Relevance of Rheological Properties of Sodium Alginate in Solution to Calcium Alginate Gel Properties

The purpose of this study is to determine whether sodium alginate solutions’ rheological parameters are meaningful relative to sodium alginate’s use in the formulation of calcium alginate gels. Calcium alginate gels were prepared from six different grades of sodium alginate (FMC Biopolymer), one of which was available in ten batches. Cylindrical gel samples were prepared from each of the gels and subjected to compression to fracture on an Instron Universal Testing Machine, equipped with a 1-kN load cell, at a cross-head speed of 120 mm/min. Among the grades with similar % G, (grades 1, 3, and 4), there is a significant correlation between deformation work (L _E) and apparent viscosity (η _app). However, the results for the partial correlation analysis for all six grades of sodium alginate show that L _E is significantly correlated with % G, but not with the rheological properties of the sodium alginate solutions. Studies of the ten batches of one grade of sodium alginate show that η _app of their solutions did not correlate with L _E while tan δ was significantly, but minimally, correlated to L _E. These results suggest that other factors—polydispersity and the randomness of guluronic acid sequencing—are likely to influence the mechanical properties of the resultant gels. In summary, the rheological properties of solutions for different grades of sodium alginate are not indicative of the resultant gel properties. Inter-batch differences in the rheological behavior for one specific grade of sodium alginate were insufficient to predict the corresponding calcium alginate gel’s mechanical properties.     

Differential performance of marubakaido apple rootstock shoots grown in culture media containing different agar brands: dynamic rheological analysis

Shoots of the marubakaido apple rootstock grown in culture medium containing BBL agar presented significantly lower multiplication rate (MR) compared to MRs found for shoots grown in medium containing A-7002, A-7921, Select, and Phytagar as gelling agents. In addition, significant hyperhydricity was found for shoots grown in Phytagar and A-7921 agar-containing media. Analysis of elastic (G′) and viscous (G″) modulus showed that for all of the five agar brands used in this study, G′ was always much higher, i.e., typically one order of magnitude higher than G″, which characterizes a strong gel. G′ changed randomly with time for all of the agar brands studied, except for BBL, which presented progressive decline in G′ throughout the culture cycle. Examination of G′, within the same week, showed that Select agar always had the smallest G′, while Phytagar always had the highest G′. Analysis of the loss tangent (tan δ = G″/G′), a better indicator for gel behavior compared to G′ isolated, showed that tan δ for Select and Phytagar were always between tan δ values found for A-7002 and BBL. In addition, analysis of tan δ also indicated that BBL and Select agars showed a significantly weaker gel network, compared to Phytagar, A-7002 and A-7921 agars after the third week of culture. When seen together, these results indicate that shoot performance for the marubakaido rootstock is not related to agar gel strength. In addition, the high hyperhydricity rate found for shoots grown on agars A-7921 and Phytagar could not be related to agar gel strength, as well. Analysis of HPSEC profiles indicated that the best performance, i.e., multiplication rate, of marubakaido shoots in agars A-7002 and A-7921 is likely to be related to their lower polydispersity and/or smaller amount of high molecular weight fractions, compared to BBL, Phytagar, and Select agars.     

