Oligosaccharide Accumulation in Legume Seeds

Research project P 13955 Oligosaccaride Accumulation in Legume Seeds Andreas RICHTER 11.10.1999 Raffinose family oligosaccharides are major nonstructural carbohydrates in seeds of important grain legumes. These galactosyl-sucrose oligosaccharides contain alpha-galactosidic linkages, which are not digestible by humans, thereby reducing the nutritional benefits and acceptance of grain legumes. However, raffinose family oligosaccharides are believed to facilitate the acquisition of desiccation tolerance during maturation drying of plant seeds and are a source of carbon for the germinating seedling. As a consequence, breeding programs, which are designed at minimising the anti-nutritional characteristics of seeds by reducing the content of raffinose family oligosaccharides, should not dismiss their positive roles for the plant. However, little is known on the regulation of the accumulation of raffinose family oligosaccharides during seed development. The oligosaccharide content of mature seeds is highly variable, ranging from less than 2% of dry matter to more than 9%. Although the basic biosynthetic pathway of raffinose family oligosaccharides has been established almost two decades ago, recent research has indicated that our knowledge on the involved enzymes is yet incomplete, and that several alternative routes may exist in the biosynthesis of individual oligosaccharides. No metabolic model is currently available to explain the differences in seed oligosaccharide content in a physiological context. The ojective of this project is to understand the principles by which the accumulation of oligosaccharides in seeds is regulated. Towards this goal, the metabolism and developmental physiology of raffinose family oligosaccharides will be thoroughly characterized and comparatively assessed in legume genotypes which have been selected for extreme variation in their oligosaccharide content. This will allow us to identify key steps that are either blocked or upregulated. in individual genotypes. Thereby, the outcome of this project will provide a basis to investigate the molecular regulation of raffinose family oligosaccharides, and to critically test their physiolological significance in plant seeds.