Phase Change in Hedera helix: Induction of the Mature to Juvenile Phase Change by Gibberellin A3

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Abstract
A sensitive and reproducible method to obtain GA3 induced morphological reversion of mature Hedera helix to the juvenile form has been developed. Dose response experiments indicate that GA3 stimulates reversion over a 50–100 fold range with a half maximal response at approximately 0.5 μg GA3 per plant. The individual characteristics involved in phase change revert to the juvenile form in a sequential manner as GA3 dose is increased. Variations in light intensity from 1.2–3.6 × 104 lux and temperature from 15 to 26°C do not affect this hormonal response. Other growth regulators including indoleacetic acid, kinetin, abscisic acid and (2‐chloroethyl)phosphonic acid (Ethephon) are inactive but other gibberellins (GA1 and a mixture of A4–A7) are active in stimulating reversion. Therefore, the response is specific for gibberellins as a class of hormones but non‐specific for a particular form of gibberellin. The significance of this response in relation to juvenility in woody plants is discussed.