Growth factors

All sorts of chemicals play a role in plant development 

In plants, like in animals, hormones are chemical messengers that carry information from one part of the organism to another.

Some of the most important hormones in plants are often called growth factors or growth substances, because of the specialised role they play in development. Auxins, which control cell growth, enable a plant on a window ledge to lean towards the sun by causing the cells on the shaded side to elongate, extending the stem on that side. This phenomenon is known as phototropism – movement or growth in response to light. Other tropisms include gravitropism (in response to gravity) and thigmotropism (in response to touch or contact).

There are another four major types of plant growth factors: gibberellins, cytokinins, ethene (or ethylene) and abscisic acid.

Plant growth factor What they are responsible for Where they are found
Auxins  including indole acetic acid (IAA) Cell elongation and expansion; prioritisation of stem tip growth over side shoot growth (apical dominance); responses to light, gravity and water (tropisms); keeping leaves on plants Made in growing points called meristems, but present all over the plant, especially shoots, tips and roots
Gibberellins Stem elongation between leaves; seed germination; fruit growth Mostly in seeds, roots and stems
Cytokinins Cell division; generation of new roots and side shoots (lateral buds) Produced in roots and embryos and travel up via water-transporting xylem, also produced in fruits
Ethene (ethylene) Ripening, rotting and leaves falling; many growth and development processes Produced in almost all parts of the plant but mostly in locations where cell division takes place
Absisic acid Drought signalling, causing stomata to close to save water; seed dormancy (opposing seed germination promoted by gibberellins) Made in parched leaves, roots and developing seeds

Sometimes these chemicals work together, while at other times they may work against, or antagonise, each other. Auxins keep leaves on the plant, while ethene makes them fall off.

These growth factors allow plants to respond to many of the challenges that life throws at them by changing their structure. Many normal plant cells are totipotent, meaning they can give rise to any type of plant cell and even lead to a fully grown plant. With the correct chemicals, tiny samples of plant material – sometimes even single cells – cultured in the lab can grow into entire plants. Very few animal cells have this ability; in humans, only the first 16 cells, starting with the zygote, are totipotent.

Lead image:

Experiment in which beansprouts on the right were treated with gibberellic acid.

Lenore Edman/Flickr


About this resource

This resource was first published in ‘Plants’ in May 2016.

Cell biology, Immunology
Education levels:
16–19, Continuing professional development