Arabinogalactan-protein and pectin epitopes in relation to an extracellular matrix surface network and somatic embryogenesis and callogenesis in Trifolium nigrescens Viv.

Abstract

The formation of an extracellular matrix surface network (ECMSN), and associated changes in the distribution of arabinogalactan-protein and pectin epitopes, have been studied during somatic embryogenesis (SE) and callogenesis of Trifolium nigrescens Viv. Scanning electron microscopy observations revealed the occurrence of an ECMSN on the surface of cotyledonary-staged somatic embryos as well as on the peripheral, non-regenerating callus cells. The occurrence of six AGP (JIM4, JIM8, JIM13, JIM16, LM2, MAC207) and four pectin (JIM5, JIM7, LM5, LM6) epitopes was analysed during early stages of SE, in cotyledonary-staged somatic embryos and in non-embryogenic callus using monoclonal antibodies. The JIM5 low methyl-esterified homogalacturonan (HG) epitope localized to ECMSN on the callus surface but none of the epitopes studied were found to localize to ECMSN over mature somatic embryos. The LM2 AGP epitope was detected during the development of somatic embryos and was also observed in the cell walls of meristematic cells from which SE was initiated. The pectic epitopes JIM5, JIM7, LM5 and LM6 were temporally regulated during SE. The LM6 arabinan epitope, carried by side chains of rhamnogalacturonan-I (RG-I), was detected predominantly in cells of embryogenic swellings, whilst the LM5 galactan epitope of RG-I was uniformly distributed throughout the ground tissue of cotyledonary-staged embryoids but not detected at the early stages of SE. Differences in the distribution patterns of low and high methyl-esterified HG were detected: low ester HG (JIM5 epitope) was most abundant during the early steps of embryo formation and highly methyl-esterified form of HG (JIM7 epitope) became prevalent during embryoid maturation.

Imaging of native early embryogenic tissue of Scots pine (Pinus sylvestris L.) by ESEM

“…The surfaces of the bottle shape cells as well as the embryonal heads were covered with mucilaginous matrix -ECM (ECMSN). It seems that consistency of this matrix is different from the networklike or fibrillar structure observed in other species [4,17,18]. Consistent with Lai et al [4] we suppose that the ECM layer forms bridges connecting the neighboring cells together and may be the early structural marker for embryogenic tissues.…”

Arabinogalactan proteins improve plant regeneration in barley (Hordeum vulgare L.) anther culture

“…The mechanism by which AGPs affects embryo development remains unclear. However, specific localization of some AGPs epitopes on embryogenic cells (Chapman et al 2000) as well as on embryo structures (Pilarska et al 2013) suggest the involvement of these proteins in the induction and maintenance of cell polarity. Indeed, a majority of barley embryos obtained in the presence of gum arabic were bipolar and displayed all structures typical for zygotic embryos, such as scutellum, coleoptile and coleorhiza.…”

“…Anthers from spikes before and after the pretreatment step as well as the explants after 3, 5, 7, 10, 14, 21 and 28 days of culture on media with or without 10 mg l −1 gum arabic were fixed and embedded as described by Pilarska et al (2013). Sections (5 µm thick) were stained with 0.1% water solution of toluidine blue (Sigma, Germany) and observed under a light microscope.…”

Extracellular matrix surface network is associated with non-morphogenic calli of Helianthus tuberosus cv. Albik produced from various explants

“…However, in the present studies, in spite of the occurrence of ECMSN the calli were not morphogenetic. The extracellular layer covering callus cells, which is not involved in the regeneration process, has previously been reported during androgenesis in wheat [34], somatic embryogenesis in banana [35] and clover cultures [36]. The role of ECMSN cannot be generalized but it is evident that it is formed on the surface of cultured in vitro tissues regardless of its morphogenetic competence.…”