Overall explanation of auxin mechanisms that control vascular differentiation in leaves and organ development in flowers.

Main conclusion: This review on auxin control mechanisms explains the general concept of apical dominance in leaves, flowers and roots, where specific cells or organs that produce high-auxin concentrations inhibit other adjacent tissues or organs, resulting in organized developmental patterns, e.g., the downward (basipetal) development of leaves, organized vein patterns in leaves, synchronized flower development, and optimized root architecture. The various control mechanisms and roles of auxin during leaf and flower development were investigated in the pioneering work of Aloni et al. (Planta 216:841-853, 2003; Planta 223:315-328, 2006a), which explained why and how leaves, flowers and their vascular tissues are regulated in organized patterns. The first paper (Aloni et al. 216:841-853, 2003) tested the leaf venation hypothesis (Aloni, J Plant Growth Regul 20:22-34, 2001) and the second paper (Aloni et al. Planta 223:315-328, 2006a) uncovered the unsolved mystery of floral organ developmental pattern. In this review, the precedence and unique contribution of these studies in explaining the general auxin mechanisms controlling vascular differentiation in leaves and organ development in flowers are presented in conjunction with later work that detailed specific aspects of these mechanisms.