Influence of Gibberellin on Activities of Starch Degradative Enzymes and Phosphatase in Verbascum thapsus

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Abstract
Gibberellic acid was applied near the shoot apical region of rosettes of Verbascum thapsus, a biennial weed, over a 6‐week period. Starch content and the activities of α‐amylase, β‐amylase, glucan phosphorylase and acid and alkaline phosphatase were determined for roots of the rosettes for 5 of the 6 weeks of gibberellin treatment. Starch content decreased during the first week of treatment, and it continued to drop until the third week, at which time virtually no starch remained. There was a concomitant increase in activities of the starch degradative enzymes, all of which reached their respective peaks of activities by the end of the second week of hormonal treatment. The peaks of these enzymatic activities occurred approximately 1 week before appearance of the first morphological signs of bolting. Alkaline phosphatase showed an early response to applied gibberellin, and its peak of activity coincided with early signs of bolting.