Freezing tolerance of ectomycorrhizal fungi in pure culture

The ability to survive freezing and thawing is a key factor for the existence of life forms in large parts of the world. However, little is known about the freezing tolerance of mycorrhizal fungi and their role in the freezing tolerance of mycorrhizas. Threshold temperatures for the survival of these fungi have not been assessed experimentally. We grew isolates of Suillus luteus, Suillus variegatus, Laccaria laccata, and Hebeloma sp. in liquid culture at room temperature. Subsequently, we exposed samples to a series of temperatures between +5°C and −48°C. Relative electrolyte leakage (REL) and re-growth measurements were used to assess the damage. The REL test indicated that the lethal temperature for 50% of samples (LT₅₀) was between −8.3°C and −13.5°C. However, in the re-growth experiment, all isolates resumed growth after exposure to −8°C and higher temperatures. As many as 64% of L. laccata samples but only 11% in S. variegatus survived −48°C. There was no growth of Hebeloma and S. luteus after exposure to −48°C, but part of their samples survived −30°C. The fungi tolerated lower temperatures than was expected on the basis of earlier studies on fine roots of ectomycorrhizal trees. The most likely freezing tolerance mechanism here is tolerance to apoplastic freezing and the concomitant intracellular dehydration with consequent concentrating of cryoprotectant substances in cells. Studying the properties of fungi in isolation promotes the understanding of the role of the different partners of the mycorrhizal symbiosis in the freezing tolerance.     

Simultaneous measurement of retinol, alpha-tocopherol and six carotenoids in human plasma by using an isocratic reversed-phase HPLC method

A simple and sensitive isocratic reversed-phase high-performance liquid chromatography (HPLC) method for simultaneous determination of retinol, alpha-tocopherol and six carotenoids in human plasma was described. Sample preparation of the earlier published method was further developed by addition of ultrapure water, which enabled aqueous layer to freeze facilitating phase separation without pipetting thus also improving precision of the method. Developed method appeared to be less laborious and time consuming compared to the traditional extraction methods, which require removal of organic layer by pipetting. The recoveries (absolute and relative) were between 80% and 103%. The intra-assay CVs were 1.1-4.0% (normal level) and 3.3-9.0% (low level). Inter-assay CVs were 5.3-8.8%. Reference method for all these analytes was not available, but a comparison with another published method was carried out. The results of the comparison matched satisfactorily. The method is used routinely in our laboratory in a large population-based study.     

Predation on two vole species by a shared predator: antipredatory response and prey preference

In prey communities with shared predators, variation in prey vulnerability is a key factor in shaping community dynamics. Conversely, the hunting efficiency of a predator depends on the prey community structure, preferences of the predator and antipredatory behavioural traits of the prey. We studied experimentally, under seminatural field conditions, the preferences of a predator and the antipredatory responses of prey in a system consisting of two Myodes species of voles, the grey-sided vole (M. rufocanus Sund.) and the bank vole (M. glareolus Schreb.), and their specialist predator, the least weasel (Mustela nivalis nivalis L.). To quantify the preference of the weasels, we developed a new modelling framework that can be used for unbalanced data. The two vole species were hypothesised to have different habitat-dependent vulnerabilities. We created two habitats, open and forest, to provide different escape possibilities for the voles. We found a weak general preference of the weasels for the grey-sided voles over the bank voles, and a somewhat stronger preference specifically in open habitats. The weasels clearly preferred male grey-sided voles over females, whereas in bank voles, there was no difference. The activity of voles changed over time, so that voles increased their movements immediately after weasel introduction, but later adjusted their movements to times of lowered predation risk. Females that were more active had an elevated mortality risk, whereas in the case of males, the result was the opposite. We conclude that, in vulnerability to predation, the species- or habitat-specific characteristics of these prey species are playing a minor role compared to sex-specific characteristics.     

What are definitions of life good for? Transdisciplinary and other definitions in astrobiology

The attempt to define life has gained new momentum in the wake of novel fields such as synthetic biology, astrobiology, and artificial life. In a series of articles, Cleland, Chyba, and Machery claim that definitions of life seek to provide necessary and sufficient conditions for applying the concept of life—something that such definitions cannot, and should not do. We argue that this criticism is largely unwarranted. Cleland, Chyba, and Machery approach definitions of life as classifying devices, thereby neglecting their other epistemic roles. We identify within the discussions of the nature and origin of life three other types of definitions: theoretical, transdisciplinary, and diagnostic definitions. The primary aim of these definitions is not to distinguish life from nonlife, although they can also be used for classificatory purposes. We focus on the definitions of life within the budding field of astrobiology, paying particular attention to transdisciplinary definitions, and diagnostic definitions in the search for biosignatures from other planets.     

