Short-term responses to salinity of an invasive cordgrass

Salinity is one of the main chemical factors in salt marshes. Studies focused on the analysis of salinity tolerance of salt marsh plants are very important, since they may help to relate their physiological tolerances with distribution limits in the field. Spartina densiflora is a South America cordgrass, which has started its invasion of the European coastline from the southwestern Iberian Peninsula. In this work, short-term responses in adult tussocks of S. densiflora from southwestern Spain are studied over a wide range of salinity in a greenhouse experiment. Our results point out that S. densiflora has a high tolerance to salinity, showing high growth and net photosynthesis rates from 0.5 to 20 ppt. S. densiflora showed at the lowest salinity (0.5 ppt) high levels of photoinhibition, compensated by higher levels of energy transmission between photosystems. Adaptative mechanisms, as those described previously, would allow it to live in fresh water environments. At the highest salinity (40 ppt), S. densiflora showed a high stress level, reflected in significant decreases in growth, net photosynthesis rate and photochemical efficiency of Photosystem II. These responses support S. densiflora invasion patterns in European estuaries, with low expansion rates along the coastline and faster colonization of brackish marshes and river banks. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biodegradation of the herbicide diuron by streptomycetes isolated from soil

The diuron degrading activity of 17 streptomycete strains, obtained from agricultural and non-agricultural soils, was determined in the laboratory. All strains were identified as Streptomyces sp. by phenotypic characteristics and PCR-based assays. The strains were cultivated in liquid medium with diuron (4 mg L⁻¹) at 25 °C for 15 days. Biodegradation activity was determined by high-performance liquid chromatography. The results indicated that all strains were able to degrade diuron, but to different amounts. Twelve strains degraded the herbicide by up to 50% and four of them by up to 70%. Strain A7-9, belonging to S. albidoflavus cluster, was the most efficient organism in the degradation of diuron, achieving 95% degradation after five days of incubation and no herbicide remained after 10 days. Overall, the strains isolated from agricultural soils exhibited higher degradation percentages and rates than those isolated from non-agricultural soils. Given the high degradation activity observed here, the streptomycete strains show a good potential for bioremediation of soils contaminated with diuron.     

The design, synthesis, and evaluation of two universal doxorubicin-linkers: preparation of conjugates that retain topoisomerase II activity

The design, synthesis, and evaluation of two N-alkylmaleimide aldehydes have been achieved, which upon reductive alkylation with the C3'-amino group of doxorubicin (DOX) permits the preparation of DOX conjugates via Michael addition of thiol-containing vectors. This method enables the mild, facile, and high-throughput preparation of DOX conjugates that retain the basic C3'-nitrogen, a pre-requisite for topoisomerase II inhibition. Seven DOX-amino acid conjugates were prepared, each displaying similar inhibitory activity as the parent drug.     

Sociosexual behavior, male mating tactics, and the reproductive cycle of giraffe Giraffa camelopardalis

Female distribution exerts a major impact on male mating tactics. Giraffe cows have a reproductive cycle, and a social system, that should favor a male roaming reproductive tactic. We conducted a 2-year study of female Rothschild's giraffe (G. c. rothschildi) reproductive endocrinology in order to characterize attributes of the reproductive cycle and investigate how female endocrine and behavioral cues influence mating activity. We used non-invasive fecal steroid methods to determine reproductive state among females residing in a herd in a large outdoor enclosure. We found that females had an estrous cycle of 14.7 days and that they regularly had multiple ovarian cycles prior to conception. Adult males were more likely to associate with, and sexually investigate, females when they were cycling than when they were either pregnant or acyclic. During the estrous cycle, male-female proximity and sociosexual behavior were more pronounced during the probable fertile phase than the rest of the cycle. Sexual activity between giraffe coincided with the periovulatory period, with male interest in females peaking during the fertile window in the absence of proceptive behavior by females. We conclude that males detect reliable cues revealing female reproductive status and partition their reproductive effort in response to such cues. We propose that male giraffe adopt a roaming reproductive strategy with their large size, enabling them to search for and mate guard fertile females while minimizing metabolic costs.     

Interactions Between Nitrate Assimilation and 2,4-Dinitrophenol Cometabolism in Rhodobacter capsulatus E1F1

The phototrophic, nitrate-photoassimilating bacterium Rhodobacter capsulatus E1F1 cometabolizes 2,4-dinitrophenol (DNP) by photoreducing it to 2-amino-4-nitrophenol under anaerobic conditions. DNP uptake and nitrate metabolism share some biochemical features, and in this article we show that both processes are influenced by each other. Thus, as was demonstrated for nitrate assimilation, DNP uptake requires a thermolabile periplasmic component. Nitrate assimilation is inhibited by DNP, which probably affects the nitrite reduction step because neither nitrate reductase activity nor the transport of nitrate or nitrite is inhibited. On the other hand, DNP uptake is competitively inhibited by nitrate, probably at the transport level, because the nitroreductase activity is not inhibited in vitro by nitrate, nitrite, or ammonium. In addition, the decrease in the intracellular DNP concentration in the presence of nitrate probably inactivates the nitroreductase. These results allow prediction of a negative environmental effect if nitrate and DNP are released together to natural habitats, because it may lead to a lower rate of DNP metabolism and to nitrite accumulation.     

