Cell Wall Architecture of the Elongating Maize Coleoptile

Abstract

The primary walls of grasses are composed of cellulose microfibrils, glucuronoarabinoxylans (GAXs), and mixed-linkage ␤-glucans, together with smaller amounts of xyloglucans, glucomannans, pectins, and a network of polyphenolic substances. Chemical imaging by Fourier transform infrared microspectroscopy revealed large differences in the distributions of many chemical species between different tissues of the maize (Zea mays) coleoptile. This was confirmed by chemical analyses of isolated outer epidermal tissues compared with mesophyll-enriched preparations. Glucomannans and esterified uronic acids were more abundant in the epidermis, whereas ␤-glucans were more abundant in the mesophyll cells. The localization of ␤-glucan was confirmed by immunocytochemistry in the electron microscope and quantitative biochemical assays. We used field emission scanning electron microscopy, infrared microspectroscopy, and biochemical characterization of sequentially extracted polymers to further characterize the cell wall architecture of the epidermis. Oxidation of the phenolic network followed by dilute NaOH extraction widened the pores of the wall substantially and permitted observation by scanning electron microscopy of up to six distinct microfibrillar lamellae. Sequential chemical extraction of specific polysaccharides together with enzymic digestion of ␤-glucans allowed us to distinguish two distinct domains in the grass primary wall. First, a ␤-glucan-enriched domain, coextensive with GAXs of low degrees of arabinosyl substitution and glucomannans, is tightly associated around microfibrils. Second, a GAX that is more highly substituted with arabinosyl residues and additional glucomannan provides an interstitial domain that interconnects the ␤-glucan-coated microfibrils. Implications for current models that attempt to explain the biochemical and biophysical mechanism of wall loosening during cell growth are discussed.Biochemical studies have provided a reasonably complete catalog of the major polysaccharides and phenolic substances that constitute the primary cell walls of angiosperms (McCann and Roberts, 1991;Carpita and Gibeaut, 1993). The walls of grasses and related monocots (commelinoids) have quite different compositions compared with those of all dicots and of the non-commelinoid monocot species (Carpita, 1996). The "type II" cell walls of commelinoid monocots are characterized by cellulose microfibrils cross-linked by glucuronoarabinoxylans (GAXs) and a network of polyphenolic substances (Carpita and Gibeaut, 1993;Carpita, 1996). Maize (Zea mays) and other members of the Poales also contain developmentally regulated polymers, the mixed-linkage (133),(134)-␤-dglucans (hereafter, called ␤-glucans). The ␤-glucans are initially absent from meristematic cells but accumulate up to about 20% dry mass of the cell wall coincident with the most rapid rates of coleoptile elongation (Kim et al., 2000). As the elongation rate slows, the ␤-glucan is hydrolyzed by exo-and endo-␤-d-glucanases located in the wall. Concomitant with th...

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Generally, xylan is the most closely associated polysaccharide to lignin, and NMR studies have also clearly identified lignin-glucuronic acid ester bonds (Yuan et al, 2011). Also, MLGs closely coat low-substituted xylan regions, likely via non-covalent interactions (Carpita et al, 2001;Kozlova et al, 2014). Furthermore, some components can also affect the distribution of other components.…”

The use of FTIR spectroscopy to monitor modifications in plant cell wall architecture caused by cellulose biosynthesis inhibitors

“…The analysis of loading factors can be used to identify the molecular factors that underlie the grouping or for discrimination of the original data. 6 The use of PCA in conjunction with FTIR spectroscopy has proved to be an important tool in the study of cell wall structure and composition heterogeneity in a species, 7,8 or among different species, 5,9-11 as well as in the identification and classification of mutants with altered cell wall compositions. 6,[12][13][14] This approach has been also very useful in the characterization of the modifications appearing in this kind of mutants [15][16][17][18][19][20] or in transgenic plants with altered cell walls 21 and in the modifications to cell wall composition induced by different biotic or abiotic stress factors.…”

The Spatially Variable Inhibition by Water Deficit of Maize Root Growth Correlates with Altered Profiles of Proton Flux and Cell Wall pH

“…Bacon et al, 1998;Sharp, 2002), and (4) cell wallstructural changes (e.g. Wu et al, 1996;Carpita et al, 2001;Takeda et al, 2002;Fry, 2004) and genetic changes (e.g. Wagner and Kohorn, 2001;Foreman et al, 2003).…”