In plant embryogenesis, inductive interactions mediated by diffusable signal molecules are most likely of great importance. Evidence has been presented that at late globular stages in plant embryogenesis, perturbation of the polar auxin transport results in abberrant embryo morphology. Rhizobium lipooligosaccharides or Nod factors are a newly discovered class of bacterial molecules that are able to trigger initial steps in root nodule development in legumes. Part of the activity of Nod factors may be directed towards alteration of endogenous plant growth regulator balance. The same bacterial Nod factors promoted the formation of globular embryos in the carrot cell line ts11. Whether there exist plant analogues of the Nod factors and whether these molecules are active as a more universal control system perhaps designed to initiate and or mediate gradients in auxin and cytokinin remains to be determined.