The proteinaceous components of the gum exudates from some phyllodinous Acacia species

Acacia gum exudates are proteinaceous polysaccharides; their protein content ranges from ca 0.2 to 45%.The data presented show that the amino acid compositions of the gums from 12 phyllodinous species (10 from Bentham's sub-series Uninerves racemosae, two from sub-series Juliflorae) also vary considerably, particularly in respect of their hydroxyproline content (55 residues per 1000 residues in A. aestivalis gum, 287 residues per 1000 in A. saliciformis gum). The proportions of some other amino acids, e.g. alanine, aspartic acid, proline and serine also vary considerably, but the proportions of others, e.g. cystine, methionine, histidine, threonine, tyrosine and valine, are remarkably constant. The amino acid composition of gums with a very low protein content (e.g. A. victoriae and A. mycrobotrya) is similar to that for a highly proteinaceous gum (A. tumida). There are, however, considerable differences between the amino acid compositions of the gums from A. saligna and A. pycnantha (South African and Western Australian specimens). This strengthens previous chemotaxonomic evidence, based on the polysaccharide parameters of their gums, that these two species are not as close taxonomically as was originally believed from morphological considerations.     

The gum exudates from some closely related Acacia species of the subseries Uninerves racemosae (section phyllodineae)

Australian gum specimens from Acacia aestivalis, A. chrysella, A. jennerae and A. microbotrya (five specimens differing slightly in some morphological characters) have been studied. These species, placed within Bentham's Series 1, subseries 6F (Uninerves racemosae) are closely related, forming part of the recognized A. microbotrya group. The five specimens from A. microbotrya show minor variations, similar in extent to those established previously for gums from other species. The gums from A. chrysella and A. jennerae are similar to those from A. microbotrya in chemical composition. The gum from A. aestivalis differs from those from A. microbotrya, A. chrysella and A. jennerae in two main respects: it is more acidic and has a much higher methoxyl content. Thus significant differences in gum composition can be shown by some species that differ only slightly in morphological characters. Data for the amino acid compositions of the proteinaceous components of the gums from A. aestivalis, A. jennerae and A. microbotrya, differ considerably from those for the gums from other species belonging to the Uninerves racemosae, e.g. A. saliciformis and A. xanthina, which are much more viscous and have higher proteinaceous contents containing much higher proportions of the amino acids commonly involved in linkages with sugars. Of the closely related species studied, A. aestivalis is closer to A. microbotrya than A.jennerae in terms of the amino acid compositions of their gums, a reversal in the relative affinities shown by their polysaccharide parameters. Thus amino acid compositions are of interest chemotaxonomically and also in terms of the tertiary structures of Acacia gum exudates.     

The gum exudates from Brachystegia and Julbernardia species

Analytical data are presented for the water-soluble gum exudates from Brachystegia glaucescens, B. spiciformis, and Julbernardia globiflora. They are acidic polysaccharides containing glucuronic acid, 4-O-methylglucuronic acid and galacturonic acid, together with galactose, minor amounts of arabinose, and relatively high proportions of rhamnose. The exudate from B. glaucescens is of particular interest in having high molecular weight, high intrinsic viscosity, and a high methoxyl content. The nitrogen content of all three gums is low, but amino acid analysis shows that proteinaceous components are involved, as in the gum exudates from other genera.     

The gum exudates from Chloroxylon swietenia,Sclerocarya caffra,Azadirachta indica and Moringa oleifera

Analytical data are presented for the polysaccharide and proteinaceous components of the gum exudates from Chloroxylon swietenia and Sclerocarya caffra, and for the amino acid compositions of the exudates from Azadirachta indica (two specimens) and Moringa oleifera. The gums from C. swietenia and S. caffra contain 4-O-methylglucuronic acid, glucuronic acid, galactose and arabinose; rhamnose is absent. Amino acid analysis shows that proteinaceous material is present in the gums from C. swietenia, S. caffra and M. oleifera despite their low nitrogen content. Hydroxyproline accounts for 28 % of the amino acid content of S. caffra gum. In contrast, A. indica gum has a high nitrogen content but contains very little hydroxyproline.     

