EFFECT OF TUNICAMYCIN ON METABOLISM OF UNCONJUGATED N-GLYCANS IN RELATION TO REGULATION OF TOMATO FRUIT RIPENING

The unconjugated N-glycans (UNGs) Man(3)(Xyl)GlcNAc(Fuc)GlcNAc and Man (5)GlcNAc influence tomato (Lycopersicon esculentum cv 'Rutgers') frui t ripening at nanomolar concentrations. In addition, we have shown a d elaying effect on ripening of tomato pericarp discs by 10 ng per g fre sh weight Man(5)GlcNAc, one of 10 UNGs purified from mature green toma to pericarp. In the present study, oligomannosidic UNGs from tomato fr uit exhibited activity similar to Man(5)GlcNAc. However, complex UNGs isolated from tomato pericarp did not show the same inhibitory effect as Man(3)(Xyl)GlcNAc(Fuc)GlcNAc, a complex N-glycan not detected in to mato. The metabolism of UNGs was also studied by metabolic labelling w ith C-14-glucosamine, revealing that the amount of oligomannosidic and complex type UNGs may change inversely during ripening. Both C-14-lab elled UNGs disappeared after treatment with tunicamycin, an inhibitor of N-glycosylation. There was a correlation between the appearance of UNGs and recovery of ripening after tunicamycin treatment. Furthermore , application of 10 nM Man(5)GlcNAc with 40 mu M tunicamycin prevented the delaying effect of tunicamycin. Our results indicate that endogen ous unconjugated Man(5)GlcNAc may have a vital role in triggering and modulating tomato fruit ripening.