Nanocarrier for the Transdermal Delivery of an Antiparkinsonian Drug

The purpose of the present study was to investigate the potential of nanoemulsions as nanodrug carrier systems for the percutaneous delivery of ropinirole. Nanoemulsions comprised Capryol 90 as the oil phase, Tween 20 as the surfactant, Carbitol as the cosurfactant, and water as an external phase. The effects of composition of nanoemulsion, including the ratio of surfactant and cosurfactant (S _mix) and their concentration on skin permeation, were evaluated. All the prepared nanoemulsions showed a significant increase in permeation parameters such as steady state flux (J _ss) and permeability coefficient (K _p) when compared to the control (p < 0.01). Nanoemulsion composition (NEL3) comprising ropinirole (0.5% w/w), Capryol 90 (5% w/w), S _mix 2:1 (35% w/w), and water (59.5% w/w) showed the highest flux (51.81 ± 5.03 μg/cm²/h) and was selected for formulation into nanoemulsion gel. The gel was further optimized with respect to oil concentration (Capryol 90), polymer concentration (Carbopol), and drug content by employing the Box–Behnken design, which statistically evaluated the effects of these components on ropinirole permeation. Oil and polymer concentrations were found to have a negative influence on permeation, while the drug content had a positive effect. Nanoemulsion gel showed a 7.5-fold increase in skin permeation rate when compared to the conventional hydrogel. In conclusion, the results of the present investigation suggested a promising role of nanoemulsions in enhancing the transdermal permeation of ropinirole.     

Temporal Aroma Release Profile of Solid and Liquid Droplet Emulsions

The release kinetics of four model aroma compounds from coarse (d ₃₂ = 1.0 μm) and fine (d ₃₂ = 0.25 μm) eicosane and hydrogenated palm stearin (HPS) emulsions prepared with either solid or liquid lipid droplets were measured using a model mouth instrument. For both lipids, the release of aroma compounds from emulsions with solid droplets was higher than from emulsions with liquid droplets. This difference was greater for less polar aroma compounds. The release from solid eicosane droplets increased with particle size but no such effect was observed for HPS emulsions, however, the release from solid eicosane was higher than solid HPS. The initial aroma release profile of the solid droplet emulsion matches that of a similar liquid oil emulsion but requires much less added aroma. Meeting presentation: Presented at 98th AOCS Annual Meeting and Expo in Quebec City, Canada.     

Influence of stand structure on carbon-13 of vegetation, soils, and canopy air within deciduous and evergreen forests in Utah, United States

Carbon isotope ratios (δ¹³C) were studied in evergreen and deciduous forest ecosystems in semi-arid Utah (Pinus contorta, Populus tremuloides, Acer negundo and Acer grandidentatum). Measurements were taken in four to five stands of each forest ecosystem differing in overstory leaf area index (LAI) during two consecutive growing seasons. The δ¹³C_leaf (and carbon isotope discrimination) of understory vegetation in the evergreen stands (LAI 1.5–2.2) did not differ among canopies with increasing LAI, whereas understory in the deciduous stands (LAI 1.5–4.5) exhibited strongly decreasing δ¹³C_leaf values (increasing carbon isotope discrimination) with increasing LAI. The δ¹³C values of needles and leaves at the top of the canopy were relatively constant over the entire LAI range, indicating no change in intrinsic water-use efficiency with overstory LAI. In all canopies, δ¹³C_leaf decreased with decreasing height above the forest floor, primarily due to physiological changes affecting c _i/c _a (> 60%) and to a minor extent due to δ¹³C of canopy air (< 40%). This intra-canopy depletion of δ¹³C_leaf was lowest in the open stand (1‰) and greatest in the denser stands (4.5‰). Although overstory δ¹³C_leaf did not change with canopy LAI, δ¹³C of soil organic carbon increased with increasing LAI in Pinus contorta and Populus tremuloides ecosystems. In addition, δ¹³C of decomposing organic carbon became increasingly enriched over time (by 1.7–2.9‰) for all deciduous and evergreen dry temperate forests. The δ¹³C_canopy of CO₂ in canopy air varied temporally and spatially in all forest stands. Vertical canopy gradients of δ¹³C_canopy, and [CO₂]_canopy were larger in the deciduous Populus tremuloides than in the evergreen Pinu contorta stands of similar LAI. In a very wet and cool year, ecosystem discrimination (Δ_e) was similar for both deciduous Populus tremulodies (18.0 ± 0.7‰) and evergreen Pinus contorta (18.3 ± 0.9‰) stands. Gradients of δ¹³C_canopy and [CO₂]_canopy were larger in denser Acer spp. stands than those in the open stand. However, ¹³C enrichment above and photosynthetic draw-down of [CO₂]_canopy below tropospheric baseline values were larger in the open than in the dense stands, due to the presence of a vigorous understory vegetation. Seasonal patterns of the relationship δ¹³C_canopy versus 1/[CO₂]_canopy were strongly influenced by precipitation and air temperature during the growing season. Estimates of Δ_e for Acer spp. did not show a significant effect of stand structure, and averaged 16.8 ± 0.5‰ in 1933 and 17.4 ± 0.7‰ in 1994. However, Δ_e varied seasonally with small fluctuations for the open stand (2‰), but more pronounced changes for the dense stand (5‰). Received: 15 April 1996 / Accepted: 19 October 1996     

