CARBON STARVATION INCREASES ENDOGLYCOSIDASE ACTIVITIES AND PRODUCTIONOF UNCONJUGATED N-GLYCANS IN SILENE ALBA CELL-SUSPENSION CULTURES

We previously reported the occurrence of oligomannosides and xylomanno sides corresponding to unconjugated N-glycans (UNGs) in the medium of a white campion (Silene alba) cell suspension. Attention has been focu sed on these oligosaccharides since it was shown that they confer biol ogical activities in plants. In an attempt to elucidate the origin of these oligosaccharides, we studied two endoglycosidase activities, put ative enzymes involved in their formation. The previously described pe ptide-N-4-(N-acetyl-glucosaminyl) asparagine amidase activity and the endo-N-acetyl-beta-D-glucosaminidase activity described in this paper were both quantified in white campion cells during the culture cycle w ith variable initial concentrations of sucrose. The lower the sucrose supply, the higher the two activities. Furthermore, endoglycosidase ac tivities were greatly enhanced after the disappearance of sugar from t he medium. The production of UNGs in the culture medium rose correlati vely. These data strongly suggest that the production of UNGs in our w hite campion cell-suspension system is due to the increase of these en doglycosidase activities, which reach their highest levels of activity during conditions of carbon starvation.