Plant Tissues
The integration of cells into tissues in plants is fundamentally different from the assembly of animal tissues, primarily because each plant cell is surrounded by a relatively rigid cell wall.
The plant cell wall comprises layers of cellulose microfibrils embedded within a matrix of hemicellulose, pectin, extensin, and other less abundant molecules.
Cellulose, a large, linear glucose polymer, assembles spontaneously into microfibrils stabilized by hydrogen bonding.
The cell wall defines the shapes of plant cells and restricts their elongation. Auxin-
Adjacent plant cells can communicate through plasmodesmata, junctions that allow molecules to pass through complex channels connecting the cytosols of adjacent cells (see Figure 20-42).
Tunneling nanotubes in animal cells are somewhat analogous to plant plasmodesmata in that they are tubelike projections of plasma membranes that form a continuous channel connecting the cytosols of nearby cells (see Figure 20-43).
Plants do not produce homologs of the common adhesion molecules found in animals. Only a few adhesion molecules in plants have been well documented to date.