Arabinogalactan-proteins containing uronic acids are essential molecules for growth processes in planta

Abstract

Arabinogalactans/arabinogalactan-proteins (AGPs) from different Poaceae are known to have an allergy protective effect in vivo [1]. But for the plants themselves, they are even more essential. They are important for growth of plant tissue and involved in complex processes like the induction of embryogenesis in microspore culture [2]. AGP, isolated by double precipitation with β-glucosyl Yariv reagent from whole grain of oat (Avena sativa L.), consists of a large carbohydrate moiety that is rich in galactose (63.0% (w/w)) and arabinose (32.8% (w/w)) and free of uronic acids. The carbohydrate part is composed of a 1,3-Galp backbone and is linked in position 6 to short 1,6-Galp side chains, terminating in Araf residues. In the protein part, high amounts of alanine, hydroxyproline and serine are found, which is typical for AGPs. The molecular mass of AGP was determined to be 83 kDa [3]. In contrast, AGPs isolated from leaves and seedlings of oat have appreciable amounts of uronic acids. These charged molecules as parts of AGPs are supposed to play an essential role during growth processes in the plant tissue [4]. AGP in grains, lacking traceable amounts of uronic acids, indicate the dormant state of this tissue.