Hormone transport and action in the green shoot: long-term studies of a clonal stock of Coleus blumei (Labiatae)

A decades-long study of hormone production, transport, developmental actions, and hormonal interactions in the green shoots of mature plants has exploited a clone of Coleus blumei. To obtain data both quantitative and reproducible, we greatly increased sample size over the classical anatomical models, initiated round-the-clock collections, and countered that increased workload by clearing and staining organs rather than by embedding and serially sectioning them. Major developmental events occurred at night. The control of the normal differentiation and regeneration of tracheary cells and sieve-tube members by indole-3-acetic acid (IAA) and cytokinins and of fibers by IAA and gibberellic acid have been major findings from this approach. IAA from the leaf blade controls the timing of leaf abscission. As the leaf ages, the ability of the petiole to transport IAA from the blade to the abscission zone declines, with abscisic acid (ABA) decreasing IAA transport down the petiole and concomitantly increasing the conjugation of IAA with aspartic acid. Evidence for transport barriers was found at nodes and abscission zones