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261.
262.
Ingunn Ims Vistnes Christian Nellemann Per Jordhøy Ole-Gunnar Støen 《Polar Biology》2008,31(11):1307-1317
We examined the summer distribution of 2,500 wild reindeer (Rangifer tarandus tarandus) in southern Norway by eight aerial surveys across 8 years. Most of the reindeer were located at high elevations >1,400 m.a.s.l.
(88% of the reindeer in 47% of the area) where insect stress was lower. Within high elevations, reindeer used areas <5.0 km
from tourist resorts and major roads and <2.5 km from hiking trails less than expected from availability. A total of 65% of
the reindeer were found in high-altitude areas without human development or only including closed maintenance roads, which
constituted 21% of the area, likely because these areas gave shelter from both insect stress and human activity. We conclude
that wild reindeer appear to select for insect relief areas reaching several kilometers away from human activity if such habitat
is available. Infrastructure with associated human activity was found to be avoided in all surveys. 相似文献
263.
Movement ofMimosa pudica L. pulvinules was investigated by using excised ones which were placed on a moist filter paper. The pulvinules excised in
the morning opened at the addition of IAA (10−7 M to 10−4M) in the dark. The lag period for the onset of the opening was about 15 min. Na-acetate buffer (pH 4) also induced the opening
of pulvinules in the dark, and the buffer-induced opening was inhibited by the uncouplers of oxidative phosphorylation. Na-MES
and Na-citrate buffers (pH 4) did not induce the opening.
Pulvinules taken from closed leaves in the evening were less responsive to IAA than those taken from open leaves in the morning.
The pulvinules taken in the evening slightly opened with incandescent light (4000 lux), but those preincubated with IAA (10−7M and 10−6M) opened distinctly upon the illumination. 相似文献
264.
We use the modified self-consistent phonon approximation theory to calculate temperature dependent interbase hydrogen bond
disruption profiles for a number of six base pair repeating sequence infinite B-DNA polymers with various guanine-cytosine/adenine-thymine
ratios. For comparison we also include results we have obtained in our earlier work on several B-DNA homopolymers, copolymers
and a four-base-pair repeating sequence polymer. Our theory gives a statistical estimate of thermal fluctuational disruption
probability of individual hydrogen bonds in individual base pairs in DNA as a function of temperature. The calculated probabilities
show no sequence dependence at premelting temperatures, in agreement with proton exchange measurements. These probabilities
however become very sensitive to base sequence at temperatures close to the observed melting temperatures. Multi-phasic critical
transitions are found in which a portion of base pairs are disrupted at temperatures below the final disruption temperature.
These transitions include localized as well as non-localized base pair opening. The localized transitions involve disruption
of a few base-pairs at every other location without large scale base unstacking, and they may not appear in the observed UV
curves with current resolution. On the other hand the overall disruption behavior is consistent with observations. The midpoint
transition temperatures are close to the observed melting temperatures and these temperatures show the observed linear dependence
on guanine-cytosine content. Our calculations indicate that our theory can be used effectively to calculate H-bond disruption
behavior of different DNA sequences.
Received: 20 February 1996 / Accepted: 2 May 1996 相似文献
265.
Reactions of ethyleneimine with guanosine and deoxyguanosine 总被引:2,自引:0,他引:2
K Hemminki 《Chemico-biological interactions》1984,48(3):249-260
Ethyleneimine was reacted with guanosine in aqueous medium and the products were purified by Sephadex G-10 and high-performance liquid chromatography (HPLC). Two products were identified by UV-spectroscopy: imidazole-ring opened 7-alkylguanosine and 1-alkylguanosine, accounting for 80% and 14% of all adduct radioactivity, respectively. When the incubation with ethyleneimine and guanosine or deoxyguanosine was carried out at pH 6.0 for 1 h intact 7-alkylation products were detected. The half-life of imidazole ring opening of 7-alkylguanosine was 11, 5 and 2.8 min at pH-values 7.0, 7.7 and 8.0, respectively, as measured fluorometrically at 25 degrees C. The respective half-life of alkylated deoxyguanosine was 21 min at pH 7.7. The half-life of depurination of alkylated deoxyguanosine was 42 min at pH 6.0 and 25 degrees C. 相似文献