Plant regeneration in leaf culture of Centaurium erythraea Rafn. Part 2: the role of arabinogalactan proteins

Arabinogalactan proteins (AGPs) are cell wall hydroxyproline-rich glycoproteins with diverse functions in plant growth and development. In this work the role of AGPs was comparatively studied in four developmental pathways that can be induced from centaury leaf explants-indirect somatic embryogenesis (ISE), indirect and direct shoot development (ISD and DSD) and direct root development (DRD). The addition of beta-d-glucosyl Yariv (beta GlcY) reagent, a synthetic phenylglycoside that specifically crosslinks AGPs, to the growth medium reduced the number of somatic embryos and adventitious buds formed per explant. The morphogenetic paths can be arranged in order of increasing sensitivity to beta GlcY as: DRD (insensitive) < ISD < DSD a parts per thousand(a) ISE. The content of AGPs increased during all processes, but the accumulation of AGPs was the most rapid during ISE and when ISE and ISD occurred simultaneously. We have identified four centaury AGP transcripts, CeAGP1-CeAGP4, of which CeAGP1, 2 and 4 code for fasciclin-like AGPs. CeAGP3 is an AG peptide with conserved DUF1070 domain. Expression pattern of these genes indicated specific involvement of CeAGP1 in ISE and unspecific involvement of CeAGP3 in morphogenesis.