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21.
Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated
cholesterol in rats exposed daily to 357 and 714 μg Mn/kg for 30 d. Significant Mn accumulation was accompanied by increased
cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach
food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed
rats. The rats receiving 357 and 714 μg Mn/kg reached the food in 104.5±13.8 and 113.3±25.7 s, respectively, on d 30, whereas
their untreated counterparts reached the food in 28.7±11.4 s. This delay was completely corrected to 29.3±7.8 and 30.7±6.0
s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 μg/kg of Mn. The correction of
impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the
brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that
Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability. 相似文献
22.
Cold acclimation and photoinhibition of photosynthesis in Scots pine 总被引:13,自引:0,他引:13
Alla Krivosheeva Da-Li Tao Christina Ottander Gunnar Wingsle Sylvain L. Dube Gunnar Öquist 《Planta》1996,200(3):296-305
Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO2 uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.Abbreviations APX
ascorbate peroxidase
- DHA
dehydroascorbate
- DHAR
dehydroascorbate reductase
- Fm
maximal fluorescence when all reaction centres are closed
- Fv/Fm
maximum photochemical yield of PSII
- GR
glutathione reductase
- GSH
reduced glutathione
- Je
rate of photosynthetic electron transport
- MDAR
monodehydroascorbate reductase
- qN
nonphotochemical quenching of fluorescence
- qP
photochemical quenching of fluorescence
- SOD
superoxide dismutase
This work was supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China. 相似文献
23.
Örjan Totland 《American journal of botany》1996,83(4):452-458
Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self-incompatible Ranunculus acris L. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers of Ranunculus acris tracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production. 相似文献
24.
Flemming S. Vassbotn Arne
stman Nina Langeland Holm Holmsen Bengt Westermark Carl-Henrik Heldin Monica Nistr 《Journal of cellular physiology》1994,158(2):381-389
Human glioblastoma cells (A172) were found to concomitantly express PDGF-BB and PDGF β-receptors. The receptors were constitutively autophosphorylated in the absence of exogenous ligand, suggesting the presence of an autocrine PDGF pathway. Neutralizing PDGF antibodies as well as suramin inhibited the autonomous PDGF receptor tyrosine kinase activity and resulted in up-regulation of receptor protein. The interruption of the autocrine loop by the PDGF antibodies reversed the transformed phenotype of the glioblastoma cell, as determined by (1) diminished DNA synthesis, (2) inhibition of tumor colony growth, and (3) reversion of the transformed morphology of the tumor cells. The PDGF antibodies showed no effect on the DNA synthesis of another glioblastoma cells line (U343MGa 31L) or on Ki-ras-transformed fibroblasts. The present study demonstrates an endogenously activated PDGF pathway in a spontaneous human glioblastoma cell line. Furthermore, we provide evidence that the autocrine PDGF pathway drives the transtormed phenotype of the tumor cells, a process that can be blocked by extracellular antagonists. © 1994 Wiley-Liss, Inc. 相似文献
25.
A. J. Soitamo G. Zhou A. K. Clarke G. Öquist E-M. Aro P. Gustafsson 《Plant molecular biology》1994,26(2):709-721
The unicellular cyanobacterium Synechococcus sp. PCC 7942 has three psbA genes encoding two different forms of the photosystem II reaction centre protein D1 (D1:1 and D1:2). The level of expression of these psbA genes and the synthesis of D1:1 and D1:2 are strongly regulated under varying light conditions. In order to better understand the regulatory mechanisms underlying these processes, we have constructed a strain of Synechococcus sp. PCC 7942 capable of over-producing psbA mRNA and D1 protein. In this study, we describe the over-expression of D1:1 using a tac-hybrid promoter in front of the psbAI gene in combination with lacI
Q
repressor system. Over-production of D1:1 was induced by growing cells for 12 h at 50 mol photons m-2 s-1 in the presence of 40 or 80 g/ml IPTG. The amount of psbAI mRNA and that of D1:1 protein in cells grown with IPTG was three times and two times higher, respectively. A higher concentration of IPTG (i.e., 150 g/ml) did not further increase the production of the psbAI message or D1:1. The over-production of D1:1 caused a decrease in the level of D1:2 synthesised, resulting in most PSII reaction centres containing D1:1. However, the over-production of D1:1 had no effect on the pigment composition (chlorophyll a or phycocyanin/number of cells) or the light-saturated rate of photosynthesis. This and the fact that the total amounts of D1 and D2 proteins were not affected by IPTG suggest that the number of PSII centres within the membranes remained unchanged. From these results, we conclude that expression of psbAI can be regulated by using the tac promoter and lacI
Q
system. However, the accumulation of D1:1 protein into the membrane is regulated by the number of PSII centres. 相似文献
26.
Production and properties of inulinase from Aspergillus niger 总被引:5,自引:0,他引:5
Summary A thermostable inulinase was identified in a strain of A. niger. The highest activity was observed at 50 °C (50 Lml–1) and 77% and 34% of this was retained at 60° and 65°C, respectively. pH stability, the effect of thermal stabilizers such as Propylene glycol (10%) and Sorbitol (10%) and effects of different cations were investigated. It was found that the activity was completely inhibited by Ag+ and Hg2+, while Na+ had an activator effect. 相似文献
27.
Vladimir Divoky Erol Baysal Reyhan Öner M. Akif Çürük Emmitt L. D. Walker III Karel Indrak Titus H. J. Huisman 《Human genetics》1994,93(1):77-78
We have observed a TC mutation at position +96 of the untranslated region 3 to the terminating codon of the -globin gene in members of two Czech families and one black family. Data from initial studies suggested that this change was the cause of a -thalassemia, but continued analyses have provided convincing evidence that this mutation is a simple polymorphism. 相似文献
28.
The formation of gaseous compounds from decomposing fruibodies of three common macrofungi was qualitatively analysed. It was shown that significant production of ammonia took place. When the fruitbodies were decomposing on the surface of a podzolic forest floor more than 90% of the ammonia produced was absorbed by the soil, causing soil pH to increase. 相似文献
29.
Inger Kirstine Due Tuvesson Rebecka Charlotte Viktoria Öhlund 《Plant Cell, Tissue and Organ Culture》1993,34(2):163-167
Wheat microspores mechanically isolated from the anthers before culture and isolated from the anthers during the hole culture period in a chemically defined medium resulted in proembryos, embryos and finally plants. Of the four genotypes included, all responded with proembryos, and the two spring wheats Ciano and Walter gave rise to macroscopic embryos and plants. The frequency of embryo regeneration and the frequency of albino plants in both Ciano and Walter was in accordance with previously obtained results with anther culture derived material.Abbreviations 2,4-d
2,4-dichlorophenoxy acetic acid
- NAA
1-naphthaleneacetic acid 相似文献
30.