RESUMO
Seed water imbibition is critical to seedling establishment in tropical forests. The seeds of the neotropical tree Hymenaea courbaril have no oil reserves and have been used as a model to study storage cell wall polysaccharide (xyloglucan - XyG) mobilization. We studied pathways of water imbibition in Hymenaea seeds. To understand seed features, we performed carbohydrate analysis and scanning electron microscopy. We found that the seed coat comprises a palisade of lignified cells, below which are several cell layers with cell walls rich in pectin. The cotyledons are composed mainly of storage XyG. From a single point of scarification on the seed surface, we followed water imbibition pathways in the entire seed using fluorescent dye and NMRi spectroscopy. We constructed composites of cellulose with Hymenaea pectin or XyG. In vitro experiments demonstrated cell wall polymer capacity to imbibe water, with XyG imbibition much slower than the pectin-rich layer of the seed coat. We found that water rapidly crosses the lignified layer and reaches the pectin-rich palisade layer so that water rapidly surrounds the whole seed. Water travels very slowly in cotyledons (most of the seed mass) because it is imbibed in the XyG-rich storage walls. However, there are channels among the cotyledon cells through which water travels rapidly, so the primary cell walls containing pectins will retain water around each storage cell. The different seed tissue dynamic interactions between water and wall polysaccharides (pectins and XyG) are essential to determining water distribution and preparing the seed for germination.
RESUMO
Soybean plants of the variety 'MG/BR Conquista' were grown in open top chambers, simulating elevated CO2 concentration ([CO2]) and high temperature under the following treatments: 1) ambient [CO2] and ambient temperature (Amb); 2) elevated [CO2] (eCO2) and ambient temperature (Elev); 3) ambient [CO2] and high temperature (Amb/Temp); 4) elevated CO2 and high temperature (Elev/Temp). The aim was to evaluate responses to elevated [CO2] and high temperature, with focus on plant development and seed yield, and composition. Elev stimulated grain yield and Amb/Temp had opposite effect. Several biochemical parameters were affected by Amb/Temp, most of them reversed by simultaneous application of Elev. The oil obtained with Elev/Temp had lower degree of unsaturation. A network of relationships among biochemical parameters of grains at three developmental stages revealed that Amb/Temp and Elev/Temp affect significantly both carbohydrate and lipid metabolisms. No significant difference was obtained comparing networks corresponding to Amb and Elev/Temp.
Assuntos
Biomassa , Dióxido de Carbono/farmacologia , Glycine max/efeitos dos fármacos , Carboidratos/química , Carbono/química , Carbono/metabolismo , Grão Comestível/metabolismo , Ácidos Graxos/química , Ácidos Graxos/metabolismo , Nitrogênio/química , Nitrogênio/metabolismo , Sementes/efeitos dos fármacos , Sementes/metabolismo , Glycine max/química , Glycine max/metabolismo , TemperaturaRESUMO
Background and Aims: Aerenchyma develops in different plant organs and leads to the formation of intercellular spaces that can be used by the plant to transport volatile substances. Little is known about the role of cell walls in this process, although the mechanism of aerenchyma formation is known to involve programmed cell death and some cell wall modifications. We assessed the role that cell wall-related mechanisms might play in the formation of aerenchyma in sugarcane roots. Methods: Sections of roots (5 cm) were subjected to microtomography analysis. These roots were divided into 1-cm segments and subjected to cell wall fractionation. We performed analyses of monosaccharides, oligosaccharides and lignin and glycome profiling. Sections were visualized by immunofluorescence and immunogold labelling using selected monoclonal antibodies against polysaccharide epitopes according to the glycome profiles. Key Results: During aerenchyma formation, gas spaces occupied up to 40 % of the cortex cross-section within the first 5 cm of the root. As some of the cortex cells underwent dissolution of the middle lamellae, leading to cell separation, cell expansion took place along with cell death. Mixed-linkage ß-glucan was degraded along with some homogalacturonan and galactan, culminating in the formation of cell wall composites made of xyloglucan, arabinoxylans, cellulose and possibly lignin. Conclusion: The composites formed seem to play a role in the physical-chemical properties of the gas chambers, providing mechanical resistance to forces acting upon the root and at the same time decreasing permeability to gases.
