Regulation of Cell Wall Synthesis in Avena Stem Segments by Gibberellic Acid

Gibberellic acid induces (a) increased elongation of Avena sativa stem segments, (b) increased formation of cell wall material, measured on the basis of dry weight, and (c) increased incorporation of (14)C-glucose into all fractions of the cell wall material. This increased incorporation of radioactivity correlates well with increased formation of cell wall material and shows a time-course pattern similar to the time course of the elongation response. Approximately one hour after the application of gibberellic acid, the rates both of growth and of incorporation of radioactivity accelerate to about 2-fold over the control rate. Gibberellic acid does not stimulate the incorporation of labeled glucose into the cell wall material simply by increasing the rate of uptake of glucose by internodal cells. The stimulation of the incorporation of (14)C-glucose into cell wall material, which reflects the stimulation of cell wall synthesis, seems to be an important and relatively early effect of gibberellic acid in this system and probably contributes significantly to the elongation response elicited by the hormone.