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At least 451 records · Page 25Linked to original sources
PubMed2003

Mineral toxicity and physiological functions in tree seedlings irrigated with effluents of varying chemistry in sandy soil of dry region.

Effluents namely canal water as control (T1); municipal effluent (T2); textile effluent (T3); steel effluent (T4); textile + municipal effluent in 1:1 ratio (T5); steel + municipal effluent in 1:2 ratio (T6); steel + municipal + textile in 1:2:2 ratio (T7); and steel + textile in 1:2 ratio (T8) were added to the seedlings of Acacia nilotica and Eucalyptus camaldulensis. The aim was to monitor the toxic effect of the accumulated mineral ions on the physiological functions and ultimately to utilize these effluents in tree plantation. Foliage mineral concentration, leaf water potential (LWP), rate of photosynthesis (Pn), rate of transpiration (T) and stomatal conductance (g) were recorded. Mineral accumulation increased in the seedlings of T2 treatment. However, the accumulation of Mn, Fe, Cu and Zn was the highest (p<0.001) in the seedlings of T4, T6, T7, and T8 treatments affecting N, P, K, Ca, Mg, and Na concentration. The seedlings of T3 treatment had less Mg, Mn, Fe, Cu, and Zn and medium N, Ca, and P concentration, which were negatively correlated with Na concentration in foliage and the amount added through effluent irrigation. Concentration of N, K, Ca, Mg, and Na was higher in the foliage of A. nilotica whereas P, Mn, Fe, Cu, and Zn were high in E. camaldulensis. Early two months data showed reduction (p<0.01) in Pn (87%), T (81%), g (67%), and LWP as a result of metal stresses (toxicity) in T6, T7, and T8 seedlings. E. camaldulensis maintained high LWP and Pn and low T and g compared to A. nilotica. High LWP in the seedlings of T2 was associated (p<0.05) high Pn, T, and g. However, these physiological parameters lowered in the seedlings of T3 and T5. Seedlings of T1, T2, and T5 maintained high LWP, Pn, T, and g throughout the experimental period. These parameters however, decreased (p<0.01) in the seedlings of T3 treatment subsequently through Na induced deficiency of Mg, Ca, Mn, Fe, Cu, and Zn. The enhanced physiological functions in T5 treatment were probably the result of ameliorative effect of municipal effluent through increased mineral status. The study suggests that excess accumulation of Na, Mn, Fe, Cu, and Zn leads to metal toxicity that adversely affects physiology of the tree seedlings. Mixing of effluents and/or removal of excess would ameliorate these toxic effects and could be the better management practices for their use in tree irrigation.

Acacia↗
PubMed2006

Winning by a neck: tall giraffes avoid competing with shorter browsers.

With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.

Acacia↗
PubMed2002

Metabolomics of plant saponins: bioprospecting triterpene glycoside diversity with respect to mammalian cell targets.

One of the goals of cancer chemotherapy and prevention is the discovery of compounds that are relatively selective to tumor cells and, therefore, have reduced effects on normal cell growth. In previously published studies, it was shown that certain triterpene saponins (called avicins) from a desert tree, Acacia victoriae, are selectively toxic to tumor cells at very low doses (IC(50): 0.2 microg/mL for Jurkat cells). To extend this research to human clinical studies, we needed to find a reliable supply of avicins and have developed a transformed "hairy root" culture as a means of biomass production. Protocols were optimized for A. victoriae micropropagation; after a boiling water treatment, A. victoriae seeds were maintained under in vitro conditions on defined media. Embryo-axis explants from shoot tips were removed and infected with Agrobacterium rhizogenes Conn (R 1000) for hairy root induction. Plasmid integration was confirmed by PCR analysis with a primer set for a segment of the rol B gene. Culture conditions have been optimized for root biomass production, and various inducers have been investigated for enhancement of avicin production. Hairy root cultures were compared with intact pod tissue from field-grown sources for avicin content following partial purification of triterpene glycosides and HPLC separation of the secondary metabolites. From bioassays of the collected HPLC fractions, we have identified putative triterpene "metabolic clusters" with enhanced activity against tumor cells. This now provides a system for both production of clinical trial lots of active samples, but also a means to correlate structure of individual triterpene glycosides with specific cellular target activity in mammalian cells.

Acacia↗
PubMed2006

Inbreeding ancestors: the role of sibmating in the social evolution of gall thrips.

