RESUMO - Entre os principais polissacarídeos de reserva em plantas estão o amido, os frutanos e os polissacarídeos de reserva de parede celular. Estes últimos ocorrem principalmente em sementes e podem ser classificados de acordo com suas estruturas químicas em mananos, xiloglucanos e galactanos. Apesar das diferenças marcantes nas estruturas químicas, os polímeros dos três grupos apresentam propriedades físico-químicas semelhantes. Eles possuem em comum a função de reserva, uma vez que são completamente degradados após a germinação da semente e seus produtos são utilizados como fontes de carbono e energia para o crescimento inicial das plântulas. Por outro lado, cada um deles apresenta funções secundárias tais como o controle da embebição e distribuição de água nos tecidos das sementes e o controle da expansão celular dos cotilédones. Na presente revisão, apresentamos uma atualização sobre as estruturas químicas, ocorrência e metabolismo desses polissacarídeos em sementes. São discutidos alguns pontos de controle de sua deposição e mobilização, bem como suas funções biológicas e papéis ecológicos. Estes aspectos são abordados com ênfase nos possíveis mecanismos evolutivos que levaram às alterações nas relações estrutura-função nas paredes celulares primárias de plantas superiores e ao surgimento das paredes de reserva. TERMOS ADICIONAIS PARA INDEXAÇÃO: Parede celular, polissacarídeos, reserva, sementes,

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    • "In the S. polyantha seeds, there was no difficulty observed for seed imbibition (Martins et al. 2011), seed germination was not observed after several chemical and mechanical tests to break the dormancy of seeds (Martins et al. 2012), and the embryo was not immature; however, there was a high amount of mannose in the endosperm walls. The mannans exhibit a high degree of intermolecular interactions and form crystals in the cell wall, which provides stiffness and reduces solubility (Buckeridge et al. 2000a). Thus, it is probable that the delayed seed germination in S. polyantha is associated with the seed endosperm cell walls. "
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    ABSTRACT: Smilax polyantha Grisebach is a species native to the Brazilian Cerrado biome and is known as sarsaparilla in folk medicine. Despite its popular use, little is known about the propagation of this species, which is still actively illegally exploited. The present study aims to analyse the seed ontogeny and perform endosperm chemical analyses in S. polyantha to elucidate the structural and chemical factors that could be associated with the low germination rates and structural organisation of the seed. The ovules are orthotropic and bitegmic, have short funicles, single collateral vascular bundles that end in the chalaza, and a hypostasis that is composed of chalazal and nucellar cells. The seed covering is non-multiplicative. In mature seeds, the cellularised endosperm has thick-walled cells, the embryo is small and the tegmen comprises two layers of periclinal elongated cells with a red-orange content, which are covered by a cuticle. Histochemical tests detected the presence of lipids, proteins and polysaccharides in the cellular content of mature seeds. Chemical analyses indicated 46.7% hemicellulose per total weight, 67.3% glucose, 30.7% mannose, 1.9% galactose and an absence of fucose, arabinose and rhamnose. In conclusion, the delayed seed germination in S. polyantha is associated with the seed endosperm cell walls.
    Full-text · Article · Jan 2012 · Australian Journal of Botany
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    • "The Angiosperms display different strategies for seedling establishment that include accumulation of different storage compounds in their seeds (Buckeridge et al., 2000c). These polymers, which can be proteins and carbohydrates, are mobilized during development and their products are used for several purposes such as energy generation and production of raw material for building cells and tissues (Buckeridge et al., 2004). "
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    ABSTRACT: Endospermic legumes are abundant in tropical forests and their establishment is closely related to the mobilization of cell-wall storage polysaccharides. Endosperm cells also store large numbers of protein bodies that play an important role as a nitrogen reserve in this seed. In this work, a systems approach was adopted to evaluate some of the changes in carbohydrates and hormones during the development of seedlings of the rain forest tree Sesbania virgata during the period of establishment. Seeds imbibed abscisic acid (ABA), glucose and sucrose in an atmosphere of ethylene, and the effects of these compounds on the protein contents, α-galactosidase activity and endogenous production of ABA and ethylene by the seeds were observed. The presence of exogenous ABA retarded the degradation of storage protein in the endosperm and decreased α-galactosidase activity in the same tissue during galactomannan degradation, suggesting that ABA represses enzyme action. On the other hand, exogenous ethylene increased α-galactosidase activity in both the endosperm and testa during galactomannan degradation, suggesting an inducing effect of this hormone on the hydrolytic enzymes. Furthermore, the detection of endogenous ABA and ethylene production during the period of storage mobilization and the changes observed in the production of these endogenous hormones in the presence of glucose and sucrose, suggested a correlation between the signalling pathway of these hormones and the sugars. These findings suggest that ABA, ethylene and sugars play a role in the control of the hydrolytic enzyme activities in seeds of S. virgata, controlling the process of storage degradation. This is thought to ensure a balanced flow of the carbon and nitrogen for seedling development.
    Full-text · Article · Oct 2010 · Annals of Botany
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