Influence of water activity and temperature on in vitro growth of surface cultures of a Phoma sp. and production of the pharmaceutical metabolites, squalestatins S1 and S2

A Phoma sp., known to produce the pharmaceutically active metabolites squalestatin 1 (S1) and squalestatin 2 (S2), was cultured on malt-extract/agar (MEA) over a range of water activities (a _w, 0.995–0.90) and temperatures (10–35 °C) to investigate the influence on growth and metabolite production. Use of the ionic solute NaCl to adjust a _w resulted in significantly lower (P < 0.01) squalestatin yields than when the Phoma sp. was grown on MEA amended with the non-ionic solute glycerol. Water activity and temperature and their interactions were highly significant factors (P < 0.001) affecting growth of the Phoma sp., with optimum conditions of 0.998–0.980 a _w and 25 °C. Squalestatin production was similarly influenced by a _w, temperature, time and their interactions (P < 0.001). S1 and S2 production occurred over a narrower a _w and temperature range than growth, with a slightly lower optimum a _w range of 0.995–0.980 a _w. The optimum temperature for squalestatin production varied from 20 °C (S1) to 25 °C (S2) and yields of S2 were up to 1000 times lower than those of S1. The ratio of S1 and S2 produced by the Phoma sp. was influenced by a _w and temperature, with highest values at 0.99–0.98 a _w, and at 15 °C. Incubation times of 28 days gave highest yields of both S1 and S2. Up to 2000-fold increases in squalestatin yields were measured at optimum environmental conditions, compared to the unmodified MEA. This indicates the need to consider such factors in screening systems used to detect biologically active lead compounds produced by fungi. Received: 2 June 1997 / Received last revision: 6 November 1997 / Accepted: 7 November 1997     

Characterization and Stability of Emulsion Gels Based on Acrylamide/Sodium Acryloyldimethyl Taurate Copolymer

Sepineo P 600, a concentrated dispersion of acrylamide/sodium acryloyldimethyl taurate copolymer in isohexadecane, has self-gelling and thickening properties and the ability to emulsify oily phases, which make it easy to use in the formulation of gels and o/w emulsion gels. In this paper, gels were prepared using a Sepineo P 600 concentration between the 0.5% and 5% (w/w), and then emulsion gel was also prepared from the 3% Sepineo gel by adding a specific amount of almond oil. All the prepared systems were analyzed and characterized by oscillation rheology and acoustic spectroscopy. The particle size of the oil droplets and the microrheological extensional moduli (G′ and G″) of the systems were determined from acoustic parameters and used together with the classical oscillatory rheological tests to assess the stability of the systems. Classical oscillatory analysis revealed that the dynamic moduli were very dependent on polymer concentration; as this parameter increased, there was progressive improvement in the sample elasticity. In fact, the mechanical spectra of the 0.5% and 1% (w/w) Sepineo samples were characterized by strong frequency dependence and multiple crossover points, typical of dilute polymer solution with no organized structure. On the other hand, the 3–5% (w/w) concentration systems showed typical gel-like spectra, marked by the absence of crossover points between the dynamic moduli and by weak dependence on frequency. Nevertheless, the elastic properties of the gel-like structure even at elevated polymer concentrations were not strongly long-lasting, as demonstrated by the increase of the viscous contribution in the low frequency range during acoustic spectroscopy analysis. This fact could indicate that the gel structure is characterized by weak polymer–polymer interactions, an advantageous characteristic for topical administration, as the sample is thus easier to rub into the skin. Finally, both rheology and acoustic spectroscopy indicated that addition of the oily phase caused minimal changes to the elastic character of the gel. Thus, Sepineo P 600 gel and emulsion gel are very effective systems for use in topical and other types of applications.     