We used microsatellite data to estimate levels of inbreeding in four species of solitary gall thrips that are in the same clade as the six species with soldier castes. Three of the four species were highly inbred (Fis 0.54-0.68), and the other apparently mated randomly (Fis near zero). These estimates, combined with previous data from species with soldiers, suggest that inbreeding is a pervasive life-history feature of the gall-inducing thrips on Australian Acacia. Mapping of inbreeding estimates onto the phylogeny of the gall inducers showed that the ancestral lineage that gave rise to soldiers was apparently highly inbred, and therefore, inbreeding could have played a role in the origin of sociality within this group. Moreover, there was a trend from high levels of inbreeding at the origin of soldiers to low levels in the most derived species with soldiers, which exhibits the highest levels of reproductive division of labor and soldier altruism. These patterns are consistent with considerations from population genetics, which show that the likelihood of the origin of soldier altruism is higher in inbreeding populations but that, once soldiers have evolved, a reduction in inbreeding levels may facilitate the evolution of enhanced division of labor and reproductive skew.

Acacia↗
PubMed2002

Influence of natural temperature gradients on measurements of xylem sap flow with thermal dissipation probes. 1. Field observations and possible remedies.

The thermal dissipation method is simple and widely used for measuring sap flow in large stems. As with several other thermal methods, natural temperature gradients are assumed to be negligible in the sapwood being measured. We studied the magnitude and variability of natural temperature gradients in sapwood of Acacia trees growing in the Sahelian zone of Senegal, analyzed their effects on sap flow measurements, and investigated possible solutions. A new measurement approach employing cyclic heating (45 minutes of heating and 15 minutes of cooling; 45/15) was also tested. Three-day measurement sequences that included 1 day without heating, a second day with continuous heating and a third day with cyclic heating were recorded during a 6.5-month period using probes installed at three azimuths in a tree trunk. Natural temperature gradients between the two probes of the sensor unit, spaced 8 to 10 cm vertically, were rarely negligible (i.e., < 0.2 degrees C): they were positive during the night and negative during the day, with an amplitude ranging from 0.3 to 3.5 degrees C depending on trunk azimuth, day and season. These temperature gradients had a direct influence on the signal from the continuously heated sensors, inducing fluctuations in the nighttime reference signal. The resulting errors in sap flow estimates can be greater than 100%. Correction protocols have been proposed in previous studies, but they were unsuitable because of the high spatial and temporal variability of the natural temperature gradients. We found that a measurement signal derived from a noncontinuous heating system could be an attractive solution because it appears to be independent of natural temperature gradients. The magnitude and variability of temperature gradients that we observed were likely exacerbated by the combination of open stand, high solar radiation and low sap flow rate. However, for all applications of the thermal dissipation method, it is wise to check regularly for natural temperature gradients by switching off the heater.

Acacia↗
PubMed2004

Photosynthesis, carbohydrate storage and survival of a native and an introduced tree species in relation to light and defoliation.

Fraxinus uhdei (Wenz.) Lingelsh (tropical ash), a species introduced to Hawaii from Mexico, invades forests of the endemic tree Acacia koa A.Gray (koa). We examined physiological and morphological characteristics of koa and tropical ash to explore possible mechanisms that may facilitate invasion of koa forests by tropical ash. Seedlings of both species were grown in a greenhouse in three light treatments: 100% photosynthetic photon flux (PPF); 18% PPF; and 2% PPF inside the greenhouse. Light compensation point, maximum CO2 assimilation rate and dark respiration rate of seedlings differed significantly among light treatments, but were similar between species. A defoliation experiment indicated that tropical ash was better able to survive defoliation than koa, especially under high-light conditions. Tropical ash seedlings allocated more carbon (C) and nitrogen (N) to storage per unit PPF than koa seedlings. Total nonstructural carbohydrates were positively correlated with plant survival in both species. The patterns of C and N allocation associated with tropical ash seedlings favor their survival in high light, under intense herbivory and on sites where N availability is seasonal or highly variable. Variation in carbohydrate storage between koa and tropical ash greatly exceeded variation in photosynthetic performance at the leaf level.

Acacia↗
PubMed2006

Interspecific variation in vessel size, growth and drought tolerance of broad-leaved trees in semi-arid regions of Kenya.

