Evaluation of biocompatibility and mechanical behavior of chitin-based polyurethane elastomers. Part-II: Effect of diisocyanate structure

Chitin-based polyurethane elastomers having potential for biomedical applications with tunable mechanical properties were synthesized by step growth polymerization techniques using poly(?-caprolactone) (PCL) with different diisocyanates. The prepolymer was extended using chitin and/or 1,4-butane diol (BDO). The structures of the resulted polymers were determined by Fourier transform infrared (FTIR), ¹H NMR and ¹³C NMR spectroscopic techniques. The effect of structure of diisocyanates and chain extenders on mechanical properties and in vitro biocompatibility were investigated. The results revealed that the final polymers extended with chitin are preferred candidates for surgical threads with on going investigations into their in vitro biocompatibility and non-toxicity.     

Shoot regeneration and free-radical scavenging activity in <Emphasis Type="Italic">Silybum marianum</Emphasis> L.

The morphogenic potential and free-radical scavenging activity of the medicinal plant, Silybum marianum L. (milk thistle) were investigated. Callus development and shoot organogenesis were induced from leaf explants of wild-grown plants incubated on media supplemented with different plant growth regulators (PGRs). The highest frequency of callus induction was observed on explants incubated on Murashige and Skoog (MS) medium supplemented with 5.0 mg l⁻¹ 6-benzyladenine (BA) after 20 days of culture. Subsequent transfer of callogenic explants onto MS medium supplemented with 2.0 mg l⁻¹ gibberellic acid (GA₃) and 1.0 mg l⁻¹ α-naphthaleneacetic acid (NAA) resulted in 25.5 ± 2.0 shoots per culture flask after 30 days following culture. Moreover, when shoots were transferred to an elongation medium, the longest shoots were observed on MS medium supplemented with 0.5 mg l⁻¹ BA and 1.0 mg l⁻¹ NAA, and these shoots were rooted on a PGR-free MS basal medium. Assay of antioxidant activity of in vitro and in vivo grown tissues revealed that significantly higher antioxidant activity was observed in callus than all other regenerated tissues and wild-grown plants.     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

Effect of divalent metal ions on soluble and membrane-bound alkaline phosphatase activity in suckling rat intestine.

EDTA treatment of intestinal brush border membranes (BBM) and epithelial cell supernatant completely inhibited alkaline phosphatase (AP) activity in suckling rat intestine. AP activity was fully regained upon dialysis of the preparations against Zn2+ and to a lesser extent against Co2+, Ca2+ and Mn2+ ions. Other metal ions (Cd2+ and Mg2+) tested were essentially ineffective in restoring the enzyme activity. Considerable differences were observed in kinetic characteristics of the membrane-bound and soluble AP activities in response to various metal ions. There were apparent differences in Km, Vmax, energy of activation (Ea) and thermal stability of the soluble and membrane-bound AP activities, after metal ion substitutions. Nearly 35% AP activity was solubilized on sodium dodecyl sulphate treatment of brush borders (membrane protein: detergent ratio 1:3; w/w). Dialysis of detergent solubilized BBM against different metal ions reconstituted AP activity in the particulate fraction: the order of effectiveness was Zn greater than Ca greater than Mn greater than Co. The kinetic properties of the reconstituted AP were essentially similar to the non-integrated enzyme activity in response to various divalent metal ions examined. But there were apparent differences in Km, Vmax, Ea and thermal stability of the reconstituted AP activity compared to native brush border enzyme. The results suggest the unique requirement of Zn ions for stability and catalytic activity of the soluble and membrane-bound AP activity in suckling rat intestine.     

Error in assay due to time dependency of carbon monoxide difference spectrum of reduced yeast cytochrome P-450: Slow reduction caused by Triton X-100 present

Triton X-100, added to yeast Saccharomyces cerevisiae for the purpose of stabilization or solubilization affects the carbon monoxide difference spectrum of reduced cytochrome P-450 and consequently the measurement of cytochrome P-450. Eight minutes is needed for 450-nm peak to reach its maximum height. Triton X-100 is shown to behave as a Type II substrate (absorption maximum at 418 nm and minimum at 390 nm) and to modulate the spin state of cytochrome P-450 from high to low form. Low-spin yeast cytochrome P-450 is reduced more slowly than the high-spin form.     

Hydrology Affects Environmental and Spatial Structuring of Microalgal Metacommunities in Tropical Pacific Coast Wetlands

The alternating climate between wet and dry periods has important effects on the hydrology and therefore on niche-based processes of water bodies in tropical areas. Additionally, assemblages of microorganism can show spatial patterns, in the form of a distance decay relationship due to their size or life form. We aimed to test spatial and environmental effects, modulated by a seasonal flooding climatic pattern, on the distribution of microalgae in 30 wetlands of a tropical dry forest region: the Pacific coast of Costa Rica and Nicaragua. Three surveys were conducted corresponding to the beginning, the highest peak, and the end of the hydrological year during the wet season, and species abundance and composition of planktonic and benthic microalgae was determined. Variation partitioning analysis (as explained by spatial distance or environmental factors) was applied to each seasonal dataset by means of partial redundancy analysis. Our results show that microalgal assemblages were structured by spatial and environmental factors depending on the hydrological period of the year. At the onset of hydroperiod and during flooding, neutral effects dominated community dynamics, but niche-based local effects resulted in more structured algal communities at the final periods of desiccating water bodies. Results suggest that climate-mediated effects on hydrology can influence the relative role of spatial and environmental factors on metacommunities of microalgae. Such variability needs to be accounted in order to describe accurately community dynamics in tropical coastal wetlands.     

Homozygous chromosomal aberrations in Anopheles stephensi

Homozygotes for six autosomal paracentric inversions, an inserted paracentric inversion, an autosomal translocation, and two X-chromosome-chromosome 3 translocations in Anopheles stephensi are described. Three of these aberrations are being maintained in pure strains without the necessity of selection.