Unconjugated Man5GlcNAc Occurs in Vegetative Tissues of Tomato

Unconjugated Man alpha 1-->6(Man alpha 1-->3)Man alpha 1-->6(Man alpha 1-->3)Man beta 1-->4GlcNAc (Man5Glc NAc) delayed ripening when added exogenously at 10 ng g-1 fr. wt to both whole tomato fruit and excised pericarp tissue discs. In addition, Man5GlcNAc was one of 10 unconjugated N-glycans purified from tomato pericarp tissue. When applied exogenously at a concentration of 10 nM, Man5GlcNAc prevented the delay of ripening induced by tunicamycin, an inhibitor of its de novo synthesis. Since it was possible that this unconjugated N-glycan might be specifically related to ripening, we checked to see if it also occurred in fully expanded leaf and stem tissues using high-pH anion-exchange chromatography with pulsed amperometric detection. This method allowed us to detect 1 ng of oligosaccharide and to quantify accurately amounts in the range 60-600 ng per injection, significantly more sensitive than the amine-bonded HPLC method previously used to separate and quantify unconjugated N-glycans in tomato fruit pericarp tissue. Four high-mannosyl type unconjugated N-glycans were detected in tomato vegetative tissues, including Man5GlcNAc. These results support a potential role of Man5GlcNAc and/or other unconjugated N-glycans in plant developmental processes, in addition to its apparent role as a modulator of senescence of fruit. However, an initial experiment showed no effect of Man5GlcNAc on senescence of tomato leaf discs, as measured by chlorophyll loss.