The plant cell surface and plant development

In normal development in multicellular plants, the directions of cell division and of cell enlargement play essential roles in the form assumed by a plant and its organs. Tissue development requires that cellular controls such as division and enlargement act locally. Some tissues (such as the vascular tissues of roots and shoots) display radial symmetry, while others (such as the component tissues of angiosperm ovules) are symmetrical only about a longitudinal axis. However, the structural basis of pattern control and of cell determination cannot be explained purely in terms of the direction of division and of the composition of cell walls (affecting enlargement). Patterning requires that certain cells or cell aggregates close to apical meristems become determined to particular developmental fates, and then differentiate accordingly. The position of these cells in the plant body must be controlled carefully, since all of organogenesis depends upon their differentiation. Somehow, cells acquire positional information early on.

Analysis of the control of plant cell fate is an intractible experimental problem. Genes have been identified that are involved with the control of complex developmental processes such as flowering (Coen et al., 1991), but these appear to affect floral organ identity. Other genes encode structural proteins and glycoproteins in plant cell walls that are developmentally regulated and hence candidates for intercellular interactions (Hong et al., 1989; Keller et al., 1989; Ye & Varner, 1991), but these seem to affect the mechanical properties of the cells rather than control their fate.