Gibberellins and the changes in Ivy

In this post I'd like to talk about a compound that has certain characteristics that control the way plants grow. The plant I've chosen to demonstrate some of these changes is Hedera helix, otherwise known as Ivy, in which the gibberellin controls maturity, root promotion and the leaf shape.

History
Gibberellin is a plant growth regulator and is used for various applications commercially. It was originally discovered in Japan in the early 20th century by scientists researching fungus in rice plants, whereby when the rice plants were affected by a certain disease (bakanae) the plants became very long and when it was windy, the wind blew the rice plants over and the rice was lost. Further work was done in the 1950s the result of which was that a range of chemicals were extracted that made cells elongate, the first gibberellin was called Gibberellic Acid. There are now known to be over 100 types of gibberellin and they are known to be widespread in flowering and non-flowering plants, being present in roots, young shoots and seeds.

Characteristic of Gibberellin
1) Cell elongation (This charateristic is used commercially on grapes to make the cells elongate so that the grape is bigger due to holding extra water. As gibberellins are natural there is no issue with genetic modification, but it's worth noting that this technique doesn't increase nutrition. This can be seen with large oval grapes when compared to the normal quite small and round grapes).
2) Stimulate flowering.
3) Stimulate increase in size of tissues (Flowers treated commercially to increase flower size include Camellias).
4) Control plant maturity. The gibberellins favour the juvenile conditions.
5) Assists seeds to come out of dormancy (used commercially by the brewing industry by making the germination to start thereby making the endosperm change starch to sugar(malt)).

Gibberellins in Ivy

The forth characteristic is the one that I'd like to talk about in this post as it is involved in the changes that occur during the life cycle of ivy (Hedera helix). The life cycle of the ivy has two stages of growth; the first is the juvenile stage and this is eventually followed by the adult stage.

Juvenile Stage

The photo to the left shows the juvenile stage of the ivy. The well known Ivy leave shape with lobed leaves. During this state the ivy gets around, growing extensively and is able to lay down may sets of roots through leaf nodes along its stem as it does so. During this stage the ivy cannot flower. The ivy elongate will try to grow upwards and after a length of time will enter its adult phase.

Adult Stage

When the ivy enters the adult stage, the plant stem can no longer create roots. The plant will become erect and bush out and the leaf shape will change, becoming smoother around the edges. The plant will then flower during autumn and will then make berries that are often eaten by birds during the following Spring.







The photo below shows both juvenile and adult stages of ivy. With the juvenile stage at the bottom of the photo directly above the woody stem and the adult stage from around half way up to the top of the photo. It is known that if gibberellin is applied to the adult stage of ivy that the adult form will refert to the juvenile form. There are other plants that show similar traits of root promotion and leaf change, including eucalyptus.