The hydroxyproline content of gum exudates from several plant genera

Amino acid compositions are presented for the proteinaceous components of the gum exudates from Albizia glaberrima, A. sericocephala and A. anthelmintica; Aralia elata; Azadirachta indica; Entada africana; Grevillea robusta; Lannea humilis and L. schimperi; and Moringa oleifera. The gums from four of these genera (Albizia, Azadirachta, Grevillea and Moringa) contain low proportions, and the others contain high proportions, of hydroxyproline. High proportions of hydroxyproline were found previously in gum exudates from genera within the Leguminosae (Acacia, Astragalus and Prosopis), to which must now be added Entada and Leucaena. In contrast, however, Albizia spp. (Leguminosae) have low proportions of hydroxyproline, whereas the non-leguminous genera Aralia and Lannea have high proportions of hydroxyproline.     

Amino acid composition of gum exudates from some african Combretum terminalia and anogeissus species

Amino acid compositions are presented for the proteinaceous components of the gum exudates from Combretum glutinosum (syn. apiculatum), C. zeyheri, C. molle (syn. guenzii), C. psidioides (syn. grandifolium), C. obovatum, C. collinum (syn. binderanum), C. hartmannianum, C. fragrans (syn. ternifolium), Teminalia sericea and T. superba; and for Anogeissus schimperi. The principal amino acids common to these species are aspartic acid, alanine and glycine, but there are considerable variations; glutamic acid, histidine, lysine, proline, serine, threonine and valine are also major components of some of the species studied. The Combretaceae are therefore similar to the Sterculiaceae in containing very low proportions of hydroxyproline, which is the major amino acid component of the gums studied so far from genera within the Mimosoideae.     

Some Acacia gum exudates of the section Phyllodineae

Australian gum specimens from Acacia saliciformis, A. xanthina, A. rostellifera, A. murrayana (two specimens differing in the mode of initiation of gum exudation), A. georginae, A. cyclops, A. implexa, and an un-named species (Maslin ‘P31’) have been analysed. The first four of these are placed within Bentham's Series 1, subseries 6F, A. georginae within subseries 7E, and the remainder within subseries 7F. These data extend considerably the ranges of the analytical parameters reported previously for phyllodine species. The molecular weights of the gums from A. cyclops and A. implexa are much higher than those reported earlier for South African specimens; this may affect some taxonomic deductions based on their examination. The gum composition of A. saligna can no longer be regarded as atypical of a phyllodinous species; a suggestion that A. saligna should be transferred to the section Juliflorae may require reconsideration. The major difference between the specimens of gum from A. murrayana lies in their nitrogenous content. Data are reported for the amino acid compositions of the gums from A. saliciformis and A. xanthina.     

Gum polysaccharides from three Parkia species

Nigerian gum exudates from Parkia bicolor and P. biglobosa, and gum from the seed pods of P. pendula growing in Costa Rica have been analysed. The two gum exudates are proteinaceous and have closely similar physicochemical properties and compositions, with galactose, arabinose, glucuronic acid and 4-O-methylglucuronic acid as their constituent sugars; rhamnose is absent, and they are dextrorotatory. The gum from the seed pods of P. pendula contains the same constituent sugars in different proportions, and is laevorotatory. These data may be of interest in the continuing studies of plant-animal interactions and mechanisms of seed dispersal associated with the genus Parkia.     