Landscape genetic structure of <Emphasis Type="Italic">Betula maximowicziana</Emphasis> in the Chichibu mountain range,central Japan

We evaluated the genetic structure of 16 Betula maximowicziana populations in the Chichibu mountain range, central Japan, located within a 25-km radius; all but two populations were at altitudes of 1,100–1,400 m. The results indicate the effects of geographic topology on the landscape genetic structure of the populations and should facilitate the development of local-scale strategies to conserve and manage them. Analyses involving 11 nuclear simple sequence repeat loci showed that most populations had similar intrapopulation genetic diversity parameters. Population differentiation (F _ST = 0.021, G′_ST = 0.033) parameters for the populations examined were low but were relatively high compared to those obtained in a previous study covering populations in a much larger area with a radius of approximately 1,000 km (F _ST = 0.062, G′_ST = 0.102). Three populations (Iriyama, Kanayamasawa, and Nishizawa) were differentiated from the other populations by Monmonier’s and spatial analysis of molecular variance algorithms or by STRUCTURE analysis. Since a high mountain ridge (nearly 2,000 m) separates the Kanayamasawa and Nishizawa populations from the other 14 populations and the Kanayamasawa and Nishizawa populations are themselves separated by another mountain ridge, the genetic structure appears to be partly due to mountain ridges acting as genetic barriers and restricting gene flow. However, the Iriyama population is genetically different but not separated by any clear geographic barrier. These results show that the landscape genetic structure is complex in the mountain range and we need to pay attention, within landscape genetic studies and conservation programs, to geographic barriers and local population differentiation.     

Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana)

Canopy CO₂ concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season and the 1995 wet season. Carbon dioxide concentrations ([CO₂]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height into the canopy. During both seasons, daytime [CO₂] in the upper and middle canopy decreased on average 7–10 μmol mol⁻¹ below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO₂] did not differ between the wet and dry seasons. In contrast, [CO₂] below 0.7 m were generally higher during the dry season, resulting in larger [CO₂] gradients. Supporting this observation, soil CO₂ efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events, resulting in a rapid decrease in canopy [CO₂] immediately above the forest floor of about 50␣μmol mol⁻¹. Temporal and spatial variations in [CO₂]_canopy were reflected in changes of δ¹³C_canopy and δ¹⁸O_canopy values. Tight relationships were observed between δ¹³C and δ¹⁸O of canopy CO₂ during both seasons (r ² > 0.86). The most depleted δ¹³C_canopy and δ¹⁸O_canopy values were measured immediately above the forest floor (δ¹³C = −16.4‰; δ¹⁸O = 39.1‰ SMOW). Gradients in the isotope ratios of CO₂ between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ¹³C, and between 1.0‰ and 3.5‰ for δ¹⁸O. The δ¹³C_leaf and calculated c _i/c _a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ¹³C_leaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c _i/c _a. Plotting 1/[CO₂] vs. the corresponding δ¹³C ratios resulted in very tight, linear relationships (r ² = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ¹³C of respired sources were close to the measured δ¹³C of soil respired CO₂ and to the δ¹³C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δ_e, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season. Received: 3 March 1996 / Accepted: 19 October 1996     

