Evidence for somatic embryogenesis during plant regeneration from seedling-derived callus of dodder (Cuscuta trifolii Bab. et Gibs).

In this paper comparative histological studies of embryo-like structures originating from callus cultures, and zygotic embryos originating from sexual seeds of Cuscuta trifolii are reported. The embryos of somatic cell and zygote origin showed similar morphological and anatomical features, such as a complete lack of cotyledon development and the differentiation of a developmentally unique root primordium specialised for water storage. Based on these findings, the regeneration of C. trifolii from callus cultures is shown to proceed along the pathway of somatic embryogenesis.

Lipo-oligosaccharides of Rhizobium induce infection-related early nodulin gene expression in pea root hairs.

This paper shows that lipo-oligosaccharides (Nod factors) synthesized by Rhizobium bacteria elicit the induction of infection-related early nodulin genes (PsENOD5 and PsENOD12) in pea root hairs. R. leguminosarum bv. viciae secretes a mixture of Nod factors containing a C18 fatty acid chain with 4 (C18:4) or 1 double bond (C18:1). Purified Nod factors harbouring either a C18:4 or a C18:1 acyl moiety induce the expression of the pea early nodulin genes, PsENOD5 and PsENOD12, but the kinetics of induction are different. The expression of both early nodulin genes is induced in a transient manner by the purified Nod factors while a mixture of the Nod factors extends the period during which these genes are expressed. In spite of the host-specific nature of the infection process, heterologous Nod factors of R. meliloti also induce the expression of PsENOD5 and PsENOD12 genes, though with a marked delay compared with the homologous compounds.