In semi-arid regions, trees often wither during the dry season. Withering is sometimes manifest as die-back, whereby whithering results in shoot death, which progresses downward from the uppermost part of the crown. In this study, we measured the relationships between height growth and diameter at breast height, die-back frequency and severity, vessel size and specific hydraulic conductivity of four evergreen (Senna siamea (Lamk) H.S. Irwin & Barneby, Jacaranda mimosifolia D. Don, Azadirachta indica A.H.L. Juss and Acacia gerrardii Benth.) and one deciduous (Melia volkensii Gürke) plantation tree species in Kenya, which has a conspicuous dry season. Die-back occurred readily in some species, but not in others. Senna siamea showed the highest specific hydraulic conductivity and the highest growth rate among the five species and was quite susceptible to die-back. Among species, height growth and specific hydraulic conductivity were positively correlated with vessel size and negatively correlated with die-back frequency, suggesting a trade-off between growth rate and drought tolerance. This implies that an adaptation to rapid growth under humid conditions leads to low drought tolerance. However, the deciduous tree Melia volkensii showed high specific hydraulic conductivity and growth, with no symptoms of die-back, implying that a mechanism associated with the deciduous habit results in drought avoidance by reducing the requirement for water during the dry season.

Acacia↗
PubMed2000

Depressed pollination in habitat fragments causes low fruit set.

In central New South Wales, Australia, flowers of Acacia brachybotrya and Eremophila glabra plants growing in linear vegetation remnants received less pollen than conspecifics in nearby reserves. Pollen supplementation increased fruit production by both species, indicating pollen limitation of fruit set. Together these observations explain why fruit production by these species was depressed in linear-strip populations relative to nearby reserves. This study confirms that habitat fragmentation can lead to decline in pollination and subsequent fruit set in wild plant populations. Disrupted pollination interactions of the kind documented in this study may offer a substantial challenge to the conservation of biodiversity in fragmented landscapes.

Acacia↗
PubMed1999

Sinorhizobium arboris sp. nov. and Sinorhizobium kostiense sp. nov., isolated from leguminous trees in Sudan and Kenya.

SDS-PAGE of total bacterial proteins was applied to the classification of 25 Sudanese and five Kenyan strains isolated from the root nodules of Acacia senegal and Prosopis chilensis. Twenty strains were also studied by multilocus enzyme electrophoresis (MLEE) and the whole 16S rRNA gene was sequenced from two strains representing the two major clusters. These results, together with the previously reported numerical taxonomy analysis, pulsed-field gel electrophoresis studies, DNA-DNA dot-blot hybridization, genomic fingerprinting using repetitive sequence-based PCR, DNA base composition analysis, DNA-DNA reassociation analysis, partial sequencing of the 16S rRNA gene and RFLP analysis of the amplified 16S rRNA gene, showed that all 30 strains belong to the genus Sinorhizobium. Two of the strains grouped with Sinorhizobium saheli and seven with Sinorhizobium terangae, while the rest did not cluster with any of the established species. The majority of the strains formed two phenotypically and genotypically distinct groups and we therefore propose that these strains should be classified as two new species, Sinorhizobium arboris sp. nov. and Sinorhizobium kostiense sp. nov.

Acacia↗
PubMed2003

Increasing the oxidative stress response allows Escherichia coli to overcome inhibitory effects of condensed tannins.

Tannins are plant-derived polyphenols with antimicrobial effects. The mechanism of tannin toxicity towards Escherichia coli was determined by using an extract from Acacia mearnsii (Black wattle) as a source of condensed tannins (proanthocyanidins). E. coli growth was inhibited by tannins only when tannins were exposed to oxygen. Tannins auto-oxidize, and substantial hydrogen peroxide was generated when they were added to aerobic media. The addition of exogenous catalase permitted growth in tannin medium. E. coli mutants that lacked HPI, the major catalase, were especially sensitive to tannins, while oxyR mutants that constitutively overexpress antioxidant enzymes were resistant. A tannin-resistant mutant was isolated in which a promoter-region point mutation increased the level of HPI by 10-fold. Our results indicate that wattle condensed tannins are toxic to E. coli in aerobic medium primarily because they generate H(2)O(2). The oxidative stress response helps E. coli strains to overcome their inhibitory effect.

Acacia↗
PubMed2004

Effect of condensed tannins on bacterial diversity and metabolic activity in the rat gastrointestinal tract.

