鼠李糖脂的表面化学和生物合成及其在垃圾堆肥中的应用展望

鼠李糖脂是生物表面活性剂中一类非常重要而应用广泛的微生物发酵产物,在环境污染修复中需求量越来越多。针对近十年来国内外对鼠李糖脂生物表面活性剂的研究,较系统地总结了其化学结构、性质、生物合成机理及产量调节方法,及大规模生产鼠李糖脂的基础研究工作,并对其在城市生活垃圾堆肥中的应用做了展望。     

Leaf productivity along a precipitation gradient in lowland Panama: patterns from leaf to ecosystem

Moisture availability has the potential to affect tropical forest productivity at scales ranging from leaf to ecosystem. We compared data for leaf photosynthetic, chemical and structural traits of canopy trees, litterfall production and seasonal availability of soil water at four sites across a precipitation gradient (1,800–3,500 mm year^–1) in lowland Panamanian forest to determine how productivity at leaf and ecosystem scales may be related. We found stronger seasonality in soil water potential at drier sites. Values were close to zero at all sites during the wet season and varied between a minimum of –2.5 MPa and –0.3 MPa at the driest and wettest sites, respectively, during the dry season. Leaf photosynthesis and nitrogen concentration decreased with increasing precipitation, whereas leaf thickness increased with increasing precipitation. Leaf toughness and fiber/N ratios increased with increasing precipitation indicating reduced nutritional content and palatability with precipitation. Seasonality of litter production and quality decreased with increasing precipitation, but the amount of litterfall produced was not substantially different among sites. It appears that in Neotropical forest, moisture availability is associated with leaf photosynthetic and defensive traits that influence litterfall timing and quality. Therefore, variation in leaf physiological traits has the potential to influence decomposition and nutrient cycling through effects on litter quality.     

Oxygen measurements in brain stem slices exposed to normobaric hyperoxia and hyperbaric oxygen.

We previously reported (J Appl Physiol 89: 807-822, 2000) that < or =10 min of hyperbaric oxygen (HBO(2); < or = 2,468 Torr) stimulates solitary complex neurons. To better define the hyperoxic stimulus, we measured PO(2) in the solitary complex of 300-microm-thick rat medullary slices, using polarographic carbon fiber microelectrodes, during perfusion with media having PO(2) values ranging from 156 to 2,468 Torr. Under control conditions, slices equilibrated with 95% O(2) at barometric pressure of 1 atmospheres absolute had minimum PO(2) values at their centers (291 +/- 20 Torr) that were approximately 10-fold greater than PO(2) values measured in the intact central nervous system (10-34 Torr). During HBO(2), PO(2) increased at the center of the slice from 616 +/- 16 to 1,517 +/- 15 Torr. Tissue oxygen consumption tended to decrease at medium PO(2) or = 1,675 Torr to levels not different from values measured at PO(2) found in all media in metabolically poisoned slices (2-deoxy-D-glucose and antimycin A). We conclude that control medium used in most brain slice studies is hyperoxic at normobaric pressure. During HBO(2), slice PO(2) increases to levels that appear to reduce metabolism.     

Nonglucosylated oligosaccharides are transferred to protein in MI8-5 Chinese hamster ovary cells

A CHO mutant MI8-5 was found to synthesize Man9-GlcNAc2-P-P-dolichol rather than Glc3Man9GlcNAc2-P-P-dolichol as the oligosaccharide-lipid intermediate in N-glycosylation of proteins. MI8-5 cells were incubated with labeled mevalonate, and the prenol was found to be dolichol. The mannose-labeled oligosaccharide released from oligosaccharide-lipid of MI8-5 cells was analyzed by HPLC and alpha-mannosidase treatment, and the data were consistent with a structure of Man9GlcNAc2. In addition, MI8-5 cells did not incorporate radioactivity into oligosaccharide- lipid during an incubation with tritiated galactose, again consistent with MI8-5 cells synthesizing an unglucosylated oligosaccharide-lipid. MI8-5 cells had parental levels of glucosylphosphoryldolichol synthase activity. However, in two different assays, MI8-5 cells lacked dolichol- P-Glc:Man9GlcNAc2-P-P-dolichol glucosyltransferase activity. MI8-5 cells were found to synthesize glucosylated oligosaccharide after they were transfected with Saccharomyces cerevisiae ALG 6, the gene for dolichol-P-Glc:Man9GlcNAc2-P-P-dolichol glucosyltransferase. MI8-5 cells were found to incorporate mannose into protein 2-fold slower than parental cells and to approximately a 2-fold lesser extent.      

