Surface structure changes of rat adipocytes during lypolysis stimulated by various lypolysis stimulated by various lypolytic agents

A qualitative and quantitative electron microscopic study was performed on rat adipocytes during stimulation of lipolysis by various agents. Scanning electron microscopy of control cells revealed a spherical cell with a textured glycocalyx surface exhibiting small irregular projections. Globular surface evaginations or protrusions measuring 8-18 μM in diameter were seen on cell hemispheres, and there was an average of one protrusion for every two hemispheres examined. Distribution analysis showed that 60 percent of the hemispheres had no protrusions, and 25, 10, and 5 percent of the hemispheres had one, two or three protrusions, respectively. Thin-section and freeze- fracture electron microscopy of the protrusions showed a small triglyceride droplet surrounded by a thin cytoplasmic rim that was continuous with the main cytoplasmic matrix. The glycocalyx coating and plasma membrane extended from the cell surface onto, and over, the protrusion. Scanning microscopy of cells stimulated by lipolytic agents, including epinephrine, adrenocorticotropic hormone, theophylline, and dibutyryl cyclic AMP, revealed a dose-dependent increase in the number of protrusions per cell hemisphere. Maximal concentrations of lipolytic hormones cuase an average 2.5-fold increase in the number of protrusions per hemisphere without changing the average size of the protrusions. Only 40 percent of the stimulated cell hemispheres exhibited no protrusions; over 15 percent of the cells contained three or more; and a number of the protrusions were multilobulate. Insulin prevented the increase in the number of protrusions and the change in distribution caused by the lipolytic hormones but did not prevent the increase caused by theophylline and dibutryl cyclic AMP. The data suggest that the protrusions are a structural feature of the cell and may be related to the lypolytic pathway. These observations may help explain some of the discrepant biochemical data relating to hormonal stimulation of lipolysis.     

On the structure of the Z pseudo-organ in Xiphinema diversicaudatum

The structure of the Z pseudo-organ in Xiphinema diversicaudatum consists of a muscular mass of about 80 cells arranged in rings of four cells each. These cells have peripheral nuclei and are connected with a glandular monolayered epithelium, which lines the lumen of the Z pseudo-organ. Globular bodies originate from the membranes of the epithelial tissue. They consist of a series of closed vesicles containing secretions, and of tubules through which the secretions flow into the lumen. The globular bodies have a helicoidal distribution within the lumen of the Z pseudo-organ which presumably slows the passage of the egg. Enzymatic digestion, in vivo, indicates that the secretion consists of acid and basic proteins involved in egg shell formation.     

Nitrogen budget of a subarctic stream altered by beaver (Castor canadensis)

Beaver (Castor canadensis) influence stream ecosystems through their wood cutting and dam building activities. To quantify this influence we have used measured rates of nitrogen dynamics to construct a nitrogen budget for a section of a second order stream in eastern Québec and a beaver dam in that stream. The budget demonstrates the importance of sediment accumulations and an expanded wetted area to the annual nitrogen economy and to pathways of nitrogen cycling. Major changes after impoundment (per unit area) include a reduction in allochthonous nitrogen and an increase in nitrogen fixation by sediment microbes. Overall, the beaver-modified section accumulated 10³ times more nitrogen than before alteration. The ecosystem implications of beaver activity suggest that current concepts of patterns and processes in running waters require modification.Research support by NSF grant DEB 81-05677 and the Woods Hole Oceanographic Institution. this is Contribution No. 5565 from the Woods Hole Oceanographic Institution and No. 88 from the Institution's Matamek Research Station     

Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems

Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the growing season at all sites. Nitrate-N pools in soil were generally smaller than ammonium-N pools and monthly nitrification rates were less variable than net N mineralization rates. Nitrate supplied most of the N taken up annually by vegetation at 8 of the 9 sites. Furthermore, despite the large fluctuations in ammonium-N pools and monthly net N mineralization, nitrate was taken up at relatively uniform rates during the growing season at most sites.     

