Isozyme variation inBulnesia retama,B. schickendantzii andB. foliosa (Zygophyllaceae)

The genetic variation between two allopatric populations ofBulnesia retama and that ofB. schickendantzii andB. foliosa was investigated. The Peruvian population ofB. retama showed low values of P (0.117) and He (0.057) compared to those in the Argentine population with P = 0.59 and He = 0.269;B. schickendantzii showed P = 0.54 andB. foliosa P = 0.17. Genetic identity between the latter was 0.836 and between the allopatric populations ofB. retama was 0.89; the Peruvian population had reduced allelic variation per locus (A = 1.176) in comparison to the Argentine population (A = 1.955). The values of A, P, He andWright's fixation indices suggest that the Peruvian population could have originated from a single or very few migrants from southern latitudes (founder effect).     

Molecular Cloning, Genomic Organization, and Expression of a Testicular Isoform of Hormone-Sensitive Lipase

By catalyzing the rate-limiting step in adipose tissue lipolysis, hormone-sensitive lipase (HSL) is an important regulator of energy homeostasis. The role and importance of HSL in tissues other than adipose are poorly understood. We report here the cloning and expression of a testicular isoform, designated HSL_tes. Due to an addition of amino acids at the NH₂-termini, rat and human HSL_tesconsist of 1068 and 1076 amino acids, respectively, compared to the 768 and 775 amino acids, respectively, of the adipocyte isoform (HSL_adi). A novel exon of 1.2 kb, encoding the human testis-specific amino acids, was isolated and mapped to the HSL gene, 16 kb upstream of the exons encoding HSL_adi. The transcribed mRNA of 3.9 kb was specifically expressed in testis. No significant similarity with other known proteins was found for the testis-specific sequence. The amino acid composition differs from the HSL_adisequence, with a notable hydrophilic character and a high content of prolines and glutamines. COS cells, transfected by the 3.9-kb human testis cDNA, expressed a protein of the expected molecular mass (M_r≈ 120,000) that exhibited catalytic activity similar to that of HSL_adi. Immunocytochemistry localized HSL to elongating spermatids and spermatozoa; HSL was not detected in interstitial cells.     

Proliferative and morphological changes induced by vanadium compounds on Swiss 3T3 fibroblasts

Vanadium compounds are shown to have a mitogenic effect on fibroblast cells. The effects of vanadate, vanadyl and pervanadate on the proliferation and morphological changes of Swiss 3T3 cells in culture are compared. Vanadium derivatives induced cell proliferation in a biphasic manner, with a toxic-like effect at doses over 50mM, after 24h of incubation. Vanadyl and vanadate were equally potent at 2.5–10mM. At 50mM vanadate inhibited cell proliferation, whereas slight inhibition was observed at 100mM of vanadyl. At 10mM pervanadate was as potent as vanadate and vanadyl in stimulating fibroblast proliferation, but no effect was observed at lower concentrations. A pronounced cytotoxic-like effect was induced by pervanadate at 50mM. All of these effects were accompanied by morphological changes: transformation of fibroblast shape from polygonal to fusiform; retraction with cytoplasm condensation; and loss of lamellar processes. The magnitude of these transformations correlates with the potency of vanadium derivatives to induce a cytotoxic-like effect: pervanadate>vanadate>vanadyl. These data suggest that the oxidation state and coordination geometry of vanadium determine the degree of the cytotoxicity.     

Carbon sequestration rates in organic layers of boreal and temperate forest soils — Sweden as a case study

Aim The aim of this work was to estimate C sequestration rates in the organic matter layer in Swedish forests. Location The region encompassed the forested area (23 × 10⁶ ha) of Sweden ranging from about 55° N to 69° N. Methods We used the concept of limit values to estimate recalcitrant litter remains, and combined it with amount of litter fall. Four groups of tree species were identified (pine, spruce, birch and ‘other deciduous species’). Annual actual evapotranspiration (AET) was estimated for 5 × 5 km grids covering Sweden. For each grid, data of forested area and main species composition were available. The annual input of foliar litter into each grid was calculated using empirical relationships between AET and foliar litter fall in the four groups. Litter input was combined with average limit values for decomposition for the four groups of litter, based on empirical data. Finally, C sequestration rate was calculated using a constant factor of the C concentration in the litter decomposed to the limit value, thus forming soil organic matter (SOM). Results We obtained a value of 4.8 × 10⁶ metric tons of C annually sequestered in SOM in soils of mature forests in Sweden, with an average of 180 kg ha^?1 and a range from 40 to 410 kg ha^?1. Norway spruce forests accumulated annually an average of 200 kg C ha^?1. The pine and birch groups had an average of 150 kg ha^?1 and for the group of other deciduous trees, which is limited to south Sweden, the C sequestration was around 400 kg ha^?1. Conclusions There is a clear C sequestration gradient over Sweden with the highest C sequestration in the south‐west, mainly corresponding to the gradient in litter fall. The limit‐value method appears useful for scaling up to a regional level to describe the C sequestration in SOM. A development of the limit value approach in combination with process‐orientated dynamic models may have a predictive value.     