The composition of the proteinaceous polysaccharides exuded by astragalus microcephalus,A. Gummifer and A. Kurdicus—The sources of turkish gum tragacanth

Gum tragacanth is a variable commodity because commercial samples may legitimately be admixtures, in any relative proportions, of the exudates from Asiatic Astragalus spp. Analytical data show that the exudates collected from the three major contributing Turkish spp., A. microcephalus, A. gummifer and A. kurdicus, differ extensively, particularly in terms of their fucose, xylose, galacturonic acid and methoxyl contents and in the relative proportions of their soluble (tragacanthin) and insoluble (bassorin) components. In addition, these three Astragalus exudates are shown to be proteinaceous polysaccharides; their amino acid compositions differ, particularly in terms of their hydroxyproline, histidine, aspartic acid and arginine content. In contrast, the amino acid compositions of the soluble and insoluble components of A. kurdicus do not differ extensively.     

The composition and properties of the gum exudates from Terminalia sericea and T. Superba

The gum polysaccharides from Terminalia sericea and T. superba have been analysed. They have a complex sugar composition, containing galacturonic, glucuronic, and 4-O-methylglucuronic acids as well as galactose, arabinose, rhamnose, mannose and xylose. The exudates from T. sericea and T. superba are remarkably similar in composition, particularly with respect to their proportions of neutral sugars and total uronic acid content, although T. sericea gum contains considerably more 4-O-methylglucuronic acid than T. superba. Both gums are very viscous and dissolve readily to give solutions of good colour.!!     

Analytical comparison of gums from Acacia hebeclada and other gummiferae species

Analysis of the arabinogalactan-protein isolated from a specimen of Acacia hebeclada gum has shown major differences in composition between this and a specimen previously examined in another laboratory. In its much lower proportions of protein and uronic acid, and higher arabinose content, the present specimen of A. hebeclada gum resembles more closely gum from the taxonomically related species A. tortilis, this similarity extending to the modes of linkage of the constituent sugar and uronic acid residues. The hydroxyproline content of the protein moiety is also close to that in A. tortilis gum. The wide variation in composition between different specimens of A. hebeclada gum is comparable with that of the gums of A. karroo and A. erioloba, from the same series (Gummiferae Benth.).     

Hydrolytic fragmentation of seed gums under microwave irradiation

The seed gum solutions of Ipomoea purga, Ipomoea palmata, Ipomoea dasysperma, Cyanaposis tetragonolobus (Guar gum) and Crotolaria medicaginea were microwave (MW) irradiated and their degradation to oligo and monosaccharides was investigated. The gum solutions were fragmented into oligosaccharides/constituent monosaccharides depending upon the length of MW exposure in presence of catalytic amount of mineral acid or even when no acid was used. A mechanism for the microwave induced hydrolytic degradation of the seed gums has been proposed. The MW exposure time required for the partial and complete degradation of the gums was found dependent on the types of the linkages and degree of the branching present in the gums.     

The composition of acacia gum exudates from species of the subseries Juliflorae

An analytical study has been made of gum specimens from Acacia auriculiformis (two specimens), A.holosericea, A.mangium, A.leptostachya and A.pubifolia, which belong to subseries Juliflorae of the Series Phyllodineae. These gums appear to be more proteinaccous, more acidic and more viscous, with higher methoxyl contents and higher molecular weights but with lower proportions of rhamnose and arabinose, than the majority of Acacia gums studied so far.     

Spatial and temporal variation in islands of fertility in the Sonoran Desert

In many arid and semi-arid ecosystems, canopy trees and shrubs have a strong positive influence on soil moisture and nutrient availability, creating islands of fertility where organic matter and nutrients are high relative to areas outside the canopy. Previous studies of canopy effects on soil processes have rarely considered how landscape context may modulate these effects. We measured the effects of velvet mesquite trees (Prosopis velutina) on soil moisture and the biogeochemistry of nitrogen at different positions along a topographic gradient from upland desert to riparian zone in the Sonoran Desert of central Arizona. We also examined how landscape position and patterns of precipitation interact to determine the influence of P. velutina on soil moisture, N availability assessed using ion exchange resins, net N mineralization and net nitrification, and microbial biomass C and N. P. velutina clearly created islands of fertility with higher soil organic matter, net N mineralization and net nitrification rates, and microbial biomass under mesquite canopies. These effects were consistent across the landscape and showed little temporal variability. Magnitude and direction of effect of mesquite on soil moisture changed with landscape position, from positive in the upland to negative in the terrace, but only when soil moisture was >4%. Resin N showed responses to mesquite that depended on precipitation and topographic position, with highest values during wet seasons and under mesquite on terraces. We suggest changes in proximity of P. velutina to groundwater lead to shifts in biogeochemical processes and species interactions with change in landscape position along a topographic gradient.     

