Storage proteins and cell wall mobilisation in seeds of Sesbania virgata (Cav.) Pers. (Leguminosae)

Abstract

The endosperm of seeds of Sesbania virgata (Cav.) Pers. accumulates galactomannan as a cell wall storage polysaccharide. It is hydrolysed by three enzymes, one of them being α-galactosidase. A great amount of protein bodies is found in the cytoplasm of endospermic cells, which are thought to play the major role as a nitrogen reserve in this seed. The present work aimed at understanding how the production of enzymes that degrade storage compounds is controlled. We performed experiments with addition of inhibitors of transcription (actinomycin-d and α-amanitin) and translation (cycloheximide) during and after germination. In order to follow the performance of storage mobilisation, we measured fresh mass, protein contents and α-galactosidase activity. All the inhibitors tested had little effect on seed germination and seedling development. Actinomycin-d and cycloheximide provoked a slight inhibition of the storage protein degradation and concomitantly lead to an elevation of the α-galactosidase activity. Although α-amanitin showed some effect on seedling development at latter stages, it presented the former effect and did not change galactomannan degradation performance. Our data suggest that some of the proteases may be synthesised de novo, whereas α-galactosidase seems to be present in the endosperm cells probably as an inactive polypeptide in the protein bodies, being probably activated by proteolysis when the latter organelle is disassembled. These evidences suggest the existence of a connection between storage proteins and carbohydrates mobilisation in seeds of S. virgata, which would play a role by assuring a balanced afflux of the carbon and nitrogen to the seedling development.