Molecular cloning, expression, and purification of pig interleukin-5

 Interleukin-5 (IL-5) is thought to be a key cytokine in allergic inflammation. Pig IL-5 was cloned, sequenced, and expressed to enable us to study of the biological role of IL-5 in pigs used in a model for allergen-induced late-phase reactions. These pigs were sensitized to proteins extracted from Ascaris suum, resulting in hypersensitivity to this antigen in both the skin and airways, and a slight blood eosinophilia. Peripheral blood mononuclear cells from antigen-sensitized pigs were isolated and polyclonally stimulated. Total RNA was extracted and reverse transcribed into cDNA. IL-5 primers based on the cow IL-5 cDNA sequence were used to obtain an initial polymerase chain reaction product. 3′ rapid amplification of cDNA ends (3′RACE) and 5′RACE procedures were applied to identify the 3′ and 5′ ends, respectively. The full-length pig IL-5 cDNA is 405 base pairs long. Mature pig IL-5 was expressed in Escherichia coli with a His-tag for purification. The IL-5 protein is 115 amino acids long, has an estimated molecular weight of 14 000 M _r and forms a biologically active homodimer of 28 000 M _r . Pig IL-5 shows 65% amino acid identity to the human IL-5 sequence and 90, 88, 83, 62, and 61% identity to the cow, sheep, horse, mouse, and rat counterparts. Received: 29 June 1999 / Revised: 22 September 1999     

Effects of Pulsed Electric Field on the Viscoelastic Properties of Potato Tissue

We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths (E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10⁻⁵, 10⁻⁴, or 10⁻³ s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through small amplitude oscillatory dynamic rheological measurements. The elastic (G′) and viscous moduli (G″) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-δ) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Results show a drastic increase of tan-δ in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-δ to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-δ after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application.     

Pulse waves for a semi-discrete Morris–Lecar type model

 We establish the existence of a pulse traveling wave for an infinite system of ODEs modeling a one dimensional string of nerve cells of identical Morris–Lecar type dynamics:

Interfacial and Emulsifying Characteristics of Acid-treated Pea Protein

This work presents equilibrium and dynamic aspects for the adsorption at the oil–water interface of pea (Pisum sativum L.) protein isolate (PPI). Dynamic interfacial tension, γ, and surface viscoelasticity modulus, ε, were determined using pendant-drop method. Adsorption kinetics studies revealed that pea proteins adsorb faster at pH 7.0 than at acidic pH (pH 2.4). On the other hand, the measured ε is lower at pH 7.0. This is probably due to fast adsorption, leading to the formation of inhomogeneous film structures. In fact, compared with pHs above the isoelectric point (pI ~ 4.3), acidic conditions slow down the adsorption, but the modulus is increased. Pea-protein-stabilized emulsions are more stable to creaming at acidic pH and their particle-size distributions are more homogeneous in these conditions. Effect of pH on interfacial properties and on properties of oil-in-water emulsions stabilized by PPI was interpreted in terms of pea protein solubility, globulin dissociation, and oil-droplet surface electrostatic charge. We propose that at acidic conditions, adsorbed dissociated globulins form stronger and denser viscoelastic networks when adsorbed at oil–water interface. Consequently, the pH-dependence of pea-globulin-stabilized emulsions properties could be of great interest to tune barrier properties of oil/water interfacial membranes for several applications such as encapsulation and controlled release of lipophilic bioactive components within the food, medical, and pharmaceutical industries.     

Effect of Polyglycerol Esters of Fatty Acids on the Physicochemical Properties and Stability of β-Carotene Emulsions during Digestion in Simulated Gastric Fluid