Assuntos
Raízes de Plantas/metabolismo , Saccharum/metabolismo , Parede Celular/metabolismo , Celulose/metabolismo , Lignina/metabolismo , Raízes de Plantas/crescimento & desenvolvimento , Polissacarídeos/metabolismo , Saccharum/crescimento & desenvolvimentoRESUMO
During seedling establishment, cotyledons of the rain forest tree Hymenaea courbaril mobilize storage cell wall xyloglucan to sustain growth. The polysaccharide is degraded and its products are transported to growing sink tissues. Auxin from the shoot controls the level of xyloglucan hydrolytic enzymes. It is not yet known how important the expression of these genes is for the control of storage xyloglucan degradation. In this work, partial cDNAs of the genes xyloglucan transglycosylase hydrolase (HcXTH1) and beta-galactosidase (HcBGAL1), both related to xyloglucan degradation, and two other genes related to sucrose metabolism [alkaline invertase (HcAlkIN1) and sucrose synthase (HcSUS1)], were isolated. The partial sequences were characterized by comparison with sequences available in the literature, and phylogenetic trees were assembled. Gene expression was evaluated at intervals of 6 h during 24 h in cotyledons, hypocotyl, roots, and leaves, using 45-d-old plantlets. HcXTH1 and HcBGAL1 were correlated to xyloglucan degradation and responded to auxin and light, being down-regulated when transport of auxin was prevented by N-1-naphthylphthalamic acid (NPA) and stimulated by constant light. Genes related to sucrose metabolism, HcAlkIN1 and HcSUS1, responded to inhibition of auxin transport in consonance with storage mobilization in the cotyledons. A model is proposed suggesting that auxin and light are involved in the control of the expression of genes related to storage xyloglucan mobilization in seedlings of H. courbaril. It is concluded that gene expression plays a role in the control of the intercommunication system of the source-sink relationship during seeding growth, favouring its establishment in the shaded environment of the rain forest understorey.
Assuntos
Regulação da Expressão Gênica de Plantas , Glucanos/metabolismo , Hymenaea/genética , Chuva , Plântula/crescimento & desenvolvimento , Plântula/genética , Árvores/genética , Xilanos/metabolismo , Actinas/metabolismo , Transporte Biológico/efeitos da radiação , DNA Complementar/genética , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Genes de Plantas , Glucosiltransferases/genética , Glicosiltransferases/genética , Hymenaea/enzimologia , Hymenaea/crescimento & desenvolvimento , Hymenaea/efeitos da radiação , Ácidos Indolacéticos/metabolismo , Luz , Filogenia , Plântula/efeitos da radiação , Árvores/enzimologia , Árvores/crescimento & desenvolvimento , Árvores/efeitos da radiação , beta-Frutofuranosidase/genética , beta-Galactosidase/genéticaRESUMO
Beta-galactosidases are enzymes that can be found in most living beings and in the plant kingdom its activity and genes have been detected in several tissues such as ripening fruits, developing leaves and flowers and storage tissues such as cotyledons. In plants, their activities are usually associated with the secondary metabolism or with oligosaccharide or polysaccharide degradation. Polysaccharide specific beta-galactosidases include beta-galactanases, which attack pectic polymers and beta-galactosidases that attack xyloglucans (XG). In the present work we purified an XG-specific beta-galactosidase (named hcbetagal) from cotyledons of developing seedlings of Hymenaea courbaril, a legume tree from the Neotropical region of the world. The enzyme has a molecular weight of 52-62 kDa and was shown to attack specifically xyloglucan oligosaccharides (XGOs) but not the polymer. It has a pH optimum between 3 and 4 and at this pH range the enzyme increases activity linearly up to 50 degrees C. Kinetic studies showed that hcbetagal is inhibited competitively by free galactose (K(i) = 3.7). The biochemical properties of hcbetagal as a whole suggest that it is involved in storage xyloglucan mobilisation during seedling development. Its high specificity towards XGOs, the low pH optimum and the fact that it is inhibited by its product (galactose) suggest that hcbetagal might be one of the biochemical control points in xyloglucan catabolism in vivo. A possible relationship with functional stability of the wall during cell death as cotyledons undergo senescence is discussed.
