Fundamental concepts of leaf morphology and morphogenesis: A contribution to the interpretation of molecular genetic mutants

As an older and more established discipline, plant morphology is an important but relatively underutilized resource for the interpretation of mutants. Plant morphology has the potential to provide the context for molecular genetic investigations, especially those concerned with leaf morphogenesis. This article first reviews the basic organization of vascular plants and the relationship of anatomy to morphology in interpreting gene expression. It demonstrates that these two levels of organization are relatively independent of one another and that anatomy cannot be substituted for morphology in analyzing the effects of genes on leaf development. Morphological principles are then applied to two aspects of leaf development, transectional symmetry and leaf dissection. According to this perspective, so-called organs in plants are simply regional expansions that carry specific cell and tissue types in a particular orientation in space. Rather than considering specific genes as determining particular organ types, it is more likely that gene expression itself is dependent on the morphological, developmental context in which the genes are expressed.