Phase Change in Hedera helix: Stabilization of the Mature Form with Abscisic Acid and Growth Retardants

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Abstract
Applications of ABA to the mature form of Hedera helix stabilize its morphological characteristics and prevent GA3 induced reversion to the juvenile form. Plants treated with GA3 reverted to the juvenile form whereas those supplied with ABA in conjunction with GA3 remained mature. When mature plants were treated with 5 nanomoles of GA3 and 5 micromoles of ABA, reversion did not occur, but when the GA3 dose was raised to 25 nanomoles with the same level of ABA, reversion did occur. This implies that the relative amounts of GA3 and ABA applied are important in controlling growth form and not the absolute levels of these hormones. Applications of growth retardants (Chlormequat, Ancymidol, and SADH) stabilize the mature form by preventing spontaneous reversions induced under low light intensity. These two lines of evidence support the hypothesis that the mature morphological form can be stabilized by regulating the effective level of gibberellins in the plant and this can be accomplished by inhibition of gibberellin action or gibberellin biosynthesis.