Seedling Responses to Water Pulses in Shrubs with Contrasting Histories of Grassland Encroachment

Woody plant encroachment into grasslands has occurred worldwide, but it is unclear why some tree and shrub species have been markedly more successful than others. For example, Prosopis velutina has proliferated in many grasslands of the Sonoran Desert in North America over the past century, while other shrub species with similar growth form and life history, such as Acacia greggii, have not. We conducted a glasshouse experiment to assess whether differences in early seedling development could help explain why one species and not the other came to dominate many Sonoran Desert grasslands. We established eight watering treatments mimicking a range of natural precipitation patterns and harvested seedlings 16 or 17 days after germination. A. greggii had nearly 7 times more seed mass than P. velutina, but P. velutina emerged earlier (by 3.0±0.3 d) and grew faster (by 8.7±0.5 mg d⁻¹). Shoot mass at harvest was higher in A. greggii (99±6 mg seedling⁻¹) than in P. velutina (74±2 mg seedling⁻¹), but there was no significant difference in root mass (54±3 and 49±2 mg seedling⁻¹, respectively). Taproot elongation was differentially sensitive to water supply: under the highest initial watering pulse, taproots were 52±19 mm longer in P. velutina than in A. greggii. Enhanced taproot elongation under favorable rainfall conditions could give nascent P. velutina seedlings growth and survivorship advantages by helping reduce competition with grasses and maintain contact with soil water during drought. Conversely, A. greggii''s greater investment in mass per seed appeared to provide little return in early seedling growth. We suggest that such differences in recruitment traits and their sensitivities to environmental conditions may help explain ecological differences between species that are highly similar as adults and help identify pivotal drivers of shrub encroachment into grasslands.     

The structure of Lannea humilis gum

Lannea humilis trees exude a water-soluble gum polysaccharide containing galactose (75%), arabinose (11%), rhamnose (2%), and uronic acids (12%). Three aldobiouronic acids are present (chromatographic analysis), namely 4-O-(α-D-galactopyranosyluronic acid)-D-galactose, 6-O-(β-D-glucopyranosyluronic acid)-D-galactose, and 6-O-(4-O-methyl-β-D-glucopyranosyluronic acid)-D-galactose. Linkage analysis of degraded gums A and B, obtained by controlled, acid hydrolysis, gave (chromatographic analysis) 3-O-β-L-arabinofuranosyl-L-arabinose, 3-O-β-L-arabinopyranosyl-L-arabinose, 3-O-α-D-galactopyranosyl-L-arabinose, 3-O-β-D-galactopyranosyl-D-galactose, and 6-O-β-D-galactopyranosyl-D-galactose. Degraded gums A and B were examined by methylation analysis, and the former was subjected to a Smith-degradation, giving degraded gum C, which was studied by linkage and methylation analysis. The O-methyl derivative of the whole gum was prepared (a) by the Haworth and Purdie procedures, and (b) by the sodium hydride-methyl iodide-methyl sulphoxide technique. Both products were examined, after methanolysis, by g.l.c.: 2,3,4-tri-O-methyl-L-rhamnose; 2,3,5- and 2,3,4-tri- and 2,5-di-O-methyl-L-arabinose; 2,3,4,6-tetra-, 2,3,6-, 2,4,6- and 2,3,4-tri-, 2,6- and 2,4-di-, and 2-O-methyl-D-galactose; 2,3,4-tri-O-methyl-D-glucuronic acid and 2,3,4-tri-O-methyl-D-galacturonic acid were identified. The whole gum was subjected to four successive Smith-degradations giving Polysaccharides I–IV, which were examined by linkage and methylation analysis. Polysaccharide IV is a branched galactan; the arabinose-containing sidechains in L. humilis gum therefore do not contain more than four residues, and only a few of that length occur. The evidence obtained indicates that the gum molecules are very highly branched. The galactan framework consists of short chains of β-(1→3)-linked D-galactose residues, branched and interspersed with β-(1→6)-linkages. To positions 3 and 6 of this framework are attached either single D-galactose end-groups or short side-chains of D-galactose or of L-arabinose residues, and three aldobiouronic acids. A possible structural fragment that shows these features is proposed.     

