H. Yunovitz et Kc. Gross, EFFECT OF TUNICAMYCIN ON METABOLISM OF UNCONJUGATED N-GLYCANS IN RELATION TO REGULATION OF TOMATO FRUIT RIPENING, Phytochemistry, 37(3), 1994, pp. 663-668
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.