The enhancement of invasion ability of an annual grass by its fungal endophyte depends on recipient community structure

Most terrestrial plants establish symbiotic associations with microorganisms that enable them to overcome abiotic or biotic filters in ecosystems. Here we investigated how aerial mutualisms involving invasive species may affect the recipient community’s structure. We hypothesized that the endophyte Epichloë occultans enhances the ability of Lolium multiflorum to establish and colonize, but that success would depend on the structure and invasion resistance of the recipient grassland community. Seeds of L. multiflorum with high (E+) and low (E?) endophyte incidence were sown in plots located in grasslands with or without recent grazing history. Relative cover of L. multiflorum and floristic groups was determined during the growing season. Whereas we did not detect any endophyte effect in sites with grazing history, L. multiflorum cover was 63 % in E+ and 27 % in E? plots in sites without grazing history. As cover of L. multiflorum increased in these sites, the cover of warm- and cool-season grasses decreased in spring, with that of warm-season grasses continuing to decrease in summer. These decreases corresponded to 1.9, 3.7 and 1.6 %, for every % increase of L. multiflorum cover. Path analysis and posterior modelling predicted a greater impact of the endophyte on L. multiflorum cover than of seed addition when resident L. multiflorum cover was ≤20 %. This effect decreased asymptotically as L. multiflorum cover increased beyond 20 %. Our results suggest that the endophyte may boost the invasion ability of L. multiflorum particularly in natural grassland without grazing history with potential longer-term consequences for community structure and dynamics.     

Endophytic colonization of sugarcane (Saccharum officinarum) by the novel diazotrophs Shinella sp. UYSO24 and Enterobacter sp. UYSO10

Plant and Soil - Sugarcane is a multipurpose crop mostly used in Uruguay for bioethanol production. It requires high amounts of N fertilization for optimal growth, which causes environmental...     

R4496C RyR2 mutation impairs atrial and ventricular contractility

Ryanodine receptor (RyR2) is the major Ca²⁺ channel of the cardiac sarcoplasmic reticulum (SR) and plays a crucial role in the generation of myocardial force. Changes in RyR2 gating properties and resulting increases in its open probability (P_o) are associated with Ca²⁺ leakage from the SR and arrhythmias; however, the effects of RyR2 dysfunction on myocardial contractility are unknown. Here, we investigated the possibility that a RyR2 mutation associated with catecholaminergic polymorphic ventricular tachycardia, R4496C, affects the contractile function of atrial and ventricular myocardium. We measured isometric twitch tension in left ventricular and atrial trabeculae from wild-type mice and heterozygous transgenic mice carrying the R4496C RyR2 mutation and found that twitch force was comparable under baseline conditions (30°C, 2 mM [Ca²⁺]_o, 1 Hz). However, the positive inotropic responses to high stimulation frequency, 0.1 µM isoproterenol, and 5 mM [Ca²⁺]_o were decreased in R4496C trabeculae, as was post-rest potentiation. We investigated the mechanisms underlying inotropic insufficiency in R4496C muscles in single ventricular myocytes. Under baseline conditions, the amplitude of the Ca²⁺ transient was normal, despite the reduced SR Ca²⁺ content. Under inotropic challenge, however, R4496C myocytes were unable to boost the amplitude of Ca²⁺ transients because they are incapable of properly increasing the amount of Ca²⁺ stored in the SR because of a larger SR Ca²⁺ leakage. Recovery of force in response to premature stimuli was faster in R4496C myocardium, despite the unchanged rates of recovery of L-type Ca²⁺ channel current (I_Ca-L) and SR Ca²⁺ content in single myocytes. A faster recovery from inactivation of the mutant R4496C channels could explain this behavior. In conclusion, changes in RyR2 channel gating associated with the R4496C mutation could be directly responsible for the alterations in both ventricular and atrial contractility. The increased RyR2 P_o and fractional Ca²⁺ release from the SR induced by the R4496C mutation preserves baseline contractility despite a slight decrease in SR Ca²⁺ content, but cannot compensate for the inability to increase SR Ca²⁺ content during inotropic challenge.