The cell walls of green plants and the CGA

      The extracellular matrix or ECM of eukaryotes functions in many diverse ways including providing a buffer/barrier against chemical and physical stressors, serving as a conduit for perception of external stimuli, initiating complex signal transduction cascades and providing a matrix for cell-cell adhesion/recognition and a harbor for key enzymes. In green plants, the cell wall (CW) represents the dominant component of the ECM.  It typically consists of a load-bearing network of cross-linked fibrils, i.e., cellulose microfibrils tethered by hemicellulose, which are embedded in a matrix of pectins and various proteins (e.g. extensins, arabinogalactan proteins or AGPs) (Carpita and McCann 2000, O’Neill and York, 2003).  The CW is of paramount importance to the survival of the plant including defense, regulation of cell expansion, adsorption of key ions and the establishment of communication conduits for both symbionts and pathogens. The plant dedicates a significant amount of its photosynthate to the biogenesis of these CW components. The synthesis of CW polymers is believed to entail the expression of over 1,000 genes. The cell wall is also a highly dynamic structure that modulates in accordance with both genetic and environmental cues and undergoes complex biochemical and structural changes during development (Cosgrove 2005). CWs also profoundly impact human society as they provide food, fibers, building materials (Pauly and Keegstra 2008).
   
CGA cell walls and cell coverings- The extracellular matrix of the CGA may be categorized into three general structural types:

1. SCALES: In the motile phase of such organisms as Mesostigma viride or Chlorokybus atmophyticus (i.e., zoospores) or Chara (i.e., sperm cells), scales coat the plasma membrane and/or flagellar membrane surfaces. To learn more about scales, please click on the image to the right.

2. EPS: Many CGA produce large amounts of an extracellular polymeric substance or EPS. The EPS typically appears as a gel or “mucilage” and
is found  outside the cell wall. To learn more about EPS, please click on the image to the right.

3. CELL WALLS: CGA possess cell walls (CWs) that have significant biochemical and structural similarities to those found in land plants (Domozych et al. 2007a, b, Eder and Lutz-Meindl 2008, Eder et al. 2008, Baylson et al. 2001, Popper and Fry 2003). To learn more about the CGA cell walls, please click on
the image to the right.