Pectin polymers

A FIGURE 6-33 Schematic representation of the cell wall of an onion. Cellulose and hemicellulose are arranged into at least three layers in a matrix of pectin polymers. The size of the polymers and their separations are drawn to scale. To simplify the diagram, most of the hemicellulose cross-links and other matrix constituents (e.g., extensin, lignin) are not shown. [Adapted from M. McCann and K. R. Roberts, 1991, in C. Lloyd, ed.. The Cytoskeletal Basis of Plant Growth and Form, Academic Press,... 

Pectin is a mixture of complex polymers (1-3). These are formed during primary wall formation while the cell wall is expanding in surface area. At these early stages of growth the pectin polymers contribute in a major way to the texture of the wall especially to its ability to expand and stretch. The wall is much more a fluid structure at this time and water is an extremely important constituent. The primary wall when the matrix is non-lignified can be considered as a fluid plastic structure so that any load applied to the wall is transmitted to the microfibrils by the viscous drag of the plastic deformation of the matrix. This can alter very much with the composition and physical state of the matrix materials, especially with that of the pectin complex ( 3). 

The pectin polymers are constituents of the cell plate during cell division and they are the first set of polysaccharides to be... 

The composition of the pectin polymers can be altered by the application of plant growth factors ( ). The texture of fruit and the ripening process depends upon the alteration of the pectin components of the cell walls of fruit tissue. It is apparent that the pectin polymers are a variable and important feature of the young, growing wall. 

The formation of pectin and its assembly for final export across the plasmamembrane will be considered here as a production line to indicate the various limiting steps which are controlled to monitor its production. The various channels for the movement and synthesis will be described separately so that the control points can be assessed. The channels which operate for production and movement of the polymers within the cytoplasm and endomembrane system of the cells are - Channel 1. Production and movement of nucleotide sugar donors. Channel 2. Synthesis and compartmentalization of the pectin polymers within the endomembrane system. Channel 3. Movement of vesicles and fusion with the plasmamembrane for assembly and deposition within the wall. 

Channel 2. Synthesis and Compartmentalization of the Pectin Polymers within the Endomembrane System... 

---