Search

Xyloglucans in the non-lignified primary cell walls of different species of monocotyledons have diverse structures, with widely varying proportions of oligosaccharide units that contain fucosylated side chains (F side chains). To determine whether fucosylated xyloglucans occur in all non-lignified walls in a range of monocotyledon species, we used immunofluorescence microscopy with the monoclonal antibody CCRC-M1. The epitope of this antibody, α-L-Fucp-(1→2)-β-D-Galp, occurs in F side chains. In most non-commelinid monocotyledons, the epitope was found in all non-lignified walls. A similar distribution was found in the palm Phoenix canariensis, which is a member of the basal commelinid order Arecales. However, in the other commelinid orders Zingiberales, Commelinales, and Poales, the occurrence of the epitope was restricted, sometimes occurring in only the phloem walls, but often also in walls of other cell types including stomatal guard and subsidiary cells and raphide idioblasts. No epitope was found in the walls of the commelinids Tradescantia virginiana (Commelinaceae, Commelinales) and Zea mays (Poaceae, Poales), but it occurred in the phloem walls of two other Poaceae species, Lolium multiflorum and L. perenne. The distribution of the epitope is discussed in relation to xyloglucan structures in the different taxa. However, the functional significance of the restricted distributions is unknown. [ABSTRACT FROM PUBLISHER]

Except in the Poaceae, little is known about the structures of the xyloglucans in the primary walls of monocotyledons. Xyloglucan structures in a range of monocotyledon species were examined. Wall preparations were isolated, extracted with 6 M sodium hydroxide, and the extracts treated with a xyloglucan-specific endo-(1 → 4)-β-glucanase preparation. The oligosaccharides released were analyzed by high-performance anion-exchange chromatography and by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry. Oligosaccharide profiles of the non-commelinid monocotyledons were similar to those of most eudicotyledons, indicating the xyloglucans were fucogalactoxyloglucans, with a XXXG a core motif and the fucosylated units XXFG and XLFG. An exception was Lemna minor (Araceae), which yielded no fucosylated oligosaccharides and had both XXXG and XXGn core motifs. Except for the Arecales (palms) and the Dasypogonaceae, which had fucogalactoxyloglucans, the xyloglucans of the commelinid monocotyledons were structurally different. The Zingiberales and Commelinales had xyloglucans with both XXGn and XXXG core motifs; small proportions of XXFG units, but no XLFG units, were present. In the Poales, the Poaceae had xyloglucans with a XXGn core motif and no fucosylated units. In the other Poales families, some had both XXXG and XXGn core motifs, others had only XXXG; XXFG units were present, but XLFG units were not. [ABSTRACT FROM PUBLISHER]

The molecular ordering of cellulose, including its crystallinity, in the unlignified primary cell walls of three monocotyledons (Italian ryegrass, pineapple, and onion) and one dicotyledon (cabbage) was characterized by solid-state 13C NMR spectroscopy. These species were chosen because their primary cell walls have different non-cellulosic polysaccharides and this may affect the molecular ordering of cellulose. Values of the proton rotating-frame relaxation [T1p(H)] and spin-spin relaxation [T2(H)] time constants showed that the cellulose in the cell walls of all four species was in a crystalline rather than an amorphous state. Furthermore, a resolution enhancement procedure showed that the triclinic (Iα) and the monoclinic (Irβ) crystal forms of cellulose were present in similar proportions in these cell walls. However, the calculated cross-sectional dimensions of the cellulose crystallites varied among the cell walls (in the range 2–3 nm): the largest were in the Italian ryegrass, the smallest were in the onion and cabbage, and those of intermediate size were in the pineapple. The crystallite dimensions may thus be affected by the non-cellulosic polysaccha-ride compositions of the cell walls. [ABSTRACT FROM AUTHOR]

The molecular mobility of the non-cellulosic polysaccharides in hydrated primary cell walls of three monocotyledons (Italian ryegrass, pineapple and onion) and one dicotyledon (cabbage) was studied using solid-state 13C NMR spectroscopy. These cell walls were chosen as they have different non-cellulosic polysaccharide compositions. By exploiting proton rotating-frame and spin-spin relaxation time constants three different cell wall domains which responded to cross-polarization experiments were identified. Most of the non-cellulosic polysaccharides occupied a mobile domain (C), but some occupied a partly rigid domain (B). Crystalline cellulose occupied a highly rigid domain (A). In the cell walls of Italian ryegrass and pineapple, domain C contained mainly glucuronoarabinoxylans and small amounts of rhamnogalacturonans; domain B contained small amounts of xyloglucans and galacturonans. However, in the cell walls of onion and cabbage, domain C contained mainly rhamnogalacturonans with galactans (in onion) or arabinans (in cabbage) as side chains; domain B contained galacturonans and xyloglucans. Single-pulse excitation was used on Italian ryegrass and cabbage cell walls to reveal signals from a highly mobile fourth domain (D). In Italian ryegrass cell walls domain D contained glucuronoarabinoxylans and small amounts of rhamnogalacturonan, whereas in cabbage cell walls it contained arabinan side chains of rhamnogalacturonans. A novel feature of the research was the use of solid-state 13C NMR spectroscopy to examine the molecular mobilities of the polysaccharides in monocotyledon cell walls that contain glucuronoarabinoxylans. [ABSTRACT FROM AUTHOR]

Suggests cautions in attributing characteristics of the grasses to monocotyledons as a whole. Results of phylogenetic analysis based upon the chloroplast gene sequences of the monocotyledon families; Differences on the analyses of the primary cell wall of monocotyledons and dicotyledons.