Corrigendum: Effect of soil temperature on nutrient allocation and mycorrhizas in Scots pine seedlings

(Plant and Soil 239: 173–185, 2002.)An inadvertent omission of figure captions occurred in the article by Domisch et al. Please find the correct captions below: Figure 1. Relationship between the numbers of root tips identified by the WinRHIZO programme and counted manually under a dissecting microscope (n = 128). Figure 2. (A) N, (B) P and (C) Ca content and allocation within different parts of the seedlings at 3, 6 and 9 weeks and at soil temperatures of 5, 9, 13 and 17°C. The P and Ca content of the new roots in all harvests at 5 °C and in the first harvest at 9 °C is estimated (see text for details) (n = 14). Standard errors are indicated. Figure 3. (A) Al and (B) Fe content and allocation within different parts of the seedlings at 3, 6 and 9 weeks and at soil temperatures of 5, 9, 13 and 17 °C. The Al and Fe content of the new roots in all harvests at 5 °C and in the first harvest at 9 °C soil temperature is estimated (see text for details) (n=14). Standard errors are indicated. Figure 4. (A) Total numbers of tips of new roots and (B) their relative distributions within the groups at 3, 6 and 9 weeks and at soil temperatures of 5, 9, 13 and 17 °C (n = 14; ± standard errors) Figure 5. (A) Total numbers of mycorrhiza of new roots and (B) their relative distributions within the groups at 3, 6 and 9 weeks and at soil temperatures of 5, 9, 13 and 17 °C (n = 14; ± standard errors).     

Long-term dynamics of voles and lemmings at the timberline and above the willow limit as a test of hypotheses on trophic interactions

We have monitored population fluctuations of microtine rodents since 1977 in two habitat complexes in Finnmark, northernmost Norway - a low arctic plains landscape, with patches of willow scrubland embedded in lichen-dwarf birch tundra, and in adjacent highlands, occupied by scrub-free heaths, snow-beds and bogs. In the plains landscape, voles were cyclic, with a period of five years, and with wave-like density fluctuations. This pattern is consistent with time trajectory of prey in a predator-prey limit cycle. Autoregression analysis implies that the prey pattern is cleanest in the most productive plains habitats, while dynamics in the prevailing heath and bog habitats are governed by two significant lags, implying that even vole-plant interactions count. In the highlands, lemmings had two outbreaks, characterized by J-shaped growth curves, and separated by long periods of low density. The fluctuation pattern of lemmings in highlands was consistent with the predicted time trajectory of a predator. The implications of time trajectories are corroborated by direct evidence on microtine impacts upon the vegetation and on spatial patterns in predator activity. Even the strong dispersal tendency of lemmings during population peaks is consistent with the conjecture that they are adapted to play the role of a predator in a sustained predator-prey cycle. As a whole, the pattern supports T. Oksanen's modification of the hypothesis of exploitation ecosystems, where both local productivity and the structure of the landscape are taken in account.     

Inactivation of mouse transmembrane prolyl 4-hydroxylase increases blood brain barrier permeability and ischemia-induced cerebral neuroinflammation

Hypoxia-inducible factor prolyl 4-hydroxylases (HIF-P4Hs) regulate the hypoxic induction of >300 genes required for survival and adaptation under oxygen deprivation. Inhibition of HIF-P4H-2 has been shown to be protective in focal cerebral ischemia rodent models, while that of HIF-P4H-1 has no effects and inactivation of HIF-P4H-3 has adverse effects. A transmembrane prolyl 4-hydroxylase (P4H-TM) is highly expressed in the brain and contributes to the regulation of HIF, but the outcome of its inhibition on stroke is yet unknown. To study this, we subjected WT and P4htm^−/− mice to permanent middle cerebral artery occlusion (pMCAO). Lack of P4H-TM had no effect on lesion size following pMCAO, but increased inflammatory microgliosis and neutrophil infiltration was observed in the P4htm^−/− cortex. Furthermore, both the permeability of blood brain barrier and ultrastructure of cerebral tight junctions were compromised in P4htm^−/− mice. At the molecular level, P4H-TM deficiency led to increased expression of proinflammatory genes and robust activation of protein kinases in the cortex, while expression of tight junction proteins and the neuroprotective growth factors erythropoietin and vascular endothelial growth factor was reduced. Our data provide the first evidence that P4H-TM inactivation has no protective effect on infarct size and increases inflammatory microgliosis and neutrophil infiltration in the cortex at early stage after pMCAO. When considering HIF-P4H inhibitors as potential therapeutics in stroke, the current data support that isoenzyme-selective inhibitors that do not target P4H-TM or HIF-P4H-3 would be preferred.     