Soil warming accelerates decomposition of fine woody debris

Aims

There is evidence that increased N inputs to boreal forests, via atmospheric deposition or intentional fertilization, may impact negatively on ectomycorrhizal (ECM) fungi leading to a reduced flux of plant-derived carbon (C) back to the atmosphere via ECM. Our aim was to investigate the impact of N fertilization of a Pinus sylvestris (L.) forest stand on the return of recently photoassimilated C via the ECM component of soil respiration.

Methods

We used an in situ, large-scale, ¹³C-CO₂ isotopic pulse labelling approach and monitored the ¹³C label return using soil gas efflux chambers placed over three different types of soil collar to distinguish between heterotrophic (R_H), autotrophic (R_A; partitioned further into contributions from ECM hyphae and total R_A) and total (R_S) soil respiration.

Results

The impact of N fertilization was to significantly reduce R_A, particularly respiration via extramatrical ECM hyphae. ECM hyphal flux in control plots showed substantial spatial variability, resulting in mean flux estimates exceeding estimates of total R_A, while ECM contributions to R_A in N treated plots were estimated at around 30%.

Conclusion

Significant impacts on soil C cycling may be caused by reduced plant C allocation to ECM fungi in response to increased N inputs to boreal forests; ecosystem models so far lack this detail.     

Soil warming alters nitrogen cycling in a New England forest: implications for ecosystem function and structure

Global climate change is expected to affect terrestrial ecosystems in a variety of ways. Some of the more well-studied effects include the biogeochemical feedbacks to the climate system that can either increase or decrease the atmospheric load of greenhouse gases such as carbon dioxide and nitrous oxide. Less well-studied are the effects of climate change on the linkages between soil and plant processes. Here, we report the effects of soil warming on these linkages observed in a large field manipulation of a deciduous forest in southern New England, USA, where soil was continuously warmed 5°C above ambient for 7 years. Over this period, we have observed significant changes to the nitrogen cycle that have the potential to affect tree species composition in the long term. Since the start of the experiment, we have documented a 45% average annual increase in net nitrogen mineralization and a three-fold increase in nitrification such that in years 5 through 7, 25% of the nitrogen mineralized is then nitrified. The warming-induced increase of available nitrogen resulted in increases in the foliar nitrogen content and the relative growth rate of trees in the warmed area. Acer rubrum (red maple) trees have responded the most after 7 years of warming, with the greatest increases in both foliar nitrogen content and relative growth rates. Our study suggests that considering species-specific responses to increases in nitrogen availability and changes in nitrogen form is important in predicting future forest composition and feedbacks to the climate system.     

Heterologous expression of pentalenene synthase (PSS) from Streptomyces UC5319 in Xanthophyllomyces dendrorhous

For the first time, the pentalenene synthase (PSS) gene from Streptomyces UC5319 was expressed in Xanthophyllomyces dendrorhous, a native producer of astaxanthin. For the expression of the gene and the concurrent knock out of the native crtE or crtYB genes, two new vectors were engineered and used for the transformation of the wild-type strain of X. dendrorhous. The transformations resulted in white colonies, showing a complete shutdown of the carotenoid production. Furthermore, an additional vector was constructed for the insertion of the PSS gene in the rDNA of the yeast. All the mutant strains produce the sesquiterpene pentalenene and show no difference in growth when compared to the wild-type strain. In this report, we demonstrate that X. dendrorhous is a suitable host for the expression of heterologous terpene cyclases and for the production of foreign terpene compounds.     

Synthesis of the first sulfur-35-labeled hERG radioligand

The synthesis of the first high specific activity S-35-labeled hERG radioligand, [(35)S]MK-0499, for use in HTS assays of drug candidates for hERG interaction is described. The radioligand is prepared by [(35)S]sulfonylation of a high diastereomeric excess (de) aniline precursor prepared from unlabeled MK-0499.