Characterization of the carbohydrate moiety of arabinogalactan-proteins from Avena sativa L., Secale cereale L. and Triticum aestivum L., isolated with Yariv reagent

The nonstarch polysaccharides, although minor constituents in common oat (Avena sativa L.), rye (Secale cereale L) and wheat (Triticum aestivum L.), are important for growth of plant tissue. Arabinogalactan-proteins (AGPs) from wheat induce embryogenesis in microspore culture [1] and play a role in breadmaking [2]. Already in 1975 [3], it has been claimed that in contrast to most other AGPs, those of Avena sativa L. and Triticum aestivum L. show no precipitation with Yariv reagent. Therefore, up to now it is common praxis to isolate AGPs from cereals by stepwise ethanol precipitation. This includes the disadvantage of contamination of AGP-preparations with other polysaccharides. Our investigations show for the first time that AGPs from Avena sativa L., Secale cereale L. and Triticum aestivum L. can be isolated by precipitation with β-glucosyl Yariv reagent after extraction with water, starch removal by centrifugation, protein denaturation and dialysis. Specific interaction of the isolated AGPs with Yariv could also be demonstrated by a gel-diffusion test. In size-exclusion-chromatography the isolated AGPs elute as individual peaks with a molecular mass specific for poacean AGP. Methylation analysis was performed to characterize the carbohydrate moiety of the AGP which mainly consists of 1-Araf, 1,3-Galp and 1,3,6-Galp.

References: [1] Letarte J et al. (2006) Plant Cell Reports 25(8):877. [2] Schrøder M et al. (1999) J.Agric. Food Chem. 48: 1334–1343. [3] Jermyn M, Yeow Y (1975) Aust. J. Plant Physiol. 2: 501–531.