Long-distance transport and metabolism of unconjugated N-glycans in tomatoplants

The long-distance transport of UNGs (unconjugated N-glycans) was studied in tomato plants. Radiolabelled N-glycans ( [C-14]-Man(5)GlcNAc and [H-3]-Man (5)GlcNAcol) were applied on the cut petiole of the first leaf of young tom ato plantlets, Radioactivity was measured in parts of the plant, showing th at both components are xylem-mobile, [H-3]-compounds accumulated mainly in the cotyledons whereas [C-14] was mainly found in the upper parts. The chem ical status of the proximal part of the glycan thus seemed to be of importa nce in their distribution in the plant. Transport by the phloem also occurr ed, but it remains unclear whether [3H]Man(5)GlcNAc-ol is transported as th e intact structure or as a degradation product, Chromatography studies show ed that [H-3]-Man(5)GlcNAc-ol began to be degraded after only 90 min of tra nsport and was completly degraded after 6 h. The degradation products could be identified as Man(4)-GlcNAc-ol, Man(3)-GlcNAc-ol and Man-GlcNAc-ol. The refore, the degradation was due to alpha-mannosidase activities which can a ct on N-glycan structures, hydrolysing alpha-linkages between two mannose r esidues. These results showed that metabolism and transport of UNGs are clo sely related in the tomato plant.