The investigation of secondary cell wall deposition in differentiating Zinnia cell suspension cultures

The study of plant cell walls has been of great interest for many years because of the importance of the cell wall in plant development and in materials of economic utility such as fiber and wood A plant cell wall is defined as the "layer of structural material found external to the protoplast" (Fry, 1988 p 2) in plant cells. The protective and strengthening characteristics of cell walls influence or possibly regulate the cell's shape, which in the end determines the form and adaptability of a plant (Roberts, 1989). Understanding cell walls and their components can lead to better utilization of plants and provide a possible basis for developing modified plants with increased commercial utility (Shedletzky et al., 1990).

The plant cell wall is now realized to have many critical functions in plant development and survival. These include: (a) regulating plant morphogenesis through controlled orientation of cellulose microfibrils; (b) mediating plant responses to pathogenic and environmental stress; (c) housing a diversity of complex polysaccharides, fragments of which can act as developmental signals; (d) providing an environment for the function of numerous enzymes; and (e) interacting with cytoplasmic components through linker proteins in the plasma membrane to regulate development (Roberts, 1989, 1990). Despite this increase in ascribed importance, our true understanding of wall composition and deposition is in its infancy, particularly for secondary cell walls.