Some aspects of leaf abscission in Coleus blumei.

The anatomical and histological development of the abscission zone is related to the growth of the leaf blade. It is shown that the initiation of the abscission zone coincides with a profound change in growth type of the leaf blade and a drop in the level of auxin in the leaf blade. Changes in volume and shape of the cells of the abscission zone and adjacent tissue are observed during the development of the leaf and at separation. The response of explants taken from leaves at all stages in development to a wide range of concentrations of IAA is determined. Phases in the abscission process are demonstrated and it is shown that the process is partly reversible, and independent of tissue outside the abscission zone. The fate of IAA applied to explants is investigated by various techniques using radioactive IAA. Microautoradiographs were made of the abscission zone and adjacent tissue. The concentration of IAA in the abscission zone relative to adjacent tissue is determined and turnover of IAA in the abscission zone demonstrated. It is shown that some of the IAA is decomposed in the abscission zone and its methyl group involved in the synthesis of a new molecule.