Distribution of some arabinogalactan protein epitopes during somatic embryogenesis and organogenesis on leaf explants on centaury (Centaurium erythraea Rafn)

Abstract

Arabinogalactan proteins (AGPs) are a family of ubiquitous hydroxyproline-rich glycoproteins present in plasma membranes, cell walls and secretions of plants. Since AGPs are highly glycosylated, more than 90% of their total molecular mass comes from carbohydrate moieties consisting of various arabinogalactosyl chains (AG sugar chains), which are thought to be important for thediverse functions of AGPs. AGPs are implicated in many aspects of plant growth and development, including cell differentiation, organogenesis and somatic embryogenesis (SE). The localization of AG sugar chains in plant tissues can be visualised using monoclonal antibodies (mAbs) that can detect different AGP epitopes. The aim of this study was to investigate changes in the localization of AGPs during induction of indirect SE and shoot organogenesis on leaf explants of centaury. Immunofluorescence labelling of leaf sections was performed with a set of mAbs (MAC207, JIM4, JIM8, JIM13, JIM15, LM2 and LM14). The results revealed that AGPs recognized by all mAbs tested were expressed in numerous meristematic cells from which somatic embryos develop. The AGP epitope recognised by the JIM4 antibody showed stronger intensity of immunofluorescence in the cell walls of protodermal cells of globular somatic embryos, whilst MAC207 and JIM13 epitopes were detected in cotyledonary somatic embryos. Strong immunofluorescence of the AGPs epitopes recognized with JIM4 and MAC207 mAbs were observed in the cells of apical meristem and leaf primordia of adventitious buds. These results suggest that AGPs play an important developmental role during formation of somatic embryos and adventitious buds from leaf explants of centaury.