Rhizobium Lipooligosaccharides Rescue a Carrot Somatic Embryo Mutant.

At a nonpermissive temperature, somatic embryos of the temperature-sensitive (ts) carrot cell mutant ts11 only proceed beyond the globular embryo stage in the presence of medium conditioned by wild-type embryos. The causative component in the conditioned medium has previously been identified as a 32-kD acidic endochitinase. In search of a function for this enzyme in plant embryogenesis, several compounds that contain oligomers of N-acetylglucosamine were tested for their ability to promote ts11 embryo formation. Of these compounds, only the Rhizobium lipooligosaccharides or nodulation (Nod) factors were found to be effective in rescuing the formation of ts11 embryos. These results suggest that N-acetylglucosamine-containing lipooligosaccharides from bacterial origin can mimic the effect of the carrot endochitinase. This endochitinase may therefore be involved in the generation of plant analogs of the Rhizobium Nod factors.