Published for the Annals of Botany Co. by Academic Press
Annals of Botany vol:111 issue:3 pages:385-393
Background and aims The need is high to search for natural compounds with superior prebiotic, antioxidant and immunostimulatory properties for use in (food) applications. Raffinose Family Oligosaccharides (RFOs) show such properties. Moreover, they contribute to stress tolerance in plants acting as putative membrane stabilizers, antioxidants and signalling agents.
Methods A large scale soluble carbohydrate screening was performed within the plant kingdom. An unknown compound accumulated to a high extent in early spring red deadnettle (Lamium purpureum) but not in other RFO plants. The compound was purified and its structure was unravelled with NMR. Organs and organ parts of red deadnettle were carefully dissected and analysed on soluble sugars. Phloem sap content was analysed by a common EDTA-based method.
Key results Early spring red deadnettle stems and roots accumulate high concentrations of the reducing trisaccharide manninotriose (Galα1,6Galα1,6Glc), a derivative of the non-reducing RFO stachyose (Galα1,6Galα1,6Glcα1,2βFru). Detailed soluble carbohydrate analyses on dissected stem and leaf sections together with phloem sap analyses strongly suggest that stachyose is the main transport compound, but extensive hydrolysis of stachyose to manninotriose seems to occur along the transport path. Based on the specificities of the observed carbohydrate dynamics, the putative physiological roles of manninotriose in red deadnettle are discussed.
Conclusions Here it is demonstrated for the first time that manninotriose is a novel and important player in the RFO metabolism of red dead deadnettle. It is proposed that manninotriose represents a temporal storage carbohydrate in early spring deadnettle, at the same time perhaps functioning as a membrane protector and/or as an antioxidant in the vicinity of membranes as recently suggested for other RFOs and fructans. This novel finding urges further research on this peculiar carbohydrate on a broader array of RFO accumulators.