Mimosa Scabrella Research Articles

Traditional fallow systems of the Americas

Six neotropical traditional fallow systems are described: 1) enriched fallows of the Amazon, 2) Babassu palm (Orbignya phalerata Mart.) forests of central and northern Brazil, 3) bracatinga (Mimosa scabrella Benth) improved fallow of southeastern Brazil, 4) carbon negro (Mimosa tenuiflora Willd.) fallow of the wet-dry zone of Mesoamerica, 5) frijolillo (Senna guatemalensis Donn. Smith) of high-elevation zones in southern Honduras, and 6) caragra (Lippia torresii) fallow of humid zones of Costa Rica. These systems include both biologically and economically enriched fallows. Some (e.g., the enriched fallows of the Amazon) require a considerable degree of human intervention, while others (e.g., the bracatinga and carbon negro fallows) seem to form with little human encouragement, following the burn in shifting cultivation systems. Some of the systems (e.g., frijolillo and caragra) are quite site-specific and have a limited distribution; others (e.g., babassu, bracatinga, and carbon negro) occur over large areas and could be adapted to considerable areas in the Americas. As economic analyses are generally lacking, it is unclear what benefits would be achieved from a wider use of these systems. Most of the biologically enriched fallows seem able to maintain low yields of food crops at low input levels. Some of the economically enriched fallows seem able to produce higher economic returns.

QUALIDADE DE LUZ E GERMINAÇÃO DE SEMENTES DE ESPÉCIES ARBÓREAS TROPICAIS.

O entendimento da complexa regeneração do ecossistema de floresta tropical passa pela associação da germinação com o fator luz. Assim, o presente estudo investigou a germinação das sementes de quatro espécies arbóreas tropicais, pertencentes a diferentes estágios sucessionais, quando submetidas a ambientes com luzes vermelha, vermelha-distante, azul, branca e também escuro. As sementes das espécies Mimosa scabrdla(pioneira), Chorisia epeciosa, Tabebuia avellanedae(secundárias) e Esenbeckia leiocarpa (clímax) germinaram melhor no escuro, seguido de vermelho, azul, branco e vermelho-distante. A análise conjunta dos dados, tratando cada câmara de luz como um ambiente, revelou dependência entre a germinação das sementes e os ambientes de luz. Essa interação espécie x luz, ao ser desdobrada, confirmou diferenças significativas das luzes na germinação das espécies.

Study of solution properties of galactomannan from the seeds of Mimosa scabrella

The rheological properties of the galactomannan from the seeds of a member of the Leguminosae have been studied. The sample used had a mannose/galactose ratio close to 1 and an intrinsic viscosity of 900 ml/g. The viscosity results are characteristic of a random coil polymer with a critical concentration c ∗ = 2·6/[η] which is similar to the values found for polystyrene and polystyrenesulphonate, but higher than the value obtained for more rigid polysaccharides. The slope of the logarithmic plot of the specific viscosity measured at zero shear rate against c[ η] in the semi-dilute regime was 4·2, a value in agreement with the theoretical predictions for linear polymers interacting by purely topological entanglements. The viscoelastic behaviour was lower than that found for solutions of other galactomannans and this and the less severe dependence of the viscosity on the coil overlap parameter is probably due to lower interactions because of the high galactose content.

Highly uneven distribution of O-acetyl groups in the acidic d-xylan of Mimosa scabrella (bracatinga)

The acidic O-acetyl- d-xylan of Mimosa scabrella contains xylose, 4- O-methylglucuronic acid, and O-acetyl groups in the molar ratios of 60:7:33 and, when subjected to controlled Smith degradation, provided xylosyl-, xylobiosyl-, xylotriosyl-, and xylotetraosyl-glycerol, as well as glycerol. Their proportions differed greatly from that which would arise from xylopyranosyl units substituted regularly with O-acetyl groups. In order to avoid ambiguities arising from resistance of some of the xylosyl units by substitution with 4- O-methylglucuronic acid, the O-acetylxylan was converted into a partly O-methylated polysaccharide having O-methyl groups with similar positions of substitution. Two successive Smith degradations were carried out, and the two sets of partly O-methylated derivatives resulting were identified by f.a.b.-m.s. The highly uneven distribution of O-acetyl groups along the xylan main-chain was confirmed, with the highest number of consecutive O-acetyl and 4- O-methylglucuronic acid substituents being six, and five O-acetyl substituents alone. 4- O-Methylglucuronic acid units were not substituted.

Entry of Rhizobia into Roots of Mimosa scabrella Bentham Occurs between Epidermal Cells

The nitrogen-fixing symbiosis between Mimosa scabrella and Rhizobium Br 3454 was initiated by an infection sequence consisting of (a) surface colonization of roots; (b) penetration of mucigel and primary layers of radial walls of epidermal cells; (c) further penetration through primary wall layers and intercellular air spaces; (d) occasional intracellular penetration of epidermal and cortical cells, always occurring from a boundary between two neighbouring cells. Root hairs, when present, were never seen to be infected by the well-known infection thread mechanism, nor were infections seen to occur through wounds. This newly described method of infection may be common in legumes.

Ureide production by N 2-fixing and non-N 2-fixing leguminous trees

Xylem-sap and stem and leaf extracts from 35 species, comprising 14 genera, of leguminous trees were analyzed for ureides, nitrate and α-amino acids. Trees were either inoculated with Rhizobium or fertilized with NH 4NO 3. The dominant form of soluble N in stem and leaf extracts and xylem sap was 2-amino acids. Certain non-N 2-fixing species, i.e. Tamarindus indica and Adenantherapavonina, produced significant amounts of ureides. Several N 2-fixing species. Mimosa scabrella, Sesbania grandiflora. Acacia mearnsii and Gliricida sepium, grown on mineral-N had higher absolute amounts of ureides in both extracts and exudates than did most nodulated species. Nodulated A. meamsii and S. grandiflora, had the highest amounts of ureides in xylem sap. The relative abundance of ureides in stem and leaf extracts was lower than in xylem sap, but was correlated. Results indicated that the presence of ureides, per se, was not a reliable indicator of N 2-fixing activity. Moreover, the relative abundance of ureides in most of the species tested was too low to use as a presumptive test for, or as a means of, estimating N 2 fixation.

Location of O-acetyl groups in the acidic d-xylan of mimosa scabrella (bracatinga). A study of O-acetyl group migration

Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga ( Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0–5° followed by extraction with cold ethanol, gave a soluble O-acetylated 4- O-methyl- d-glucurono- d-xylan having (1→4)-linked β- d-xylopyranosyl residues that were unsubstituted (65%) and 2- O-(14%), 3- O- (16%), and 2,3-di- O-acetylated (5%), as determined by methylation analysis. Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups. By comparison with synthetic, partly O-acetylated d-xylans of known composition, 13C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70°. Methyl 2- O-acetyl-4- O-methyl-β- d-xylopyranoside ( 6) was also unaffected by aqueous chlorine. O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl- d-xylans. The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70° for solutions in D 2O and (CD 3) 2SO, respectively.