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排序方式: 共有46条查询结果,搜索用时 15 毫秒
1.
When dried organisms are immersed in water, rapid imbibition may cause severe damage to plasma membranes; in unicellular organisms, such damage is usually lethal. This study investigated effects of water activity (dryness) of organisms and immersion temperature on imbibitional damage in three insect pathogenic fungi. Conidial powders of Beauveria bassiana (Bb), Metarhizium anisopliae (Ma) and Metarhizium acridum (Mac) were dried/hydrated to a broad range of water activities (aw) (0.023–0.961) prior to immersion in water at 0.5–33 °C. Imbibitional damage in conidia of each fungus occurred rapidly, with no differences in viabilities observed following immersion for 2 vs. 60 min. Damage increased with decreasing water activity of the conidia and decreasing temperature of the immersion water. Dry (aw  0.333) Metarhizium spp. conidia were highly susceptible to imbibitional damage, with viability declining to 5% after immersion at 0.5 °C and 63% following immersion at 15 °C. Germination of the driest Ma conidia was reduced to 66% after treatment at 25 °C. In contrast, Bb was highly tolerant to damage, with significant reductions in viability (to levels as low as 43–65%) occurring only when dry conidia were immersed at 0.5 °C. Damage was prevented when conidia were slowly rehydrated by humidification prior to immersion and immersion temperature was increased to 33–34 °C; germination of all fungi was 94% under these optimal conditions. However, immersion of the driest Bb, Ma, and Mac powders in warm water (33 °C) also resulted in high viabilities (95%, 89%, and 94%, respectively), and slow-rehydrated conidia also retained high viability (87%, 92%, and 83%, respectively) after immersion in ice-cold water (0.5 °C). Formulation of conidia in pure (non-emulsifiable) paraffinic oil provided considerable protection from imbibitional damage. This study underscores a need for establishing standard protocols for preparing aqueous suspensions of sensitive fungi for both research and commercial applications.  相似文献   
2.
Two hypotheses on the synthesis of the protectants glycerol and trehalose of the infective juveniles (IJs) of Steinernema carpocapsae during osmotic dehydration were tested and utilised to evaluate the function and importance of glycerol on survival of the nematodes during osmotic dehydration. This was achieved by comparing the changes in survival, morphology, behaviour and levels of glycerol, trehalose and permeated compounds of the IJs dehydrated in seven hypertonic solutions at two temperature regimes: (1) 5 °C for 15 days; and (2) 23 °C for 1 day followed by 5 °C for another 14 days. The results substantiate both hypotheses tested: (1) the permeability of the IJs to various compounds, such as sucrose or ethylene glycol, when they are dehydrated in hypertonic solutions of these compounds; and (2) suppression of the synthesis of protectant glycerol but not trehalose when IJs are dehydrated at low temperature. The results also showed that: (1) although trehalose was the preferred dehydration protectant, glycerol played an important role in rapidly balancing the osmotic pressure when IJs were exposed in hypertonic solutions; (2) the presence of glycerol was essential for the IJs to survive and function properly even under moderate osmotic dehydration, especially when IJs were dehydrated in salt solutions; and (3) some exogenous compounds permeated into IJs during osmotic dehydration such as ethylene glycol, may function in the same way as glycerol and significantly improve the survival and function of the IJs. The results indicate that each of the protectants glycerol and trehalose has a specific function and neither is replaceable by the other.  相似文献   
3.
With a view to gaining evidence on the mechanism by which D-trehalose is able to stabilise biomolecules towards dehydration (anhydrobiosis) and heat, L-trehalose has been prepared in order to allow comparative studies to be made. Little change can be induced in the ratio of the alpha,alpha-, alpha,beta-, beta,beta-1,1'-stereoisomers of the disaccharide formed from 2,3,4,6-tetra-O-benzyl-L-glucose by using different reaction procedures and by varying the reaction conditions. Benzyl 2,3,4,6-tetra-O-benzyl alpha- and beta-L-glucopyranoside are by-products in the trimethylsilyl trifluoromethanesulphonate mediated formation of the 1,1'-linked disaccharides.  相似文献   
4.
