Gibberellins primarily develop in the plant’s shoots, buds and seeds. They are involved in breaking the cycle of dormancy in the seeds and in the process of seed growth signals. They promote extra length and fast growth of cells between the plant’s nodes and in the leaves. It is these hormones that are responsible for driving the plant rapidly upwards, making it long and spindly, in low light conditions.
The shorter the distance between the nodes of a plant, (the point from which each leaf shoots) the more efficient the plant will be in relation to its root size. This is because the taller it is the more energy it will need to use for growing the thicker, longer stems needed to hold the extra weight. Also it will use more energy to transport its plant sugars over the greater distances.
Another reason, in indoor plants, is that the taller the plant is the steeper the angle of shade becomes making a greater space necessary for its neighbouring plants.
Artificial light halves in intensity for each foot from the source, meaning the leaves at the bottom of the plant are getting weaker light than those at the top. The taller the plant grows the further away the lamp must be placed and so the weaker still the light intensity impinging on the bottom layers.
A final drawback with tall plants is that the CO2 needed by the plant will tend to collect at the lower levels because it is heavier than air. This will make getting it to the upper levels more difficult and of course, ultimately, more costly.
It is obviously better to limit the height growth and increase the potential yield gained by this action. The Gibberellins within the plant will slow the growth of the stem cells under good light levels. Increase the light intensity and the growth will be transferred from height to root ball and plant density. Remember, the more root and leaves, the more flowers, fruit and seeds.
The complicated interaction of Auxins and Gibberellins is responsible for the way in which the plant reacts to the available light. The Auxins make it turn towards the brighter light while the Gibberellins slow its growth when the optimum light intensity is reached. Outside, in the sunshine, this is a very delicate and complex interaction as the light varies from day to day and month to month.
There are in excess of 70 different types of Gibberellins that assist in the germination of seeds, the elongation of stems and leaves and also affect the development of fruit.
Auxin-Gibberellin sprays are used by commercial growers to promote the growth of some fruits such as apples, currants and eggplants without fertilization. An example of one interesting use for Gibberellins is in the production of the Thompson variety of seedless grapes.
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