Oxygen isotope ratio stratification in a tropical moist forest

Summary Oxygen isotope ratios were determined in leaf cellulose from two plant species at Barro Colorado (Republic of Panama) in 4 different plots, two of which were undergoing an irrigation treatment during the dry season. There is a gradient in ¹⁸O values of leaf cellulose from the understory to canopy leaves, reflecting the differences in relative humidity between these two levels of the forest. This gradient is most pronounced in irrigated plots. For irrigated plots there was a highly significant correlation between ¹⁸O and ¹³C values, which was not observed in control plots. This relationship can be explained by humidity controlling stomatal conductance. Low humidity affects ¹⁸O values of leaf water during photosynthesis, which isotopically labels cellulose during its synthesis. Low humidity also decreases stomatal conductance, which affects discrimination against carbon-13 by photosynthetic reactions, thus affecting the ¹³C values of photosynthates. WUE values calculated by using plant carbon and oxygen isotope ratios were similar to those observed with gas exchange measurements in other tropical and temperate area. Thus the concurrent analysis of carbon and oxygen isotope ratios of leaf material can potentially be useful for long term estimation of assimilation and evapotranspiration regimes of plants.     

Interannual variability of seasonal succession events in a temperate lake and its relation to temperature variability

The assessment of possible implications of anthropogenic climate change requires the evaluation of results obtained with complex climate models. Here we considered the problem of assessing the impact of climate variability on successional events in a lake (Plußsee) of the temperate region between January and May. We first established a statistical link between large-scale air temperature, at about 1500 m height, and the local temperature, in order to bridge the spatial gap of information obtained from global climate models and local climate which forces processes in the lake. Secondly, the local temperatures were statistically related to biologically induced dynamic features in the lake, derived from Secchi depths readings (as integrated measures). The observed relationships were compared with results from a phyto- and zooplankton population-dynamic model run under different temperature regimes. The local temperatures approximated closely the large-scale temperature. The timing of phyto- and zooplankton maxima (clearwater phase) were negatively related to the temperature. Thus, with a temperature increase both occurred earlier. The intensity of the spring algal maximum was negatively related to its timing, whereas no clear relation between the timing and intensity of the clearwater phase (zooplankton maximum) could be obtained.     

GC-1 mRHBDD1 knockdown spermatogonia cells lose their spermatogenic capacity in mouse seminiferous tubules

Background  

Apoptosis is important for regulating spermatogenesis. The protein mRHBDD1 (mouse homolog of human RHBDD1)/rRHBDD1 (rat homolog of human RHBDD1) is highly expressed in the testis and is involved in apoptosis of spermatogonia. GC-1, a spermatogonia cell line, has the capacity to differentiate into spermatids within the seminiferous tubules. We constructed mRHBDD1 knockdown GC-1 cells and evaluated their capacity to differentiate into spermatids in mouse seminiferous tubules.     

Cloning and expression analysis of two distinct HIF-alpha isoforms – gcHIF-1alpha and gcHIF-4alpha – from the hypoxia-tolerant grass carp,Ctenopharyngodon idellus

Background  

Hypoxia-inducible factors (HIFs) are involved in adaptive and survival responses to hypoxic stress in mammals. In fish, very little is known about the functions of HIFs.