Aquaporin, AQP, is a channel protein that allows water to permeate across cell membranes. Larvae of the sleeping chironomid, Polypedilum vanderplanki, can withstand complete dehydration by entering anhydrobiosis, a state of suspended animation; however, the mechanism by which water flows out of the larval body during dehydration is still unclear. We isolated two cDNAs (PvAqp1 and PvAqp2) encoding water-selective aquaporins from the chironomid. When expressed in Xenopus oocytes, PvAQP1 and PvAQP2 facilitated permeation of water but not glycerol. Northern blots and in situ hybridization showed that expression of PvAqp1 was dehydration-inducible and ubiquitous whereas that of PvAqp2 was dehydration-repressive and fat body-specific. These data suggest distinct roles for these aquaporins in P. vanderplanki, i.e., PvAqp2 controls water homeostasis of fat body during normal conditions and PvAqp1 is involved in the removal of water during induction of anhydrobiosis.  相似文献   
5.
Respiration and fermentation were lower in active dry yeast (ADY) rehydrated at 0°C than in ADY rehydrated at 40°C. In agreement with other reports, it was found that membrane permeability increased during rehydration. In addition, ADY rehydrated at 0° did not reseal, even after hours of incubation at 40°C. Using 32P-nuclear magnetic resonance it was found that the cellular concentration of sugar phosphates, phosphate, pyrophosphate, NADH and ATP were lower in ADY rehydrated at 0°C. In addition, the phospholipid peak had a higher height to broadness ratio at 0°C than at 40°C, suggesting that membranes in the 0° sample were more disordered. The lower fermentation rate in ADY rehydrated at 0° could not be due solely to membrane permeation since addition of cofactors that leaked from these cells did not reactivate fermentation. In cell free extracts or in toluenized cells it was observed that some activities were modified after rehydration at 0°C. In the 40°C sample a lower activity of pyruvate decarboxylase and higher fructose-1,6-bisphosphatase and ATPase activities were detected. As a result, higher levels of ADP and pyruvate were found in the cell. Higher ADP levels could contribute to the higher fermentation rate of the cells rehydrated at 40°C. Enzyme modification might explain the low viability of ADY observed by a plating method, even in cells that were impermeable to a vital dye.Abbreviations ADY Active dry yeast - MES 2(N-morpholino)-ethanesulfonic acid  相似文献   
6.
Some organisms are able to survive the loss of almost all their body water content, entering a latent state known as anhydrobiosis. The sleeping chironomid (Polypedilum vanderplanki) lives in the semi-arid regions of Africa, and its larvae can survive desiccation in an anhydrobiotic form during the dry season. To unveil the molecular mechanisms of this resistance to desiccation, an anhydrobiosis-related Expressed Sequence Tag (EST) database was obtained from the sequences of three cDNA libraries constructed from P. vanderplanki larvae after 0, 12, and 36 h of desiccation. The database contained 15,056 ESTs distributed into 4,807 UniGene clusters. ESTs were classified according to gene ontology categories, and putative expression patterns were deduced for all clusters on the basis of the number of clones in each library; expression patterns were confirmed by real-time PCR for selected genes. Among up-regulated genes, antioxidants, late embryogenesis abundant (LEA) proteins, and heat shock proteins (Hsps) were identified as important groups for anhydrobiosis. Genes related to trehalose metabolism and various transporters were also strongly induced by desiccation. Those results suggest that the oxidative stress response plays a central role in successful anhydrobiosis. Similarly, protein denaturation and aggregation may be prevented by marked up-regulation of Hsps and the anhydrobiosis-specific LEA proteins. A third major feature is the predicted increase in trehalose synthesis and in the expression of various transporter proteins allowing the distribution of trehalose and other solutes to all tissues.  相似文献   
7.
