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排序方式: 共有52条查询结果,搜索用时 31 毫秒
1.
Oxalis regnellii Mig. is a trifoliate plant, and the three leaflets usually show synchronized up and down movements with a circadian period of 26–27 h. The three leaflets can also perform desynchronized ultradian oscillations, and we report on such rhythms under different conditions. A study of the occurrence of ultradian leaf movement rhythms as a function of irradiance is presented. At an irradiance of approximately 1 μW cm−2 , the occurrence was maximal and ca 30%. The periods varied from 5 to 15 h. Four other cases of ultradian rhythms in different conditions are also presented. In one case spontaneous ultradian rhythms occurred, and in another, two of the leaflets showed ultradian rhythms when the third leaflet had received a light pulse. In two more cases, the three leaflets on a leaf were separated by physical cuts along the petiole between the pulvini; in both cases the period was approximately 5 h. Possible mechanisms to explain the ultradian rhythms in Oxalis regnelli are discussed. 相似文献
2.
Runar Collander 《Protoplasma》1936,25(1):201-210
Ohne Zusammenfassung 相似文献
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Moccetti Paolo Siwertsson Anna Kjær Runar Amundsen Per-Arne Præbel Kim Tamayo Ana-Maria Peris Power Michael Knudsen Rune 《Hydrobiologia》2019,829(1):281-290
Hydrobiologia - Lipid biomarkers in sediments, which are indicative of biological production, provide important information regarding the environmental conditions in and around lakes, and can be... 相似文献
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Almaas R Pytte M Lindstad JK Wright M Saugstad OD Pleasure D Rootwelt T 《Journal of neurochemistry》2003,84(5):1018-1027
To study the effect of extracellular acidosis on apoptosis and necrosis during ischemia and reoxygenation, we exposed human post-mitotic NT2-N neurones to oxygen and glucose deprivation (OGD) followed by reoxygenation. In some experiments, pH of the cell medium was lowered to 5.9 during either OGD or reoxygenation or both. Staurosporine, used as a positive control for apoptosis, caused Poly(ADP-ribose)-polymerase (PARP) cleavage and nuclear fragmentation, but no PARP cleavage and little fragmentation were seen after OGD. Low molecular weight DNA fragments were found after staurosporine treatment, but not after OGD. No protective effect of caspase inhibitors was seen after 3 h of OGD and 21 h of reoxygenation, but after 45 h of reoxygenation caspase inhibition induced a modest improvement in 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) cleavage. While acidosis during OGD accompanied by neutral medium during reoxygenation protected the neurones (MTT: 228 +/- 117% of neutral medium, p < 0.001), acidosis during reoxygenation only was detrimental (MTT: 38 +/- 25%, p < 0.01). We conclude that apoptotic mechanisms play a minor role after OGD in NT2-N neurones. The effect of acidosis on neuronal survival depends on the timing of acidosis, as acidosis was protective during OGD and detrimental during reoxygenation. 相似文献
8.
Stokke R Madern D Fedøy AE Karlsen S Birkeland NK Steen IH 《Archives of microbiology》2007,187(5):361-370
The gene encoding isocitrate dehydrogenase (IDH) of Methylococcus capsulatus (McIDH) was cloned and overexpressed in Escherichia coli. The purified enzyme was NAD+-dependent with a thermal optimum for activity at 55–60°C and an apparent midpoint melting temperature (T
m) of 70°C. Analytical ultracentrifugation (AUC) revealed a homotetrameric state, and McIDH thus represents the first homotetrameric NAD+-dependent IDH that has been characterized. Based on a structural alignment of McIDH and homotetrameric homoisocitrate dehydrogenase (HDH) from Thermus thermophilus (TtHDH), we identified the clasp-like domain of McIDH as a likely site for tetramerization. McIDH showed moreover, higher sequence identity (48%) to TtHDH than to previously characterized IDHs. Putative NAD+-IDHs with high sequence identity (48–57%) to McIDH were however identified in a variety of bacteria showing that NAD+-dependent IDHs are indeed widespread within the domain, Bacteria. Phylogenetic analysis including these new sequences revealed
a close relationship with eukaryal allosterically regulated NAD+-IDH and the subfamily III of IDH was redefined to include bacterial NAD+- and NADP+-dependent IDHs. This apparent relationship suggests that the mitochondrial genes encoding NAD+-IDH are derived from the McIDH-like IDHs. 相似文献
9.
Melanoma cell lines are susceptible to histone deacetylase inhibitor TSA provoked cell cycle arrest and apoptosis 总被引:5,自引:0,他引:5
Peltonen K Kiviharju TM Järvinen PM Ra R Laiho M 《Pigment cell research / sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society》2005,18(3):196-202
Melanoma is the most aggressive of skin cancers because of its high resistance to currently available therapy. Although melanoma cells often retain wild-type p53 tumour suppressor protein and express it at high levels, the p53 mediated apoptosis pathway is suppressed. Histone deacetylase (HDAC) inhibitors are a promising group of compounds inducing differentiation, growth arrest and apoptosis in tumour cells in preclinical studies. We have studied the cellular effects of trichostatin A (TSA), a HDAC inhibitor, in a panel of melanoma cell lines and its mechanism of action in relation to p53. TSA stabilized wild-type p53, but p53 protein accumulation was overridden by simultaneous downregulation of p53 mRNA leading to a decrease in p53 protein. While growth arrest was induced in all cell lines studied and apoptosis in most (6/7), these cellular effects were independent of the p53 status of the cells. Inhibiting p53 function by a dominant negative p53 (p53(175His)) confirmed that the HDAC inhibitor induced apoptosis was independent of wild-type p53, even though TSA slightly activated p53 in a reporter assay. The results indicate that while the action of TSA is independent of p53, the activation of the apoptosis pathway by the HDAC inhibitors may provide therapeutic approaches for melanoma treatment. 相似文献
10.
Birte Töpper Aud Larsen Tron Frede Thingstad Runar Thyrhaug Ruth-Anne Sandaa 《Polar Biology》2010,33(11):1557-1565
In order to study interactions between microorganisms at different nutrient conditions in an arctic environment, a mesocosm
experiment was performed in Kongsfjorden, Svalbard (79°N). A phytoplankton bloom was initiated by daily additions of mineral
nutrients (ammonium and phosphate) to all mesocosm units. The addition of silicate and glucose, forming a factorial design
(+Si/+C, +Si/−C, −Si/+C, −Si/−C), was intended to produce different types of growth rate limitation for the bacterial community.
We here focus on the response in bacterial community composition to different nutrient situations. Phytoplankton, bacteria
and viruses were enumerated by flow cytometry, while denaturing gradient gel electrophoresis (DGGE) was used to track changes
in the bacterial community composition. Our results showed that both glucose and silicate addition affected the bacterial
community composition, with the largest effect from glucose. The initial increase in bacterial abundance was most pronounced
in the glucose units. After silicate addition, highest bacterial abundance was observed in the silicate treatments where mineral
nutrient competition by diatoms was expected to be highest. The major effect of glucose was expressed by the significant separation
of the +C and the −C samples at the end of the experiment, while silicate addition resulted in a more stable bacterial community
structure. In the unit, given both silicate and glucose, the diatoms were totally outcompeted by the bacterial community.
The competitive success of the heterotrophic bacteria in C-replete situations allows the conclusion that the bacteria were
not more negatively affected by low temperatures than phytoplankton. 相似文献