Instructive roles for hormones in plant development

Plants, like animals, construct their body following modular sets of instructions that determine cell fate, morphogenesis and patterning, among other building requirements. Hormones regulate plant growth in different ways, and there is increasing evidence for a decisive function of certain hormones in the establishment of developmental programs, equivalent to the role of peptidic molecules and signals of another nature in animal embryo development. Here, we review this role of hormones as instructive agents, and illustrate it with examples such as the generation of morphogenetic gradients by auxin (which determine organ patterning and phyllotaxis), the specification of cell fate at the shoot meristem by gibberellins and cytokinins, the switch between alternative developmental programs (photo- and skotomorphogenesis) by gibberellins and brassinosteroids, and the decision between pistil senescence or fruit growth after anthesis.