Effects of estradiol on phenylephrine contractility associated with intracellular calcium release in rat aorta

The ability of estradiol to affect phenylephrine-induced contraction and the subsequent increase in resting tone, associated with capacitative Ca²⁺ entry across the plasma membrane, was evaluated in rat aortic rings incubated in Ca²⁺-free solution. The incubation with estradiol (1–100 nM, 5 min) inhibited both the phenylephrine-induced contraction and the IRT. Neither cycloheximide (1 µM; inhibitor of protein synthesis) nor tamoxifen (1 µM; blocker of estrogenic receptors) modified the effects of estradiol. Estradiol (100 µM) also blocked the contractile response to serotonin (10 µM) but not to caffeine (10 mM). In addition, estradiol (100 µM) inhibited the contractile responses to cyclopiazonic acid (1 µM; selective Ca²⁺-ATPase inhibitor) associated with capacitative Ca²⁺ influx through non-L-type Ca²⁺ channels. Finally, estradiol inhibited the Ca²⁺-induced increases in intracellular free Ca²⁺ (after pretreatment with phenylephrine) in cultured rat aorta smooth muscle cells incubated in Ca²⁺-free solution. In conclusion, estradiol interfered in a concentration-dependent manner with Ca²⁺-dependent contractile effects mediated by the stimuli of ₁-adrenergic and serotonergic receptors and inhibited the capacitative Ca²⁺ influx through both L-type and non-L-type Ca²⁺ channels. Such effects are in essence nongenomic and not mediated by the intracellular estrogenic receptor. estrogen; ₁-adrenergic agonists     

Cellular immune responses associated with occult hepatitis C virus infection of the liver

Occult hepatitis C virus (HCV) infection is a type of recently identified chronic infection that is evidenced only by detection of HCV RNA in liver; patients consistently test negative for antibodies to HCV and HCV RNA in serum. Using ex vivo and in vitro measures of T-cell responses, we have identified functional virus-specific memory CD4(+) and CD8(+) T cells in the peripheral blood of patients with occult HCV infection. The features of the virus-specific T cells were consistent with immune surveillance functions, supporting previous exposure to HCV. In addition, the magnitudes of CD4(+) and CD8(+) T-cell responses were in parallel and correlated inversely with the extent of liver HCV infection. The detection of HCV-specific T cells in individuals in whom HCV RNA can persist in the liver despite the absence of viremia and antibodies indicates that HCV replication is prolonged in the face of virus-specific CD4(+) and CD8(+) T-cell responses. These findings demonstrate that HCV-specific cellular immune responses are markers not only of previous exposure to and recovery from HCV but also of ongoing occult HCV infection.     

Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basin

1. We examined the influence of hydrologic seasonality on temporal variation of planktonic bacterial production (BP) in relatively undisturbed lowland rivers of the middle Orinoco basin, Venezuela. We sampled two clearwater and two blackwater rivers over 2 years for dissolved organic carbon (DOC), chlorophyll, phosphorus and bacterial abundance to determine their relationship to temporal variation in BP. 2. Dissolved organic carbon concentration was greater in blackwater (543–664 μm ) than in clearwater rivers (184–240 μm ), and was generally higher during periods of rising and high water compared with low water. Chlorophyll concentration peaked (3 μg L^?1) during the first year of study when discharge was lowest, particularly in blackwater rivers. Soluble reactive phosphorus (SRP) was very low in the study rivers (<3.8 μg L^?1) and concentration increased during low water. 3. Average BP was higher in clearwater (0.20–0.26 μg C L^?1 h^?1) than in blackwater rivers (0.14–0.17 μg C L^?1 h^?1), although mean bacterial abundance was similar among rivers (0.6–0.8 × 10⁶ cells mL^?1). 4. Periods of higher chlorophyll a concentration (low water) or flushing of terrestrial organic material (rising water) were accompanied by higher BP, while low BP was observed during the period of high water. 5. Interannual variation in BP was influenced by variations in discharge related to El Niño Southern Oscillation events. 6. Seasonal variation in BP in the study rivers and other tropical systems was relatively small compared with seasonal variation in temperate rivers and lakes. In addition to the low seasonal variation of temperature in the tropics, low overall human disturbance could result in less variation in the inputs of nutrients and carbon to the study rivers compared with more disturbed temperate systems.