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831.
In order to establish in a new geographical area, introduced insects must be able to survive any period of adverse conditions such as a temperate winter and be capable of subsequent development to adulthood and/or reproduction. However, this aspect of insect overwintering and cold tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshouses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of time during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult female Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non-stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though cold treated larvae took approximately two days longer to reach adulthood than untreated individuals (at 20°C, 18L:6D). Chill treatment of adult females significantly reduced their rate of reproduction (from 1.45 to 0.93 larvae day-1), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10.8 larvae), compared to control females. Acute exposure resulted in non-significant decreases of the same parameters. The relevance of the above effects to overwintering of F. occidentalis is discussed. 相似文献
832.
In this experimental study, the effect of cadmium on cold and restraint stress-induced gastric lesions has been studied. Rats
received 15 μg/mL cadmium-containing water for 30 d, and at the end of this period, they were subjected to cold and restraint
stress.
Cadmium accumulation in gastric mucosa was associated with increased mucosal lesions, as well as decreased mucin and PGE2 levels in rats exposed to cadmium. Stress-induced mucosal injury was more pronounced, and the hemoglobin leakage into gastric
lumen owing to breakdown in the barrier was 17.30±3.45 μg/mL in control and 35.71±6.18 μg/mL in treated rats. Our data suggest
that high cadmium intake facilitates the occurence of stress-induced mucosal lesions by diminishing the mucin content and
PGE2 generation in gastric mucosa. 相似文献
833.
Magnetic resonance imaging (MRI) of water during cold acclimation and freezing in winter wheat 总被引:4,自引:2,他引:2
Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) were used to analyse changes in the physical state of water in wheat crowns during cold acclimation and during the freezing/thawing cycle. Spectroscopically measured average spin-spin relaxation times (T2) decreased during cold acclimation and increased when plants were grown at normal temperature. Spin-spin relaxation images whose contrast is proportional to T2, times were calculated allowing association of water relaxation with regions of tissue in spin-echo images during acclimation and freezing. Images taken during freezing revealed nonuniform freezing of tissue in crowns and roots. Acclimated and non-acclimated wheat crowns were imaged during freezing and after thawing. Spin-echo image signal intensity and T2 times decreased dramatically between -4°C and -8°C as a result of a decrease in water mobility during freezing. Images collected during thawing were diffuse with less structure and relaxation times were longer, consistent with water redistribution in tissue after membrane damage. 相似文献
834.
835.
Order parameters of chloroplast membrane lipids of rye wheat seedlings differing in cold hardiness were compared before after hardening. Seedlings grown at 25° exhibited similar membrane microviscosities. When hardened, the cultivars most resistant to freezing temperatures possessed the most fluid membranes, while those sensitive to cold were unable to alter them. Changes in linolenic acid levels alone cannot be responsible for the observed phenomena. 相似文献
836.
1. Temperature- and time-dependent mortalities were studied and modelled in insects exposed in regimes with constant and alternating temperatures. In these experiments, freezing was not a cause of death.
2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta .
3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h).
4. The injury was reversible when the cold exposure was limited to 2 days.
5. Survival in desiccated animals (14% water loss) was reduced.
6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures. 相似文献
2. Survival rates at a range of constant low temperatures (– 5 to + 1 °C) and for different exposure periods (1–14 days) were measured in the summer acclimated springtail Orchesella cincta .
3. Daily interruptions of the cold exposure with short intervals at high temperature reduced mortality or slowed the increase of mortality. This effect was stronger at higher temperature (19 vs 5 and 12 °C) and increased with the duration of the interruption (0·25–2 h).
4. The injury was reversible when the cold exposure was limited to 2 days.
5. Survival in desiccated animals (14% water loss) was reduced.
6. It is suggested that the mortality of summer acclimated springtails is caused by a complex metabolic disorder and membrane changes at low temperatures. 相似文献
837.
838.
The present paper reports structure prediction and analysis of a psychrophilic β-mannanase from Glaciozyma antarctica PI12 yeast. A threading method was used for 3D structure prediction of the enzyme using the MODELLER 9v12 program regarding its low sequence identity (<30%). The constructed model has been used in a comparative study to analyse its cold adaptation mechanism using other mesophilic, thermophilic, and hyperthermophilic mannanases. The structural and molecular dynamics analysis suggests that flexibility of the enzyme is increased through different structural characteristics, and therefore, the possibility of efficient catalytic reactions is provided at cold environment. These characteristics are the presence of longer loops, broken or shorter strands and helices, a lower number of salt bridges and hydrogen bonds, a higher exposure of the hydrophobic side chains to the solvent and an increased total solvent accessible surface area. Furthermore, the high catalytic efficiency and structural flexibility of the psychrophilic mannanase was supported by the results of principal component analysis. 相似文献
839.
THE ECOLOGICAL SIGNIFICANCE OF FRUCTAN IN A CONTEMPORARY FLORA 总被引:23,自引:17,他引:6
GEORGE HENDRY 《The New phytologist》1987,106(S1):201-216
840.
R. A. Skeffington 《Plant and Soil》1990,128(1):1-11
This paper considers whether new problems are arising in forest ecosystems due to increased levels of inorganic N deposition from the atmosphere, or whether there are no new problems, just a change of perception. Deposition of N has indeed increased. Wet deposition rates are reasonably quantified, but the rates of dry deposition to forests are largely unknown. Current transport and deposition models are probably under-estimating N deposition to forests. Consideration of possible effects of enhanced N deposition reveals with varying degrees of certainty that there may be effects due to high N in biomass, high uptake rates, leaching of nitrate and consequent acidification, and an overall increase in N availability. Forest ecosystems are not well-enough understood to set a critical load for N deposition, but enough is known to define some upper limits. 相似文献