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

Abstract

A decades-long study of hormone production, transport, developmentalactions, and hormonal interactions in the green shoots of mature plantshas exploited a clone of Coleus blumei. To obtain data bothquantitative and reproducible, we greatly increased sample size over theclassical anatomical models, initiated round-the-clock collections, andcountered that increased workload by clearing and staining organs ratherthan by embedding and serially sectioning them. Major developmentalevents occurred at night. The control of the normal differentiation andregeneration of tracheary cells and sieve-tube members byindole-3-acetic acid (IAA) and cytokinins and of fibers by IAA andgibberellic acid have been major findings from this approach. IAA fromthe leaf blade controls the timing of leaf abscission. As the leafages, the ability of the petiole to transport IAA from the blade to theabscission zone declines, with abscisic acid (ABA) decreasing IAAtransport down the petiole and concomitantly increasing the conjugationof IAA with aspartic acid. Evidence for transport barriers was found atnodes and abscission zones.