In-vivo binding of radioactive gibberellins in dwarf pea shoots.

When shoots of 6-day-old, dark-grown peas were excised 30 mm below the apex and floated on a solution of radioactive gibberellin A 1 ((3)H-GA1) or radioactive gibberellin A5 ((3)H-GA5), more radioactivity accumulated in the apical part of the stem which responds to GA than in the basal, unresponsive region. The accumulation of (3)H-GA1 was, however, less pronounced than the accumulation of (3)H-GA5. GA derivatives of very low biological activity were not taken up preferentially by the apical region of the stem. Light, which lowers the responsiveness of dwarf peas to GA1 and particularly to GA5, also reduced the accumulation of these GAs in the apical part of the stem. Sections from the GA-responsive region were able to retain a higher level of GA5 than sections from the non-responsive, basal region. The accumulation and retention of GA in the hormone-responsive tissue may be due to binding of the hormone to specific GA receptors.