The effect of dietary condensed tannins (proanthocyanidins) on rat fecal bacterial populations was ascertained in order to determine whether the proportion on tannin-resistant bacteria increased and if there was a change in the predominant bacterial populations. After 3 weeks of tannin diets the proportion of tannin-resistant bacteria increased significantly (P < 0.05) from 0.3% +/- 5.5% to 25.3% +/- 8.3% with a 0.7% tannin diet and to 47.2% +/- 5.1% with a 2% tannin diet. The proportion of tannin-resistant bacteria returned to preexposure levels in the absence of dietary tannins. A shift in bacterial populations was confirmed by molecular fingerprinting of fecal bacterial populations by denaturing gradient gel electrophoresis (DGGE). Posttreatment samples were generally still distinguishable from controls after 3.5 weeks. Sequence analysis of DGGE bands and characterization of tannin-resistant isolates indicated that tannins selected for Enterobacteriaceae and Bacteroides species. Dot blot quantification confirmed that these gram-negative bacterial groups predominated in the presence of dietary tannins and that there was a corresponding decrease in the gram-positive Clostridium leptum group and other groups. Metabolic fingerprint patterns revealed that functional activities of culturable fecal bacteria were affected by the presence of tannins. Condensed tannins of Acacia angustissima altered fecal bacterial populations in the rat gastrointestinal tract, resulting in a shift in the predominant bacteria towards tannin-resistant gram-negative Enterobacteriaceae and Bacteroides species.

Acacia↗
PubMed2005

Proapoptotic triterpene electrophiles (avicins) form channels in membranes: cholesterol dependence.

Avicins, a family of triterpenoid saponins from Acacia victoriae, can regulate the innate stress response in human cells. Their ability to induce apoptosis in transformed cells makes them potential anticancer agents. We report that avicins can form channels in membranes. The conductance reached a steady state after each addition, indicating a dynamic equilibrium between avicin in solution and in the membrane. The high power dependence (up to 10) of the membrane conductance on the avicin concentration indicates the formation of multimeric channels, consistent with the estimated pore radius of 1.1 nm. This radius is too small to allow protein flux across the mitochondrial outer membrane, a process known to initiate apoptosis. Channel formation is lost when avicin's amphipathic side chain is removed, implicating this as the channel-forming region. A small difference in this side chain results in strong cholesterol dependence of channel formation in avicin G that is not found in avicin D. In neutral membranes, avicin channels are nonselective, but negatively-charged lipids confer cation selectivity (5:1, K(+):Cl(-)), indicating that phospholipids form part of the permeation pathway. Avicin channels in the mitochondrial outer membrane may favor apoptosis by altering the potential across this membrane and the intermembrane space pH.

Acacia↗
PubMed2003

Assessment of management-dependent nutrient losses in tropical industrial tree plantations.

Industrial tree plantations in the tropics usually follow short rotations and intensive site management including slash and burn, and the use of heavy machinery. We attempt to quantify the implied nutrient losses (harvest export, erosion, slash and burn, leaching) in order to give plantation managers a chance to understand the significance of their planning and decisions. We used the scarce globally available information and a case study plantation in East Kalimantan, Indonesia (Acacia mangium and Eucalyptus deglupta). Adaptation involves problems and is discussed in some detail. Results are approximate only. Assuming a harvest volume of 200 m3 ha(-1), we assessed a loss of 427-680 kg ha(-1) N, 12-13 kg ha(-1) P, 178-252 kg ha(-1) Ca, 276-370 kg ha(-1) K, and 45-57 kg ha(-1) Mg per rotation. Of this overall loss, stand harvest accounted for 18-29% (N), 21-30% (P), 56-26% (K), 48-64% (Ca) and 22-37% (Mg). This means that the cumulative loss by erosion, slash and burn, and leaching exceeds that of the harvest. These losses can be influenced by management.

Acacia↗
PubMedDate not supplied

Improved stability of w/o/w multiple emulsions by addition of hydrophilic colloid components in the aqueous phases.

To improve the stability of w/o/w multiple emulsions of arachis and olive oil the stabilizing effect of cherry gum, in combination with acacia and gelatin, was examined. The outstanding film-forming properties of this gum having already been noted; the effect of its addition to the aqueous phases was measured by the coalescence of emulsion globules. The enhanced stability, as compared to controls, was achieved at a minimum concentration which liquid crystal-bearing interfacial films seem to appear. Creation of more coherent interfaces, inhibiting transfer of phases, could be the basis of the improved stability of the emulsion.

