Arabinogalactan proteins and the extracellular matrix surface network during peach palm somatic embryogenesis

Somatic embryogenesis has been described in peach palm as a reliable method for its in vitro multiplication and conservation. In this study, we evaluated the possible role of arabinogalactan proteins (AGPs) during this morphogenetic pathway. The presence of Yariv reagent, a synthesized chemical antibody that specifically binds AGP molecules, affected somatic embryos and callus development rate, but no effect was observed on fresh weight increment. This substance also had profound effects on embryo morphology: somatic embryos presented loose cells in the protoderm and no signs of polarization could be observed. To better evaluate the role of AGPs, analyses of specific monoclonal antibodies (MAbs) against different AGP epitopes revealed a specific pattern of distribution for each epitope. MAb JIM13 had differential expression and showed intense signal on the embryogenic sector and some immediately adjacent layers. MAb JIM7 against pectin recognized cell walls and a specific layer over the developing somatic embryo, as well as over the shoot meristem region of mature somatic embryos. This corresponds to an extracellular matrix surface network (ECMSN) associated with the development of somatic embryos and closely related to the expression of MAb JIM13. Scanning electron microscopy confirmed the presence of an ECMSN covering a specific group of cells and ultra-structural analyses revealed that the ECMSN had lipophilic substances.