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61.
Proximal tubule cells of the mouse kidney (metanephros) are normally extremely responsive to testosterone and its intracellular metabolites. The X-linked Tfm mutation recovered by Lyon and Hawkes seems to represent an is (repressor noninducible) mutation of the regulatory locus. 相似文献
62.
HAAG-KERWER ANGELA; FRANCO AUGUSTO C.; LUTTGE ULRICH 《Journal of experimental botany》1992,43(3):345-352
Gas exchange and organic acid accumulation of the C3-CAM intermediateClusia minor L. were investigated in response to various day/nighttemperatures and two light regimes (low and high PAR). For bothlight levels equal day/night temperatures between 20°C and30°C caused a typical C3 gas exchange pattern with all CO2uptake occurring during daylight hours. A day/ night temperatureof 15°C caused a negative CO2 balance over a 24 h periodfor low-PAR-grown plants while high-PAR-grown plants showeda CAM gas exchange pattern with most CO2 uptake taking placeduring the dark period. However, there was always a considerablenight-time accumulation of malic acid which increased when thenight-time temperature was lowered and had its maximum (54 mmolm2) at day/night temperature of 30/15°C. A significantamount of malic acid accumulation (23 mmol m2) in low-PAR-grownplants was observed only at 30/15°C. Recycling of respiratoryCO2 in terms of malic acid accumulation reached between 2·0and 21·5 mmol m2 for high-PAR-grown plants whilethere was no significant recycling for low-PAR-grown plants.Both low and high-PAR-grown plants showed considerable night-timeaccumulation of citric acid. Indeed under several temperatureregimes low-PAR-grown plants showed day/night changes in citricacid levels whereas malic acid levels remained approximatelyconstant or slightly decreased. It is hypothesized that lowand high-PAR-grown plants have different requirements for citrate.In high-PAR-grown plants, the breakdown of citrate preventsphotoinhibition by increasing internal CO2 levels, whereas inlow-PAR-grown plants the night-time accumulation of citric acidmay function as an energy and carbon saving mechanism. Key words: C. minor, C3, CAM, citric acid, light intensity 相似文献
63.
Tissue localization of u.v.-B-screening pigments and of chalcone synthase mRNA in needles of Scots pine seedlings 总被引:1,自引:0,他引:1
64.
A study was made of the distribution of Co60 in various tissues and organs of normal and alloxan diabetic rats during the first 24 hr. following injection. No significant statistical differences were observed between the two groups of animals. Radioautographs of the pancreas in the two groups failed to provide any evidence that the cobalt in this organ might be concentrated in the islets of Langerhans. 相似文献
65.
66.
We studied the physiological response of Pseudocalanus sp. under four different temperature elevation regimes: +0, +2, +4 and +6 °C above the decadal average temperature in the Western Baltic Sea. We measured fecal pellet (FP) production rates, which was taken as a proxy of ingestion, egg production (EPR) and respiration rates. Experiments lasted from mid‐February to end April, corresponding most of the observations to the postspring bloom phase. We combined small scale incubations with the use of big (ca. 1400 L) mesocosms, which have previously been shown to be appropriate when studying phyto‐ and zooplankton succession, and the water used for the incubations was taken from the mesocosm tanks. Given that the phytoplankton succession varied between the four thermal scenarios, we evaluated (excepting in the case of the respiration rates, where incubations were carried out using 0.2 μm filtered water) both the temperature and the associated food concentration effects. Respiration and ingestion rates were found to increase with temperature. As for EPR, they also increased with temperature during the bloom, but remained at low and constant values during the postbloom in all the four treatments due to the food limitation. Linked to the temperature rise, we also detected an increase in instantaneous mortality rates and a reduction in the net growth efficiency. Finally, we discuss the potential implications of our findings for the spring phyto‐ and zooplankton succession under the forecasted climate warming, as well as for the fisheries in the Baltic Sea, where Pseudocalanus sp. is a key species. 相似文献
67.
Climate change and the timing, magnitude, and composition of the phytoplankton spring bloom 总被引:2,自引:0,他引:2
In this article, we show by mesocosm experiments that winter and spring warming will lead to substantial changes in the spring bloom of phytoplankton. The timing of the spring bloom shows only little response to warming as such, while light appears to play a more important role in its initiation. The daily light dose needed for the start of the phytoplankton spring bloom in our experiments agrees well with a recently published critical light intensity found in a field survey of the North Atlantic (around 1.3 mol photons m?2 day?1). Experimental temperature elevation had a strong effect on phytoplankton peak biomass (decreasing with temperature), mean cell size (decreasing with temperature) and on the share of microplankton diatoms (decreasing with temperature). All these changes will lead to poorer feeding conditions for copepod zooplankton and, thus, to a less efficient energy transfer from primary to fish production under a warmer climate. 相似文献
68.
69.
Caterpillars and spider mites are herbivores with different feeding mechanisms. Spider mites feed on the cell content via stylets, while caterpillars, as chewing herbivores, remove larger amounts of photosynthetically active tissue. We investigated local and systemic effects of short-term caterpillar and spider mite herbivory on cotton in terms of primary metabolism and growth processes. After short-term caterpillar feeding, leaf growth and water content were decreased in damaged leaves. The glutamate/glutamine ratio increased and other free amino acids were also affected. In contrast, mild spider mite infestation did not affect leaf growth or amino acid composition, but led to an increase in total nitrogen and sucrose concentrations. Both herbivores induced locally increased dark respiration, suggesting an increased mobilization of storage compounds potentially available for synthesis of defensive substances, but did not affect assimilation and transpiration. Systemically induced leaves were not significantly affected by the treatments performed in this study. The results show that cotton plants do not compensate the loss of photosynthetic tissue with higher photosynthetic efficiency of the remaining tissue. However, early plant responses to different herbivores leave their signature in primary metabolism, affecting leaf growth. Changes in amino acid concentrations, total nitrogen and sucrose content may affect subsequent herbivore performance. 相似文献
70.
BJÖRN C. RALL OLIVERA VUCIC‐PESTIC ROSWITHA B. EHNES MARK EMMERSON ULRICH BROSE 《Global Change Biology》2010,16(8):2145-2157
Warming could strongly stabilize or destabilize populations and food webs by changing the interaction strengths between predators and their prey. Predicting the consequences of warming requires understanding how temperature affects ingestion (energy gain) and metabolism (energy loss). Here, we studied the temperature dependence of metabolism and ingestion in laboratory experiments with terrestrial arthropods (beetles and spiders). From this data, we calculated ingestion efficiencies (ingestion/metabolism) and per capita interaction strengths in the short and long term. Additionally, we investigated if and how body mass changes these temperature dependencies. For both predator groups, warming increased metabolic rates substantially, whereas temperature effects on ingestion rates were weak. Accordingly, the ingestion efficiency (the ratio of ingestion to metabolism) decreased in all treatments. This result has two possible consequences: on the one hand, it suggests that warming of natural ecosystems could increase intrinsic population stability, meaning less fluctuations in population density; on the other hand, decreasing ingestion efficiencies may also lead to higher extinction risks because of starvation. Additionally, predicted long‐term per capita interaction strengths decreased with warming, which suggests an increase in perturbation stability of populations, i.e., a higher probability of returning to the same equilibrium density after a small perturbation. Together, these results suggest that warming has complex and potentially profound effects on predator–prey interactions and food‐web stability. 相似文献