Acacia↗
PubMedDate not supplied

The influence of HLB on the encapsulation of oils by complex coacervation.

Microcapsules are used for the formulation of drug controlled release and drug targeting dosage forms. Encapsulated hydrophobic drugs are often applied as their solutions in plant oils. The uptake of the oils in the complex coacervate microcapsules can be improved by the addition of surfactants. In this study, soybean, olive and peanut oils were chosen as the representatives of plant oils. The well characterized complex coacervation of gelatin and acacia has been used to produce the microcapsules. The amount of encapsulated oil has been determined gravimetrically. The encapsulation of the oils was high (75-80%). When the surfactants with HLB values from 1.8 to 6.7 were used, the amount of encapsulated oil was high (65-85%). A significant decrease of the oil content in the microcapsules was found when Tween 61 with HLB = 9.6 had been added into the mixture. No oil was found inside the microcapsules from the coacervate emulsion mixture containing Tween 81 (HLB = 10) and Tween 80 (HLB = 15), respectively. The results of the experiment confirm the dependence of hydrophobic substance encapsulation on the HLB published recently for Squalan.

Acacia↗
PubMed2006

Medicinal plant extracts as anti-Escherichia coli O157:H7 agents and their effects on bacterial cell aggregation.

Ethanolic extracts of eight Thai medicinal plants (representing five families) that are used as traditional remedies for treating diarrhea were examined with a salt aggregation test for their ability to modulate cell surface hydrophobicity of enterohemorrhagic Escherichia coli strains, including E. coli O157:H7. Four of these medicinal plants, Acacia catechu, Peltophorum pterocarpum, Punica granatum, and Quercus infectoria, have high bacteriostatic and bactericidal activities. The ethanolic extract of Q. infectoria was the most effective against all strains of E. coli, with MICs of 0.12 to 0.98 mg/ml and MBCs of 0.98 to 3.91 mg/ml. The ethanolic extract of P. granatum had MICs of 0.49 to 1.95 mg/ml and MBCs of 1.95 to 3.91 mg/ml. Ethanolic extracts of Q. infectoria, P. pterocarpum, and P. granatum were among the most effective extracts against the two strains of E. coli O157:H7. The other four plants, Andrographis paniculata, Pluchia indica, Tamarindus indica, and Walsura robusta, did not have high bacteriostatic and bactericidal activities but were able to affect hydrophobicity characteristics on their outermost surface. All plants except Q. infectoria had some ability to increase cell surface hydrophobicity. There appears to be no correlation between antibacterial activity and cell aggregative properties.

Acacia↗
PubMed2001

The antimicrobial effects of seven different types of Asian chewing sticks.

There are various plants, which are used as chewing sticks in different parts of the world. Several studies have been reported on the antimicrobial effects of chewing sticks on oral bacteria. The aim of this study was to compare the antimicrobial effect of aqueous extract of seven different types of chewing sticks found in Pakistan and other Asian countries. The ditch plate method was used to test the antimicrobial activity of seven Asian chewing sticks. It was found that at there was antimicrobial effect on Streptococcus fecalis at 50% concentration of Kikar (Acacia arabica) from Pakistan and Arak (Salvadora persica) from Saudi Arabia. The inhibition zones up to 2 mm were found in those two chewing stick extracts. It is recommended that the chewing sticks will be a great help in developing countries with financial constraints and limited oral health care facilities for their populations.

Acacia↗
PubMedDate not supplied

Encapsulation of a lipid precursor, the eicosapentaenoic acid, to study the development of the Crassostrea gigas oyster flavours.

The present study is part of a larger project whose aim is to understand how the oyster Crassostrea gigas develops its aromas from a lipid precursor, the eicosapentaenoic acid (EPA), in glyceride form. The objective of this study is, therefore, to prepare an encapsulation process that will enable the bivalve to be supplied with this lipid precursor. The complex coacervation method was chosen as it gave the best compatible microcapsules with respect to the nutritional aspects of oyster (i.e. digestibility) and the environmental constraints (i.e. behaviour and stability in seawater). The aim of this study is to manufacture and optimize a process of complex coacervation, to obtain capsules made of gelatin and acacia gum with a size under 100 microm in diameter and containing very small drops of cod liver oil (rich in EPA). The preservation of these microcapsules in seawater has been confirmed.

Acacia↗