The chemical structures of the primary cell walls of the grasses and their progenitors differ from those of all other flowering plant species. They vary in the complex glycans that interlace and cross-link the cellulose microfibrils to form a strong framework, in the nature of the gel matrix surrounding this framework, and in the types of aromatic substances and structural proteins that covalently cross-link the primary and secondary walls and lock cells into shape. This review focuses on the chemistry of the unique polysaccharides, aromatic substances, and proteins of the grasses and how these structural elements are synthesized and assembled into dynamic and functional cell walls. Despite wide differences in wall composition, the developmental physiology of grasses is similar to that of all flowering plants. Grass cells respond similarly to environmental cues and growth regulators, exhibit the same alterations in physical properties of the wall to allow cell growth, and possess similar patterns of wall biogenesis during the development of specific cell and tissue types. Possible unifying mechanisms of growth are suggested to explain how grasses perform the same wall functions as other plants but with different constituents and architecture.

Structure and biogenesis of the cell walls of grasses

In meristematic and differentiating cells, walls have to withstand osmotically generated turgor pressures that may reach values around 3 to 10 bar (0.3-1 MPa) (Carpita and Gibeaut, 1993; Cosgrove, 1993). Walls must be constructed so as not to fail under these conditions. The aggregate strength of noncovalent forces between wall polymers appears to make this possible. There is little evidence that covalent cross-linking between wall polymers is necessary to achieve this stability (see Talbott and Ray, 1992, for a discussion). The results with 2,6-dichlorobenzonitrile-adapted tomato and tobacco cells in suspension culture indicate that although the cellulose-xyloglucan network in these walls is greatly reduced, the cells remain viable under normal osmotic conditions (Shedletzky et al., 1992). In these adapted cells the integrity of the walls appears to be dependent on increased amounts of Ca2\"-bridged pectates. The altered walls have a lower tensile strength, but their porosity is the same as for walls of nonadapted cells. The situation is somewhat different in the case of barley, a graminaceous monocotyledon. Here, the adapted cells have elevated glucuronoarabinoxylan and (1--3,1--4)-f-glucan contents and a lowered cellulose content (Shedletzky et al., 1992). In addition, there is an increase in ester-linked phenolic acids, especially PCA, and an increase in polysaccharides released after esterase treatment. Covalent cross-linking could be involved and extension might involve transesterification. Walls must not only resist turgor pressure, they must also allow wall expansion during cell growth. Cosgrove (1993) has discussed a mechanism by which stress relaxation in

Covalent Cross-Links in the Cell Wall.

A semi-automated in vitro gas production technique for ruminant feedstuff evaluation

Multiphasic analysis of gas production kinetics for in vitro fermentation of ruminant feeds

In vitro gas measuring techniques for assessment of nutritional quality of feeds: a review

https://assets.publishing.service.gov.uk/media/57a08dc3ed915d622c001b6f/R4338b.pdf

Alex B. McAllan

Papers

A simple gas production method using a pressure transducer to determine the fermentation kinetics of ruminant feeds.

Light-induced isomerization and dimerization of cinnamic acid derivatives in cell walls