COMPARATIVE ASPECTS OF PLANT MORPHOGENESIS - A CELLULAR, MOLECULAR, AND EVOLUTIONARY APPROACH

Recent research on development and evolution has focused attention upon arabinogalactan proteins, dominated by hydroxyprolines covalently bonded to oligosaccharides. Glycoproteins, ubiquitous in land plants, form distinctive patterns of distribution during development. Applied to cultures of hepatics, inhibitors of proline hydroxylation produce phenotypes mimicking more primitive species. Since glycoproteins are associated chiefly with wall and membrane metabolism, genes controlling glycoproteins may promote adaptive diversity via mutations. Evidence favoring this hypothesis was found by comparisons between major groups of land plants. In angiosperms, specialized cell walls are the rule, but phylogenetic trends involving them are not found. More important are trends in the reproductive structures, well known to taxonomists. With respect to these traits, genotype-phenotype interactions are indirect, involving different gene systems. Recently proposed theories that rely upon undefined morphogens are rejected. Development is epigenetic, based upon successive interactions between regulators produced at various developmental stages, each stage being integrated with those that precede and that follow. To produce an adaptive phenotype, each successive stage is controlled in such a way as to interact favorably with the internal environment present when it appears.