Gibberellins in Diffusates from Shoots of Apple Trees

Excised shoot apices, leaves and internodes from shoots of apple trees (Malus×domestica) give off gibberellins by diffusion on agar. A methanol extract of the agar was prepared, the extract separated on thin layer plates, and the gibberellin activity estimated by means of Rumex and lettuce hypocotyl bioassays. The largest amounts of gibberellin are found in diffusates from the shoot apex, the two upper leaves and the two upper internodes. Several promotive fractions are found on the chromatograms as well as growth inhibitors. Removal of young leaves retards elongation of the internodes. Probably gibberellins produced in young leaves exercise some control over this process. The growth regulators Alar and CCC also retard internode elongation. Diffusates from shoots treated with these substances were also examined. Preliminary results suggest that the amount of diffusible gibberellins from treated shoots is not reduced.