Wall Ingrowths in Epidermal Transfer Cells of Vicia faba Cotyledons are Modified Primary Walls Marked by Localized Accumulations of Arabinogalactan Proteins

Abstract

Despite the importance of transfer cells in enhancing nutrient transport in plants, little is known about how deposition of the complex morphology of their wall ingrowths is regulated. We probed thin sections of mature cotyledon epidermal transfer cells of Vicia faba with affinity probes and antibodies specific to polysaccharides and glycoproteins, to determine the distribution of these components in their walls. Walls of these transfer cells consist of the pre-existing primary wall, a uniformly deposited wall layer and wall ingrowths which are comprised of two regions; an electron-opaque inner region and an electron-translucent outer region. The primary wall reacted strongly with antibodies against esterified pectin, xyloglucan, the side chains of rhamnogalaturonan-1 and a cellulase-gold affinity probe. The electron-opaque inner region of wall ingrowths displayed a similar labeling pattern to that of the primary wall, showing strong cross-reactivity with all antibodies tested, except those reacting against highly de-esterified pectins. The electron-opaque outer layer of developmentally more mature wall ingrowths reacted strongly with anti-callose monoclonal and polyclonal antibodies, but showed no reaction for pectin or xyloglucan antibodies or the cellulase-gold affinity probe. The plasma membrane-wall interface was labeled strongly with anti-arabinogalactan protein (AGP) antibodies, with some AGP-reactive antibodies also labeling the electron-translucent zone. Nascent wall ingrowths were labeled specifically with AGPs but not anti-callose. A reduction in wall ingrowth density was observed when developing transfer cells were exposed to beta-d-glucosyl Yariv reagent compared with controls. Our results indicate that wall ingrowths of transfer cells are primary wall-like in composition and probably require AGPs for localized deposition.

Miniature1-Encoded Cell Wall Invertase Is Essential for Assembly and Function of Wall-in-Growth in the Maize Endosperm Transfer Cell

“…Chourey, unpublished data). Although no biochemical data are available on the composition of maize WIGs, histochemical and biochemical analyses of transfer cells in V. faba cotyledons demonstrated that they are rich in cell wall polysaccharides and glycoproteins that are also found in the primary cell wall (Vaughn et al, 2007). Assuming that WIG in the maize BETC consists mainly of polysaccharides and glycoproteins, the stunted growth of mn1 WIGs may result from the lack of monosaccharides for polysaccharide biosynthesis, glycosylation, and numerous other metabolic and signaling functions.…”

“…Vaughn et al (2007) demonstrated that WIGs in the Vicia faba epidermal transfer cells are rich in cellulose, hemicellulose, pectin, callose, and arabinogalactan proteins, similar to the primary cell wall. Although transfer cells in developing seeds are described in a large number of plant species (Thompson et al, 2001), the most elaborate cellular morphology as well as extensive support for their possible roles in the metabolic and developmental biology of endosperm have been reported in 1 This work was supported by the start-up fund from the Department of Microbiology and Cell Science, University of Florida (to B.-H.K.…”

“…Transfer cells are ubiquitous among plants and are most often located at the aposymplastic junctions between maternal and filial generations of developing seeds (Offler et al, 2003;Vaughn et al, 2007). Vaughn et al (2007) demonstrated that WIGs in the Vicia faba epidermal transfer cells are rich in cellulose, hemicellulose, pectin, callose, and arabinogalactan proteins, similar to the primary cell wall.…”

Heteroblastic Development of Transfer Cells Is Controlled by the microRNA miR156/SPL Module

“…This transport capacity is conferred by wall protuberances that extend into the cell lumen, hence called wall "ingrowths". These ingrowths, considered to be primary wall-like in composition (Vaughn et al, 2007), are deposited secondarily on the inner face of the primary cell wall and function to enhance the area of surrounding plasma membrane, therefore increasing surface-to-volume ratio of the TC and consequently promoting potential transmembrane flux of solutes (Gunning et al, 1968;Gunning and Pate, 1974;Offler et al, 2003).…”

Ultrastructural Immunolocalization of Arabinogalactan Protein, Pectin and Hemicellulose Epitopes Through Anther Development inBrassica napus

“…AGPs may be attached to the plasma membranes via a glycosylphosphatidylinositol (GPI) lipid anchor, or may be part of the cell walls or of plant secretions (Seifert and Roberts 2007). In cell walls, AGPs have been implicated in different processes related to cell plate formation (Shibaya and Sugawara 2009), the coordination of cell wall assembly (Roy et al 1998;Vaughn et al 2007), the maintenance of the solubility of wall polymers prior to being incorporated into the cell wall (Carpita and Gibeaut 1993), or wall plasticity against desiccation (Moore et al 2013). Aside of their specific role in the cell wall, AGPs have been involved in a myriad of processes related to cell growth, development and reproduction, both in vivo and in vitro.…”