Assuntos
Cotilédone/enzimologia , Hymenaea/enzimologia , Proteínas de Plantas/química , Proteínas de Plantas/isolamento & purificação , beta-Galactosidase/química , beta-Galactosidase/isolamento & purificação , Morte Celular/fisiologia , Parede Celular/enzimologia , Senescência Celular/fisiologia , Glucanos/química , Glucanos/metabolismo , Concentração de Íons de Hidrogênio , Peso Molecular , Proteínas de Plantas/metabolismo , Xilanos/química , Xilanos/metabolismo , beta-Galactosidase/metabolismoRESUMO
The present study assessed the fruiting pattern, bird foraging behavior, and sugar content of ripe fruits of two sympatric species of Rubiaceae (Psychotria brasiliensis and P. nuda). This study was carried out in an Atlantic forest area on Ilha Grande, RJ, between August 1998 and July 1999. Fruit production occurred year round, with a peak of mature P. brasiliensis fruits in December 1998 and another of P. nuda in February of 1999. Lipaugus lanioides (Cotingidae), Baryphtengus ruficapillus (Momotidae) and Saltator similis (Emberizidae) made the most frequent foraging visits to fruiting P. brasiliensis, so that L. lanioides and B. ruficapillus removed the fruits with sallying maneuvers while S. similis gleaned the fruits. Lipaugus lanioides was by far the most important consumer, and potentially the main disperser of P. brasiliensis. Birds of this genus are heavy frugivores in the tropical forests and are widely assumed to be important seed dispersers. The fruits were analyzed quantitatively and qualitatively in relation to the amounts of sucrose and starch. Psychotria brasiliensis (the visited species) showed the smallest quantity of sucrose and the highest amount of starch. These findings suggest that what may influence the birds' choice of fruit is the proportion of starch in the Psychotria species studied here rather than the carbohydrate composition.
Assuntos
Aves/fisiologia , Carboidratos/análise , Comportamento Alimentar/fisiologia , Frutas/química , Psychotria , Animais , Aves/classificação , Brasil , Cromatografia Líquida de Alta Pressão , Cromatografia por Troca Iônica , SementesRESUMO
Os objetivos deste trabalho foram monitorar o padrão de frutificação, o comportamento de forrageamento de aves e o conteúdo de açúcares em frutos maduros de duas espécies simpátricas de Rubiaceae (Psychotria brasiliensis e P. nuda). O estudo foi realizado em área de Floresta Atlântica, na lha Grande, RJ, entre agosto de 1998 e julho de 1999. A frutificação ocorreu durante todo o ano com um pico de frutos maduros em dezembro de 1998 para P. brasiliensis e outro em fevereiro de 1999 para P. nuda. Lipaugus lanioides (Cotingidae), Baryphtengus ruficapillus (Momotidae) e Saltator similis (Emberizidae) foram os principais consumidores dos frutos de P. brasiliensis, sendo que L. lanioides e B. ruficapillus removeram os frutos adejando, enquanto S. similis os alcançou pousado nas plantas. Lipaugus lanioides foi o consumidor de frutos mais importante e potencialmente foi o principal dispersor das sementes de P. brasiliensis. As aves deste gênero estão entre os principais frugívoros especialistas de florestas tropicais e amplamente consideradas como importantes agentes dispersores de sementes. Os frutos foram analisados qualitativa e quantitativamente em relação às quantidades de açúcares livres e amido. A espécie visitada (P. brasiliensis) apresentou a menor quantidade de sacarose e a maior quantidade de amido. Os resultados sugerem que o consumo diferencial de frutos por espécies de aves não é influenciado pela composição de carboidratos, mas possivelmente pela proporção de amido nos frutos das espécies de Psychotria estudadas.
Assuntos
Animais , Aves/fisiologia , Carboidratos/análise , Comportamento Alimentar/fisiologia , Frutas/química , Psychotria , Brasil , Aves/classificação , Cromatografia Líquida de Alta Pressão , Cromatografia por Troca Iônica , SementesRESUMO
Beta-glucans are soluble fibers with physiological functions, such as interference with absorption of sugars and reduction of serum lipid levels. The objective of the present study was to analyze the distribution of beta-glucans in different tissues of the African grass species Rhynchelytrum repens and also to evaluate their hypoglycemic activity. Leaf blades, sheaths, stems, and young leaves of R. repens were submitted to extraction with 4 M KOH. Analysis of the fractions revealed the presence of arabinose, glucose, xylose, and traces of rhamnose and galactose. The presence of beta-glucan in these fractions was confirmed by hydrolyzing the polymers with endo-beta-glucanase from Bacillus subtilis, followed by HPLC analysis of the characteristic oligosaccharides produced. The 4 M KOH fractions from different tissues were subjected to gel permeation chromatography on Sepharose 4B, with separation of polysaccharides with different degrees of polymerization, the highest molecular mass (above 2000 kDa) being found in young leaves. The molecular mass of the leaf blade polymers was similar (250 kDa) to that of maize coleoptile beta-glucan used for comparison. The 4 M KOH fraction injected into rats with streptozotocin-induced diabetes showed hypoglycemic activity, reducing blood sugar to normal levels for approximately 24 h. This performance was better than that obtained with pure beta-glucan from barley, which decreased blood sugar levels for about 4 h. These results suggest that the activity of beta-glucans from R. repens is responsible for the use of this plant extract as a hypoglycemic drug in folk medicine.
