Embryogenic cultures of Norway spruce (Piceaabies) are composed of pro-embryogenic masses (PEMs) andsomatic embryos of various developmental stages. Auxin is important forPEM formation and proliferation. In this report we show that depletionof auxin blocks PEM development and causes large-scale cell death.Extracts of the media conditioned by embryogenic cultures stimulatedevelopment of PEM aggregates in auxin-deficient cultures. Partialcharacterization of the conditioning factor shows that it is alipophilic, low-molecular-weight molecule, which is sensitive tochitinase and contains GlcNAc residues. On the basis of thisinformation, we propose that the factor is a lipophilic chitinoligosaccharide (LCO). The amount of LCO correlates to thedevelopmental stages of PEMs and embryos, with the highest level in themedia conditioned by developmentally blocked cultures. LCO is notpresent in nonembryogenic cultures. Cell death, induced by withdrawalof auxin, is suppressed by extra supply of endogenous LCO or Nod factorfrom Rhizobium sp. NGR234. The effect can be mimicked bya chitotetraose or chitinase from Streptomyces griseus.Taken together, our data suggest that endogenous LCO acts as a signalmolecule stimulating PEM and early embryo development in Norwayspruce.
展开▼
