Rhamnogalacturonan I in Solanum tuberosum tubers contains complex arabinogalactan structures

Abstract

A rhamnogalacturonan I polysaccharide was isolated from potato ( Solanum tuberosum cv. Posmo) tuber cell walls and characterised by enzymatic digestion with an endo-β-1 → 4-galactanase and an endo-α-1 → 5-arabinanase, individually or in combination. The reaction products were separated using size-exclusion chromatography and further analysed for monosaccharide composition and presence of epitopes using the LM5 anti-β-1 → 4-galactan and LM6 anti-α-1 → 5-arabinan monoclonal antibodies. The analyses point to distinct structural features of potato tuber rhamnogalacturonan I, such as the abundance of β-1 → 4-galactan side chains that are poorly substituted with short arabinose-containing side chains, the presence of α-1 → 5-arabinan side chains substituted with β-1 → 4-galactan oligomers (degree of polymerisation >4), and the presence of α-1 → 5-arabinans that resist enzymatic degradation. A synergy between the enzymes was observed towards the degradation of arabinans but not towards the degradation of galactans. The effect of the enzymes on isolated RG I is discussed in relation to documented effects of enzymes heterologously expressed in potato tubers. In addition, a novel and rapid method for the determination of the monosaccharide and uronic acid composition of cell wall polysaccharides using high-performance anion exchange chromatography with pulsed amperometric detection is described.