotrophic bacteria were obtained among bacteria which produced visible colonies within 63 h of incubation time. On the other hand, approx. 50% of bacteria which produced v colonies after 63 h were oligotrophic bacteria. The time required for the appearance of the first colony, t r of the FOR model, was very similar in the isolates belonging to one group. A close linear relationship was observed between t r value and doubling time of isolates. 相似文献
Abstract Predation rates of flagellate and ciliate protozoa on the bacterioplankton of Butrón River (Spain) were determined from FLB (fluorescently labelled bacteria) uptake rates. Bacterial and ciliate protozoa counts were higher when higher water temperature was recorded. Flagellate counts did not show this pattern, which suggested predation of flagellates by other organisms, or some other different nutritional mode besides phagotrophy. Average individual ciliate predation rates were up to 40-times higher than those of flagellates. These results were compared with similar data obtained from other authors in several aquatic systems. However, the population predation rates of flagellate protozoa were on average 6-times higher than that of ciliate protozoa, due to the low population numbers of the latter. Thus, flagellate protozoa can be considered as more important bacterial consumers than ciliates in this aquatic system. 相似文献
The apple maggot fly, Rhagoletis pomonella (Walsh), has only recently been found in Utah infesting sour cherry, Prunus cerasus L. An electrophoretic comparison of flies from Utah cherries with flies from Illinois hawthorns, Crataegus mollis (T. & G.) Scheele (a native host within the native range of the fly), show a marked reduction of genetic variability in the Utah sample. This result is indicative of a genetic bottleneck associated with the establishment of the apple maggot population in Utah cherries.
Résumé
R. pomonella (Walsh), est originaire de Crataegus dans l'Amérique du N.E. Il attaque de nombreux autres fruits, y compris les pommes et les cerises aigres (Prunus cerasus). La mouche a été récemment signalée en Utah, à la fois sur cerises et sur Crataegus douglasii. Nous avons comparé les niveaux de variabilité génétique d'une population de l'Utah contaminant les cerises et d'une population de l'Illinois contaminant C. mollis (la population de l'Illinois est représentative des niveaux de variabilité génétique dans l'aire d'origine de la mouche).La variabilité génétique à 17 loci a été évaluée par électrophorèse sur gel d'amidon. 10 de ces loci sont polymorphes dans la population d'Illinois, mais seulement 4 dans la population de l'Utah. Les fréquences alléliques de ces 4 loci de R. pomonella diffèrent significativement en Utah et en Illinois. La population de l'Utah présente nettement moins d'allèles par locus, un plus faible pourcentage de loci polymorphes et une hétérozygotie moyenne plus faible que la population de l'Illinois. Tous ces résultats sont conformes aux conséquences prévisibles d'un goulot d'étranglement.Deux explications existent pour cette perte de variabilité, toutes les deux liées à la combinaison de la faible taille de la population et de la dérive génétique ultérieure. Pour la première, la colonisation du cerisier par les mouches venant de Crataegus peut avoir provoqué un goulot d'étranglement génétique. Au contraire, la réduction de la variabilité peut avoir été la conséquence de la colonisation de l'Utah par R. pomonella. Nous retenons cette dernière comme la cause la plus vraisemblable de la variabilité génétique de la population de R. pomonella contaminant les cerises de l'Utah.
Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased. 相似文献
The photosynthetic and growth characteristics of Ceratophyllum demersum L. were investigated under laboratory conditions which simulated those encountered in the plants' normal environment. The carbon fixation rate of C. demersum measured with 14C at light and carbon saturation at pH 8.0 was 4.48 mg C (g ash-free dry weight)−1 h−1. It was lower at pH 6.5 than at pH 8.0. The light use efficiencies in quiescent plants and actively growing plants were 6.3 and 8.7 × 10−9 kg CO2 J−1, respectively, with corresponding maximum photosynthetic rates of 2.67 and 4.36 mg C (g ash-free dry weight)−1 h−1. Photorespiration in actively growing plants consumed 24% of the carbon fixed. Incubation with DCMU demonstrated that about one-third was refixed. The optimum temperature for carbon fixation was 25°C. The C3-photosynthetic pathway was the main operational route as indicated by the early photosynthetic products (largely C3-acids) and the absence of Krantz anatomy and the chlorophyll a:b ratio (2.7). The maximum relative growth rates ranged from 0.025 to 0.041 g ash-free dry weight (g ash-free dry weight)−1 day−1 in the field (Lake Vechten, 1 to 3 m depth classes). 相似文献