The regulation and metabolism of raffinose family oligosaccharides in malting barley

• Main Author: Greenwood, Michelle
• Published: Heriot-Watt University 2007
• Subjects: 664
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486269

The raffinose family oligosaccharides (RFO) are alpha-galactosyl derivatives of sucrose, and the most common are raffinose, stachyose and verbascose. Raffinose is found exclusively in the embryo. Embryos and endosperms of barley (Hordeum vulgare. Cv. Golden Promise) were studied throughout their development and into maturity to investigate the 'relationships among a-amylase, carbohydrate, abscisic acid (ABA), raffinose synthesis pathway and the onset of desiccation tolerance. The onset of desiccation tolerance corresponds to an increase in starch, a-amylase, raffinose and a decrease in monosaccharides, stachyose and sucrose in the embryo of immature grains. A 5 fold increase was observed between 3-4 W.P.A of raffinose. 4-5 W.P.A, in the embryo a-galactosidase increases from 0.125 - 0.54 U/dry wt. The increase of raffinose precedes by a week the rise in a.:.galactosidase. In immature embryos, compared to the control without ABA, raffinose and galctose slightly increaSed and myo-inositol and glycerol decreased. ABA induced the down regulation of photochrome Band glutathione S-transferases. During imbition of mature grains in the embryo raffinose, melibiose and stachyose decreased to undetectable by 28, 17 and 17 h respectivlty however, sucrose increased. In the dormant samples metabolism fluctuated only slightly'. Galactose and raffinose was only present in dormant grain. Germination percentage was adversely influenced by salt and osmotic stress (PEG). Expression of raffinose synthase increased after 5 and 48 h of NaCI treatment and at 30°C during dehydration and re-hydration. The gene was also detected throughout 5 days of germination. In summary, water deficit stress caused pronounced effects on carbohydrate metabolism in barley embryos.RFO,s and glycerol were generally depressed by all stress treatments, which suggests RFO's may not playa direct role in inducing tolerance in embryo tissues.