1040-2519/96/0601-0445$08.00445Annu. Rev. Plant Physiol. Plant Mol. Biol. 1996. 47:445–76Copyright © 1996 by Annual Reviews Inc. All rights reservedSTRUCTURE AND BIOGENESIS OFTHE CELL WALLS OF GRASSESNicholas C. CarpitaDepartment of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana47907KEY WORDS: cereals, grasses, cell-wall polysaccharides, cell-wall biosynthesis, cell-wall ar-chitectureABSTRACTThe chemical structures of the primary cell walls of the grasses and their pro-genitors differ from those of all other flowering plant species. They vary in thecomplex glycans that interlace and cross-link the cellulose microfibrils to formastrongframework,inthe nature ofthe gel matrixsurrounding this framework,and in the types of aromatic substances and structural proteins that covalentlycross-link the primary and secondary walls and lock cells into shape. This re-view focuses on the chemistry of the unique polysaccharides, aromatic sub-stances, and proteins of the grasses and how these structural elements are syn-thesized and assembled into dynamic and functional cell walls. Despite widedifferences in wall composition, the developmental physiology of grasses issimilar to that of all flowering plants. Grass cells respond similarly to environ-mental cues and growth regulators, exhibit the same alterations in physicalproperties of the wall to allow cell growth, and possess similar patterns of wallbiogenesis during the development of specific cell and tissue types. Possibleunifying mechanisms of growth are suggested to explain how grasses performthe same wall functions as other plants but with different constituents and ar-chitecture.CONTENTSINTRODUCTION ......................................... .......................................................................... 446THE STRUCTURAL ELEMENTS OF THE PRIMARY WALLS OF THE POACEAE ...... 447Cellulose .................................................. .......................................................................... 447Glucuronoarabinoxylans ......................... .......................................................................... 447The (1→3),(1→4)-β-D-glucans................ .......................................................................... 448Annu. Rev. Plant. Physiol. Plant. Mol. Biol. 1996.47:445-476. Downloaded from arjournals.annualreviews.orgby University of Georgia on 04/26/06. For personal use only.Xyloglucan ............................................... .......................................................................... 450Other Glycans.......................................... .......................................................................... 450Pectic Substances..................................... .......................................................................... 450Aromatic Substances................................ .......................................................................... 451Structural Proteins................................... .......................................................................... 453Other Cell-Wall Substances..................... .......................................................................... 454CELL-WALL COMPOSITION AS A TAXONOMIC CHARACTER IN THEMONOCOTYLEDONAE..................... ..........................................................................454ARCHITECTURE......................................... ..........................................................................458STRUCTURAL DYNAMICS DURING CELL ELONGATION ...........................................462CELL-WALL BIOGENESIS IN GRASSES. .......................................................................... 465Biosynthesis of (1→3),(1→4)-ß-D-Glucan ......................................................................... 466Biosynthesis of Other Cell-Wall Polysaccharides.............................................................. 467GENETIC MODELS OF CELL-WALL DEVELOPMENT IN THE GRASSES................... 467INTRODUCTIONIn the early 1900s, Walter Norman Haworth and Edmund Langley Hirst,founding fathers of modern carbohydrate chemistry, began studies of thepentose constituents of cell walls of plants. Armed with only rudimentaryanalytical techniques, they and their colleagues defined the cell walls of es-parto grass as composed largely of (1→4)-β-D-xylans (58). By 1970, gaschromatography–mass spectrometry (GC-MS) was employed routinely forunequivocal determination of linkage structure of complex cell-wall polysac-charides. Techniques such as1H- and13C-nuclear magnetic resonance(NMR) spectroscopy provided anomeric configurations, linkage structures,and some three-dimensional configurations. Sequence-dependent endoglyca-nases were used to cleave polysaccharides into oligosaccharides that could becompletely sequenced. From characteristic repeating unit structures, the se-quence and conformation of very large polymers were deduced (20). By suchanalyses, the major polysaccharides of the walls of a wide range of floweringplants were defined, and the first models of how cell walls are put togetheremerged. In subsequent years, the dynamic interactions of individual compo-nents were reflected in more current models of the architecture of the primarycell wall of flowering plants—a strong framework of cellulose microfibrilsintertwined with xyloglucans that is embedded in a gel of uronic-acid-richpectins and cross-linked with hydroxyproline-rich glycoproteins (20, 101).When the first conceptual models were proposed about twenty years ago,the differences in wall compositions between monocots and dicots were justbeginning to be catalogued (33). Perhaps because of the socioeconomic im-portance of the cereals, the vast majority of the monocots studied weregrasses. Whistler (164) described grasses as rich sources of xylan, and Aspi-nall (1), in a review of plant cross-linking glycans, noted the enrichment ofxylans and mixed-linked glucans in grasses. Wilkie (165) offered the firstcomprehensive survey of the cross-linking glycans of grasses. More recent446 CARPITAAnnu. Rev. Plant. Physiol. Plant. Mol. Biol. 1996.47:445-476. Downloaded from arjournals.annualreviews.orgby University of Georgia on 04/26/06. For personal use only.studies of the carbohydrate and aromatic components of cell walls from abroad spectrum of monocots have revealed that the Poales (family Poaceae,formerly the order Graminales, family Gramineae), their