The effects of six different polyglycerol esters of fatty acids (PGEs) and two different particle sizes produced using various processing parameters on the physicochemical properties and stability of the β-carotene emulsions during digestion in simulated gastric fluid (SGF) were investigated. β-Carotene emulsions were prepared by high-pressure homogenization using β-carotene (0.1% w/w) in soybean oil as the oil phase and 1% (w/w) PGE in Milli-Q water as the water phase. The particle size of β-carotene emulsions was measured by a laser diffraction technique, and the stability of emulsions was interpreted in terms of the increase in particle size and span value of emulsion droplets and the retention of β-carotene during digestion in SGF. The average particle size ranges of emulsions were 0.17 to 0.27 μm for fine emulsions and 1.16 to 1.59 μm for coarse emulsions. In the prepared β-carotene emulsions, the particle size decreased with increasing polymerization of the glycerol in PGEs, and the higher polymerization of the glycerol also increased the stability of emulsions during digestion in SGF. Although the β-carotene content in the emulsions significantly decreased with increasing digestion period, loss of β-carotene was more severe in unstable emulsions than in stable emulsions, suggesting that the particles incorporated into droplets could provide some protective barrier for decreasing the β-carotene degradation. Therefore, β-carotene emulsions stabilized by PGEs with high polymerization of the glycerol may be useful for further applications in food and drug formulations. Decaglycerol monooleate (MO750) was demonstrated to be the most effective emulsifier in stabilizing β-carotene emulsions in this study.     

Transdermal Delivery of an Anti-Cancer Drug via W/O Emulsions Based on Alkyl Polyglycosides and Lecithin: Design,Characterization, and <Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of the Possible Irritation Potential in Rats

The purpose of this work was to develop w/o emulsions that could be safely used to promote transdermal delivery of 5-fluorouracil (5-FU). Two pseudo-ternary phase diagrams comprising oleoyl-macrogol glycerides, water, and a surfactant/co-surfactant (S/CoS) mixture of lecithin, ethanol, and either coco glucoside or decyl glucoside were investigated for their potential to develop promising 5-FU emulsions. Six systems were selected and subjected to thermodynamic stability tests; heat–cool cycles, centrifugation, and finally freeze–thaw cycles. All systems passed the challenges and were characterized for transmission electron microscopy, droplet size, rheological behavior, pH, and transdermal permeation through newly born mice skin in Franz diffusion cells. The systems had spherical droplets ranging in diameter from 1.81 to 2.97 μm, pH values ranging from 7.50 to 8.49 and possessed Newtonian flow. A significant (P < 0.05) increase in 5-FU permeability parameters as steady-state flux, permeability coefficient was achieved with formula B5 comprising water (5% w/w), S/CoS mixture of lecithin/ethanol/decyl glucoside (14.67:12.15:18.18% w/w, respectively) and oleoyl-macrogol glycerides (50% w/w). When applied to shaved rat skin, this system was well tolerated with only moderate skin irritation that was recovered within 12 h. Indeed, minor histopathologic changes were observed after 5-day treatment. Further studies should be carried out, in the future, to investigate the potentiality of this promising system to promote transdermal delivery of 5-FU through human skin.     

Contributions of C3 and C4 plants to higher trophic levels in an Amazonian savanna

We studied the energy flow from C₃ and C₄ plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C₄ plants encountered in our study area were grasses and all C₃ plants were bushes, shrubs or vines. Differences in δ¹³C ratios among bushes (xˉ = −30.8, SD = 1.2), vines (xˉ = −30.7, SD = 0.46) and trees (xˉ = −29.7, SD = 1.5) were small. However the mean δ¹³C ratio of dicotyledonous plants (xˉ = −30.4, SD = 1.3) was much more negative than that of the most common grasses (xˉ = −13.4, SD = 0.27). The insect primary consumers had δ¹³C ratios which ranged from a mean of −29.5 (SD = 0.47) for the grasshopper Tropidacris collaris to a mean of −14.7 (SD = 0.56) for a termite (Nasutitermes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for δ¹³C, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher values of δ¹³C (xˉ = −21.7, SD = 1.6; xˉ = −21.9, SD = 1.8, respectively) than the birds (xˉ = −24.8, SD = 1.8) and the only species of mammal resident in the savanna (xˉ = −25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C₄ grasses. Received: 7 May 1998 / Accepted: 30 November 1998     