Structural features of the gum exudates from some Acacia species of the series Phyllodineae and Botryocephalae

Smith degradation of each of the polydisperse, gum polysaccharides from Acacia pycnantha, A. difformis, A. filicifolia, and A. podalyriaefolia, for which molecular-weight distributions have been measured by gel-permeation chromatography, gives, in good yield, a methanol-insoluble polysaccharide that shows a single peak on examination by this technique. The molecular weights of the Smith-degraded polysaccharides are close to the values expected if the respective gum polysaccharides, on losing periodate-vulnerable, peripheral sugar residues were to be split also at regular intervals between the otherwise (1→3)-linked d-galactose chains. The structures of these gums, which are similar in many respects, conform to the pattern shown recently to occur in the gum of A. baileyana.     

Lipids of fish parasites and their hosts: fatty acids of phospholipids of Paratenuisentis ambiguus and its host eel (Anguilla anguilla)

The fatty acid composition of various phospholipid classes, e.g. phosphatidylcholines, phosphatidylethanolamines, phosphatidylserines and sphingomyelins, of the fish endoparasite Paratenuisentis ambiguus and of intestinal tissue of its host, eel (Anguilla anguilla), were investigated. Phospholipids from parasite and infected host intestine show considerable differences in the fatty acid compositions. High proportions of saturated long-chain and very long-chain acyl moieties were found in phosphatidylcholines, ethanolamines and serines of the parasite. Membrane phospholipids of P. ambiguus contain remarkably high proportions of polyunsaturated acyl moieties, in particular eicosapentaenoyl moieties (20:5 n-3), which undoubtedly originate from aquatic feed or host intestine. It is suggested that the parasite's membranes are stabilized by incorporation of high proportions of saturated long-chain and very long-chain fatty acids to counterbalance the destabilizing effects of the polyunsaturated fatty acids.     

Structural studies of sapote (Sapota achras) gum

Sapote gum contains residues of L-arabinose (pyranose and furanose), D-xylose, D-glucuronic acid, and 4-O-methyl-D-glucuronic acid in the ratio 1.0:2.8:0.48:0.52. The two uronic acids were conveniently determined by reducing the carboxyl functions with lithium borohydride and measuring the ratio of D-glucose to 4-O-methyl-D-glucose. Periodate oxidation of the carboxyl-reduced gum gave inter alia 2-O-methyl-D-erythritol and 4-O-methyl-D-glucose in amounts suggesting that 37% of the 4-O-methyl-D-glucuronic acid residues are unsubstituted in the polysaccharide. Acetolysis of the carboxyl-reduced gum gave O-α-D-glucopyranosyl-(1→2)-(4-O-β-D-xylopyranosyl)_0,1,2,-D-xylose, a hitherto undescribed series of oligosaccharides, together with 2-O-(4-O-methyl-α-D-glucopyranosyl)-D-xylose. Methylation confirmed that sapote gum has a highly branched structure, and commercial xylanases did not depolymerize the gum. An α-L-arabinofuranosidase liberated a substantial part of the arabinose residues. Sapote gum is a member of the uncommon class of plant gums having a D-xylose backbone and structurally resembles brea gum.