Assuntos
Diabetes Mellitus Experimental/tratamento farmacológico , Hipoglicemiantes/farmacologia , Poaceae/química , Polissacarídeos/farmacologia , beta-Glucanas/farmacologia , Animais , Cromatografia Líquida de Alta Pressão , Hipoglicemiantes/isolamento & purificação , Masculino , Extratos Vegetais/farmacologia , Polissacarídeos/isolamento & purificação , Ratos , Ratos Wistar , beta-Glucanas/isolamento & purificaçãoRESUMO
ß-Glucans are soluble fibers with physiological functions, such as interference with absorption of sugars and reduction of serum lipid levels. The objective of the present study was to analyze the distribution of ß-glucans in different tissues of the African grass species Rhynchelytrum repens and also to evaluate their hypoglycemic activity. Leaf blades, sheaths, stems, and young leaves of R. repens were submitted to extraction with 4 M KOH. Analysis of the fractions revealed the presence of arabinose, glucose, xylose, and traces of rhamnose and galactose. The presence of ß-glucan in these fractions was confirmed by hydrolyzing the polymers with endo-ß-glucanase from Bacillus subtilis, followed by HPLC analysis of the characteristic oligosaccharides produced. The 4 M KOH fractions from different tissues were subjected to gel permeation chromatography on Sepharose 4B, with separation of polysaccharides with different degrees of polymerization, the highest molecular mass (above 2000 kDa) being found in young leaves. The molecular mass of the leaf blade polymers was similar (250 kDa) to that of maize coleoptile ß-glucan used for comparison. The 4 M KOH fraction injected into rats with streptozotocin-induced diabetes showed hypoglycemic activity, reducing blood sugar to normal levels for approximately 24 h. This performance was better than that obtained with pure ß-glucan from barley, which decreased blood sugar levels for about 4 h. These results suggest that the activity of ß-glucans from R. repens is responsible for the use of this plant extract as a hypoglycemic drug in folk medicine.
Assuntos
Animais , Masculino , Ratos , Diabetes Mellitus Experimental/tratamento farmacológico , Hipoglicemiantes/farmacologia , Poaceae/química , Polissacarídeos/farmacologia , beta-Glucanas/farmacologia , Cromatografia Líquida de Alta Pressão , Hipoglicemiantes/isolamento & purificação , Extratos Vegetais/farmacologia , Polissacarídeos/isolamento & purificação , Ratos Wistar , beta-Glucanas/isolamento & purificaçãoRESUMO
Synthases of cellulose, chitin, hyaluronan, and all other polymers containing (1-->4)beta-linked glucosyl, mannosyl and xylosyl units have overcome a substrate orientation problem in catalysis because the (1-->4)beta-linkage requires that each of these sugar units be inverted nearly 180 degrees with respect to its neighbors. We and others have proposed that this problem is solved by two modes of glycosyl transfer within a single catalytic subunit to generate disaccharide units, which, when linked processively, maintain the proper orientation without rotation or re-orientation of the synthetic machinery in 3-dimensional space. A variant of the strict (1-->4)beta-D-linkage structure is the mixed-linkage (1-->3),(1-->4)beta-D-glucan, a growth-specific cell wall polysaccharide found in grasses and cereals. beta-Glucan is composed primarily of cellotriosyl and cellotetraosyl units linked by single (1-->3)beta-D-linkages. In reactions in vitro at high substrate concentration, a polymer composed of almost entirely cellotriosyl and cellopentosyl units is made. These results support a model in which three modes of glycosyl transfer occur within the synthase complex instead of just two. The generation of odd numbered units demands that they are connected by (1-->3)beta-linkages and not (1-->4)beta-. In this short review of beta-glucan synthesis in maize, we show how such a model not only provides simple mechanisms of synthesis for all (1-->4)beta-D-glycans but also explains how the synthesis of callose, or strictly (1-->3)beta-D-glucans, occurs upon loss of the multiple modes of glycosyl transfer to a single one.