Abstract
Key messageDifferences in the composition and the structural organisation of the extracellular matrix correlate with the morphogenic competence of the callus tissue that originated from the isolated endosperm of kiwifruit.The chemical composition and structural organisation of the extracellular matrix, including the cell wall and the layer on its surface, may correspond with the morphogenic competence of a tissue. In the presented study, this relationship was found in the callus tissue that had been differentiated from the isolated endosperm of the kiwiberry, Actinidia arguta. The experimental system was based on callus samples of exactly the same age that had originated from an isolated endosperm but were cultured under controlled conditions promoting either an organogenic or a non-organogenic pathway. The analyses which were performed using bright field, fluorescence and scanning electron microscopy techniques showed significant differences between the two types of calli. The organogenic tissue was compact and the outer walls of the peripheral cells were covered with granular structures. The non-organogenic tissue was composed of loosely attached cells, which were connected via a net-like structure. The extracellular matrices from both the non- and organogenic tissues were abundant in pectic homogalacturonan and extensins (LM19, LM20, JIM11, JIM12 and JIM20 epitopes), but the epitopes that are characteristic for rhamnogalacturonan I (LM5 and LM6), hemicellulose (LM25) and the arabinogalactan protein (LM2) were detected only in the non-organogenic callus. Moreover, we report the epitopes, which presence is characteristic for the Actinidia endosperm (LM21 and LM25, heteromannan and xyloglucan) and for the endosperm-derived cells that undergo dedifferentiation (loss of LM21 and LM25; appearance or increase in the content of LM5, LM6, LM19, JIM11, JIM12, JIM20, JIM8 and JIM16 epitopes).
Highlights
Unorganised cell masses, which are called the callus can theoretically be produced from any living plant cell (Ikeuchi et al 2013 and references therein)
The experimental systems that were used in this study enabled to compare the cell wall composition and structures that cover the organogenic callus (OC) and non-organogenic callus (NOC) callus surface to determine whether the structural-chemical characteristic of an apoplast could indicate different morphogenic competences
Regardless of the OC extracellular matrix (ECM) that covered the surface of the explant, another type of ECM was observed in the vicinity of the endosperm cells and their derivatives (Fig. 8), in which epitopes belonging to the extensins (JIM11, JIM12 and JIM20) and hemicelluloses were detected
Summary
Unorganised cell masses, which are called the callus can theoretically be produced from any living plant cell (Ikeuchi et al 2013 and references therein). An increasing amount of literature data has indicated that all of these components are involved in the different developmental processes. It is postulated that pectins are involved in growth, morphogenesis, development, defence, cell adhesion and wall porosity, as well as ion or enzyme binding (reviewed in Mohnen 2008; Daher and Braybrook 2015). The arabinogalactan proteins (AGPs) are involved in cell differentiation, morphogenesis, plant defence and reproductive processes (for review see Showalter 2001). Some AGPs display a specific expression pattern during organ development or in an in vitro culture, where they diversify cells with different identities (Knox et al 1991; Konieczny et al 2007; Potocka et al 2018). May involve galactosyl residue(s) on RG backbones
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