Pikas (Ochotona princeps : Lagomorpha) as allogenic engineers in an alpine ecosystem

Pikas (Ochotona princeps: Lagomorpha) build caches of vegetation (“haypiles”), which serve as a food source during winter in alpine and subalpine habitats. Haypiles appear to degrade over time and form patches of nutrient-rich soils in barren talus and scree areas. We sampled soils underneath and next to haypiles, and plants growing on and near haypiles in an alpine cirque in northwestern Wyoming, USA, to determine the effects of pika food caches on N, C, and C/N ratios in soils and plants. We found that (1) haypile soils had significantly higher carbon and nitrogen levels and lower C/N ratios than both adjacent soils and soils in the general study area, (2) two of three plant species tested (Polemonium viscosum and Oxyria digyna) had significantly higher levels of tissue percent N when growing on haypile soils, and (3) total standing plant biomass at the study site increased with soil percent N suggesting that vegetation was nitrogen limited. Pikas may therefore function as allogenic ecosystem engineers by modulating nutrient availability to plants. Received: 5 July 1997 / Accepted: 30 November 1997     

Osteoblast Recruitment and Bone Formation Enhanced by Cell Matrix–associated Heparin-binding Growth-associated Molecule (HB-GAM)

Bone has an enormous capacity for growth, regeneration, and remodeling. This capacity is largely due to induction of osteoblasts that are recruited to the site of bone formation. The recruitment of osteoblasts has not been fully elucidated, though the immediate environment of the cells is likely to play a role via cell– matrix interactions. We show here that heparin-binding growth-associated molecule (HB-GAM), an extracellular matrix–associated protein that enhances migratory responses in neurons, is prominently expressed in the cell matrices that act as target substrates for bone formation. Intriguingly, N-syndecan, which acts as a receptor for HB-GAM, is expressed by osteoblasts/osteoblast precursors, whose ultrastructural phenotypes suggest active cell motility. The hypothesis that HB-GAM/N-syndecan interaction mediates osteoblast recruitment, as inferred from developmental studies, was tested using osteoblast-type cells that express N-syndecan abundantly. These cells migrate rapidly to HB-GAM in a haptotactic transfilter assay and in a migration assay where HB-GAM patterns were created on culture wells. The mechanism of migration is similar to that previously described for the HB-GAM–induced migratory response of neurons. Our hypothesis that HB-GAM/N-syndecan interaction participates in regulation of osteoblast recruitment was tested using two different in vivo models: an adjuvant-induced arthritic model and a transgenic model. In the adjuvant-induced injury model, the expression of HB-GAM and of N-syndecan is strongly upregulated in the periosteum accompanying the regenerative response of bone. In the transgenic model, the HB-GAM expression is maintained in mesenchymal tissues with the highest expression in the periosteum. The HB-GAM transgenic mice develop a phenotype characterized by an increased bone thickness. HB-GAM may thus play an important role in bone formation, probably by mediating recruitment and attachment of osteoblasts/osteoblast precursors to the appropriate substrates for deposition of new bone.     

Exploitation ecosystems in heterogeneous habitat complexes II: Impact of small-scale heterogeneity on predator-prey dynamics

Summary The model of exploitation ecosystems was re-analysed, assuming that habitat patches are so small that they form only parts of the home range of an individual predator. For habitat complexes where productive patches abound, the results suggested that predation will strongly spill over from productive patches, which set the tune for population dynamics within the whole landscape, to barren ones. This result conforms to the one obtained by T. Oksanen by assuming despotic habitat choice and essentially larger patch sizes. For habitat complexes heavily dominated by the barren habitat, spillover predation was predicted to be weak, as was the case in her large patch model. Unlike in her analysis, however, predation pressure was substantially reduced also within the productive habitat. In habitat complexes where patches are so small that they are exploited in a fine-grained manner, predation pressure was always found to be more intense in the barren habitat, contrary to the predictions of the original model of exploitation ecosystems. This analysis thus suggests that their model is applicable mainly on the landscape level. On the level of individual habitats, the applicability of their results depends on the habitat configuration (at its best for the prevailing habitat of the landscape and for moderate-sized patches of an essentially more productive habitat) and generally decreases with decreasing patch sizes.