Atividade indutora de fitoalexinas e produção de substancias fungitoxicas durante a germinação de sementes de Sesbania marginata Benth

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

Sesbania marginata Benth is a tropical legume that stores galactomannan in its thickened endospermic cell walls. These polysaccharides are composed of a linear backbone of 13-1,4- linked D-mannose residues to which D-galactose residues are attached by a-1,6 linkages. Following germination, the galactomannan is completely broken down producing considerable amounts of mono and oligosaccharides, which are transferred to the growing embryo. Concomitantly, phytoalexin-inducing molecules are produced and fungitoxic compounds are released from the germinating seeds. In the present work we investigated the possibility of some oligosaccharides generated during galactomanan degradation can induce phytoalexin production in soybean cotyledons - a test species used for assays of eliciting activity- and we extracted the fungitoxic compounds following germination. Extracts from endosperm+coat of 4-6 days of germination and from isolated endosperms of 1 and 5 days of germination were shown to be more effective in promoting phytoalexin production. Fractionation on Bio-Gel P2 column indicated that the active molecules found in some fractions are composed by two manosyl and one galactosyl residues, being a trissaccharide resultant of the galactomannan degradation. Fungitoxic compounds were extracted from seed exsudates and intact seeds after 48 h of germination. At least four fungitoxic substances were detected, some of them already present in quiescent seeds and other appearing after 1 day of germination. Our data suggest that besides playing a role in water imbibition and as a source of carbon for the embryo growth, galactomannans generate fragments that can signal plants to protect themselves by activating defense mechanisms in their tissues following germination. The release of these fragments and the presence of fungitoxic compounds in seeds of S. marginata seem to be closely related to their carbohydrate storage metabolism, allowing these seeds to germinate and the seedlings to develop in a highly competitive environment

ASSUNTO(S)

carboidratos sementes germinação

ACESSO AO ARTIGO

Documentos Relacionados