We examined the influence of insect cadaver desiccation on the virulence and production of entomopathogenic nematodes (EPNs), common natural enemies of many soil-dwelling insects. EPNs are often used in biological control, and we investigated the feasibility of applying EPNs within desiccated insect cadavers. Desiccation studies were conducted using the factitious host, Galleria mellonella (Lepidoptera: Pyralidae, wax moth larvae) and three EPN species (Heterorhabditis bacteriophora ‘HB1’, Steinernema carpocapsae ‘All’, and Steinernema riobrave). Weights of individual insect cadavers were tracked daily during the desiccation process, and cohorts were placed into emergence traps when average mass losses reached 50%, 60%, and 70% levels. We tracked the proportion of insect cadavers producing infective juveniles (IJs), the number and virulence of IJs produced from desiccated insect cadavers, and the influence of soil water potentials on IJ production of desiccated insect cadavers. We observed apparent differences in the desiccation rate of the insect cadavers among the three species, as well as apparent differences among the three species in both the proportion of insect cadavers producing IJs and IJ production per insect cadaver. Exposure of desiccated insect cadavers to water potentials greater than −2.75 kPa stimulated IJ emergence. Among the nematode species examined, H. bacteriophora exhibited lower proportions of desiccated insect cadavers producing IJs than the other two species. Desiccation significantly reduced the number of IJs produced from insect cadavers. At the 60% mass loss level, however, desiccated insect cadavers from each of the three species successfully produced IJs when exposed to moist sand, suggesting that insect cadaver desiccation may be a useful approach for biological control of soil insect pests.  相似文献   
8.
Chen T  Bhowmick S  Sputtek A  Fowler A  Toner M 《Cryobiology》2002,44(3):1582-306
Although mixtures of HES and sugars are used to preserve cells during freezing or drying, little is known about the glass transition of HES, or how mixtures of HES and sugars vitrify. These difficulties may be due to the polydispersity between HES samples or differences in preparation techniques, as well as problems in measuring the glass transition temperature (T(g)) using differential scanning calorimetry (DSC). In this report, we examine the T(g) of mixtures of HES and trehalose sugar with <1% moisture content using DSC measurements. By extrapolating these measurements to pure HES using the Gordon-Taylor and Fox equations, we were able to estimate the T(g) of our HES sample at 44 degrees C. These results were additionally confirmed by using mixtures of glucose-HES which yielded a similar extrapolated T(g) value. Our approach to estimating the glass transition temperature of HES may be useful in other cases where glass transitions are not easily identified.  相似文献   
9.
10.
The environmental physiology of Antarctic terrestrial nematodes: a review   总被引:10,自引:1,他引:9  
The environmental physiology of terrestrial Antarctic nematodes is reviewed with an emphasis on their cold-tolerance strategies. These nematodes are living in one of the most extreme environments on Earth and face a variety of stresses, including low temperatures and desiccation. Their diversity is low and declines with latitude. They show resistance adaptation, surviving freezing and desiccation in a dormant state but reproducing when conditions are favourable. At high freezing rates in the surrounding medium the Antarctic nematode Panagrolaimus davidi freezes by inoculative freezing but can survive intracellular freezing. At slow freezing rates this nematode does not freeze but undergoes cryoprotective dehydration. Cold tolerance may be aided by rapid freezing, the production of trehalose and by an ice-active protein that inhibits recrystallisation. P. davidi relies on slow rates of water loss from its habitat, and can survive in a state of anhydrobiosis, perhaps aided by the ability to synthesise trehalose. Teratocephalus tilbrooki and Ditylenchus parcevivens are fast-dehydration strategists. Little is known of the osmoregulatory mechanisms of Antarctic nematodes. Freezing rates are likely to vary with water content in Antarctic soils. Saturated soils may produce slow freezing rates and favour cryoprotective dehydration. As the soil dries freezing rates may become faster, favouring freezing tolerance. When the soil dries completely the nematodes survive anhydrobiotically. Terrestrial Antarctic nematodes thus have a variety of strategies that ensure their survival in a harsh and variable environment. We need to more fully understand the conditions to which they are exposed in Antarctic soils and to apply more natural rates of freezing and desiccation to our studies.Communicated by: I.D. Hume  相似文献   
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