Plant cell-walls interconnections

The complex nature and interconnectivity of plant cell wall polymers preclude straightforward enzymatic digestion. There are dozens of enzyme families involved in plant cell wall hydrolysis, including cellulases, hemicellu-lases, pectinases, and lignin-modifying enzymes. The Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (IUBMB) has classified cellulases and hemicellulases, like all enzymes, into different classes based on activity. Table 33.2 and Table 33.3, compiled from the IUBMB enzyme nomenclature database (http //www.chem.qmul.ac.uk/iubmb/ enzyme/), list the IUBMB enzyme classifications for cellulases and hemicellulases.153... 

The cell walls are composed of microfibrils interconnected by hemicelluloses. Other polymers such as pectin and lignin fill up the space between cellulosic microfibrils and hemicelluloses. Cells are connected to neighboring cells by middle lamellae, the thin lignin-rich outermost layer of the cell wall (Taherzadeh and Jeihanipour, 2012). The primary cell wall is the outer layer containing cellulose microfibrils arranged in random. The secondary cell wall is differentiated into outer (SI), middle (S2), and inner (S3) layers (Figure 3.1). The thickness of each layer differs, but the S2 layer is the thickest and constitutes the major part of the plant cell wall (Taherzadeh... 

Keegstra K, Thlmadge K W, Bauer W D, Albersheim P 1973 The structure of plant cell walls. III. A model of the walls of suspension-cultured sycamore cells based on the interconnections of the macromolecular components. Plant Physiol 51 188-196... 

Keegstra, K., K. W. Talmadge, W. D. Bauer, and P. Albersheim The Structure of Plant Cell Walls. III. A Model of the Walls of Suspension-cultured Sycamore Cells Based on the Interconnection of the Macromolecular Components. Plant Physiol. 51, 188 (1973). 

In fact, membranes generally serve as the main barrier to water flow into or out of plant cells. The interstices of the cell walls provide a much easier pathway for such flow, and hollow xylem vessels present the least impediment to flow (such as up a stem). Consequently, the xylem provides a plant with tubes, or conduits, that are remarkably well suited for moving water over long distances. The region of a plant made up of cell walls and the hollow xylem vessels is often called the apoplast, as noted above (Chapter 1, Section 1.1D and in Section 9.4A). Water and the solutes that it contains can move fairly readily in the apoplast, but they must cross a membrane to enter the symplast (symplasm), the interconnected cytoplasm of the cells. 

Plant cells can communicate directly through specialized cell-cell junctions called plasmodesmata, which extend through the cell wall. Like gap junctions, plasmodesmata are open channels that connect the cytosol of a cell with that of an adjacent cell. The diameter of the cytosol-filled channel Is about 30-60 nm, and plasmodesmata can traverse cell walls as much as 90 nm thick. The density of plasmodesmata varies depending on the plant and cell type, and even the smallest merlstematic cells have more than 1000 interconnections with their neighbors. 

Most organics can be readily taken up by plant roots and foliage. The chemicals can be transported in living plant tissue (symplast) and nonliving tissue (apoplast). Enzymes in the symplasts may metabolize the chemicals into less toxic compounds. Toxic organics are translocated in cell walls and xylem (apoplast) that form on interconnected continuum within plants. 

In addition to eliminating the porous support tube, the active length of the cells was continually increased to Increase the power output per cell a greater cell power output decreases the number of cells required in a given power size generator and thus improves power plant economics. The active length (the length of the interconnection) was Increased from 30 cm for pre-1986 thick-wall PST cells to 150 cm for today s commercial prototype air electrode-supported cells. Additionally, the diameter of the cells has been... 

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