Individual and Joint Toxicity Effects of Cu,Cr(III), and Cr(VI) on Pakchoi: A Comparison Between Solution and Soil Cultures

The single and joint toxicity effects of Cu, Cr(III), and Cr(VI) on the root elongation of pakchoi in solution and soil were investigated. The median effective concentration (EC₅₀) was determined to examine the toxic thresholds of the test elements. The results showed that individual contamination by Cu, Cr(III), or Cr(VI) can inhibit the root elongation of pakchoi. The EC₅₀ values of the test elements were 2.02 mg/L and 195.8 mg/kg, 62.2 mg/L and 1,773 mg/kg, and 6.88 mg/L and 8.08 mg/kg in solution and soil, respectively. Toxic unit (TU) was introduced to determine the outcome in combined tests, and different behaviors were observed in both solution and soil. The coexistence of Cu and Cr(III) in solution exhibited an antagonistic effect (EC_50mix = 1.76 TU_mix), whereas a synergistic effect was observed in soil (EC_50mix = 0.76 TU_mix). In contrast, combined Cu–Cr(VI) showed a less than additive toxicity both in solution and soil, with EC_50mix values of 3.31 and 1.24 TU_mix. In conclusion, the coexistence of toxicity in Cu–Cr(III) and Cu–Cr(VI) differs from the toxicity exhibited individually by Cu, Cr(III), and Cr(VI). Heavy metal interaction also changes depending on the medium.     

Influences of different nitrogen sources on nitrogen- and water-use efficiency, and carbon isotope discrimination, in C3 Triticum aestivum L. and C4 Zea mays L. plants

The impacts of various nitrogen sources, i.e. NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ in combination with gaseous NH₃, on nitrogen-, carbon- and water-use efficiency and ¹³C discrimination (δ¹³C) by plants of the C₃ species Triticum aestivum L. (wheat) and the C₄ species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m⁻³ of N supplied as NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ for 21 and 18 d, respectively, and thereafter exposed to gaseous NH₃ at 320 μg · m⁻³ or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH₄NO₃-N > NO⁻ ₃-N > NH₄ ⁺-N and NO⁻ ₃-N > NH₄NO₃-N > NH₄ ⁺-N, respectively. Fumigation with NH₃ decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH₄ ⁺-N > NO⁻ ₃-N≈NH₄NO₃-N in non-fumigated T. aestivum, while fumigation with NH₃ increased the WUE of NO⁻ ₃-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ¹³C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH₄ ⁺-grown plants of T. aestivum and Z. mays than in those supplied with NH₄NO₃ or NO⁻ ₃. Regardless of the N-form supplied to the roots of the plant species, exposure to NH₃ caused more-positive δ¹³C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ¹³C values in plants of T. aestivum and Z. mays. These differences in δ¹³C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source. Received: 12 September 1997 / Accepted: 13 January 1998     

Structural and Mechanical Behavior of Tristearin/Triolein-rich Mixtures and the Modification Achieved by Interesterification

The effects of chemical and enzymatic interesterification on the structure and rheological behavior of blends of fully hydrogenated canola oil (FHCO) with high oleic acid sunflower oil in the range of 10–90% was studied. Relationships between chemical composition, crystallization temperature (20–50°C), solid fat content (SFC) of the blends, and their rheological properties, characterized using both small and large deformation mechanical testing, were investigated. The storage modulus (G′) and yield force increased with FHCO concentration in the blends and was affected strongly by interesterification. The SFC in the interesterified samples was lower than in the non-interesterified blends, but they had higher values of G′. This increase in G′ at 30°C upon interesterification was attributed to a decrease in the fractal dimension of the fat crystal network which translates into a decrease in crystal cluster size in the interesterified samples. The higher G′ in the chemically interesterified samples relative to the enzymatic interesterified samples, on the other hand, was due to a higher λ parameter which is directly proportional to the strength of interparticle interactions and inversely proportional to crystal size. Microscopy and nucleation kinetics studies allowed for the independent determination of λ.