GENERAL ASPECTS OF PHASE CHANGE, WITH SPECIAL REFERENCE TO HEDERA HELIX L.

One of the most characteristic features of phase change in woody plants is the relatively stable nature of the two phases and the retention of adult characters even after propagation by cuttings or grafting.
Studies on the endogenous hormone levels in English ivy (Hedera helix L.) have shown that the apices of juvenile shoots contain significantly higher gibberellin levels than do adult shoot apices.
The roots also contain high gibberellin levels and there is evidence that the shoots of ivy depend upon the supply of gibberellins from the roots.
It is suggested that prostrate ivy vines growing on the soil surface remain juvenile because of the proximity of nodal adventitious roots to the shoot apices and the maintenance of high gibberellin levels there.
It appears that one of the conditions for transition to the adult state may be the establishment of a certain distance between the roots and shoot apices, with an associated decline in endogenous gibberellin levels in the shoot apices.
However, other factors also appear to be involved.
It is suggested that there are intrinsic differences between the meristematic cells of the apices of juvenile and adult shoots, which are thus ‘determined’ with respect to their developmental potentialities.
The problems associated with the maintenance of the determined state through mitosis are discussed.
The properties of transitional forms of ivy, intermediate between the juvenile and adult phases, are described and their implications discussed.
Analogies are drawn between juvenility phenomena in woody and in herbaceous species.

Symposium on Juvenility in Woody Perennials

P.F. Wareing, V.M. Frydman

https://doi.org/10.17660/ActaHortic.1976.56.4