Abstract
To understand the production of fructo- oligosaccharides in asparagus storage roots, the accumulation of exogenous carbohydrates and changes in the amount of short-chain fructo-oligosaccharides (degree of polymerization (DP) = 3 and 4) were examined in excised stem and root tissues of young asparagus plantlets that had been cultured on a carbohydrate-rich medium. Analyses of the carbohydrates and water content of cultured segments showed that exogenous carbohydrates from the medium gradually penetrated each tissue, regardless of the type of carbohydrate. Short-chain fructo-oligosaccharides accumulated in segments that had been cultured for more than 12 hr on a medium that contained glucose, fructose or sucrose but not mannitol or sorbitol. Furthermore, not only root tissue but also stem tissue synthesized short- chain fructo-oligosaccharides in vitro. No increase in starch occurred in any segments with or without a carbohydrate in the medium. Short-chain fructo-oligosaccharides in cultured tissues started to increase at a lower concentration of exogenous carbohydrate in root segments than in stem segments, accumulated to a greater level in the former than they did in the latter after 96 hr- of culture. The threshold level for fructo-oligosaccharide synthesis triggered by the accumulated fructose, glucose and sucrose may be lower in root tissue than in stem tissue, that accounts for the difference in fructo-oligosaccharide content between stems and storage roots of intact plantlets.
