Mastering the Art of Bonsai Growth: How to Control Shape and Size with Auxin, Cytokinin and Gibberellin - Bonsai-En

Mastering the Art of Bonsai Growth: How to Control Shape and Size with Auxin, Cytokinin and Gibberellin

What Are Plant Hormones?

 
Hormones in plants, also known as plant growth regulators, are chemical compounds that regulate various physiological processes in plants such as growth, development, and response to environmental conditions. These compounds are produced in small quantities and act in very low concentrations. They are produced in specific parts of the plant, such as the roots, shoots, and leaves, and then transported throughout the plant to where they are needed.
There are several types of hormones in plants, each with a specific role. Some of the main types of hormones in plants include auxin, cytokinin, gibberellin, abscisic acid, and ethylene. These hormones act together in a coordinated manner to regulate various plant processes, including growth, development, and response to the environment. Hormones also play a vital role in the plant's response to stress and injury, and are essential for the survival and reproduction of the plant.
The study of hormones in plants is known as phytohormoneology, and it continues to be an active field of research as scientists work to better understand the complex interactions between hormones and their role in plant growth and development. Understanding how hormones work in plants can also have practical applications in agriculture and horticulture, such as in the development of more efficient and productive crop varieties.
 
 
In this article we will be Discussing the 3 main hormones you will hear about in Bonsai which are Auxin, Cytokinin and Gibberellin and how you can use them to control the growth of a Bonsai Tree.
What's Covered In This Article
  1. Description Of Auxin, Cytokinin & Gibberellin
  2. The Interaction Between Hormones
  3. Polar Cross Talk
  4. How These Hormones Are Used To Control Bonsai
 

Description Of Each Hormone

 

Auxin

 
Auxin is a type of plant hormone that plays a vital role in the growth and development of plants. It is responsible for many processes, including cell elongation, apical dominance, and the regulation of cell differentiation.
Auxin is produced in the apical meristems, or growing tips, of a plant and is transported towards the lower parts of the plant. When auxin reaches the lower parts of the plant, it stimulates cell elongation and expansion, which leads to the formation of new tissue. This process is known as cell elongation.
Auxin also plays a role in apical dominance, which is the phenomenon where the growing tip of a plant, known as the apical bud, suppresses the growth of lateral buds. This allows the plant to direct its energy towards the main stem and promotes upward growth.
 
Auxin also regulates cell differentiation, the process where undifferentiated cells become specialized cells with specific functions. Through this process, auxin controls the formation of roots, leaves, and flowers.
In addition to these functions, auxin also plays a role in the plant's response to gravity, light, and touch. It helps the plant to grow towards light and to respond to touch by bending in the direction of the touch.
Overall, auxin plays a vital role in the growth and development of plants by regulating cell elongation, apical dominance, cell differentiation and also in the plant's response to the environment.
 

Auxin plays a key role in many aspects of plant growth and development. Some of its main functions include:

  1. Cell elongation: Auxin stimulates cell elongation in the stem, leading to the formation of new tissue and the overall growth of the plant.
  2. Apical dominance: Auxin promotes the growth of the apical bud, or the growing tip of a plant, and suppresses the growth of lateral buds. This allows the plant to direct its energy towards the main stem and promotes upward growth.
  3. Root formation: Auxin promotes the development of roots, particularly in the embryonic stage of the plant. It also helps to establish the root-shoot axis, which is the direction of growth of the plant.
  4. Leaf and flower formation: Auxin regulates the formation of leaves and flowers, as well as the differentiation of cells into specialized cells.
  5. Phototropism: Auxin plays a role in the plant's response to light, allowing it to grow towards light.
  6. Gravitropism: Auxin helps the plant to sense gravity and grow in the correct direction.
  7. Stress response: Auxin also plays a role in the plant's response to environmental stress such as drought, high salinity, and cold temperatures.
Overall, auxin is a critical hormone that regulates many aspects of plant growth and development, from cell elongation and apical dominance to root formation and stress response. It helps the plants to adapt to the environment and to grow in the correct direction. Understanding the role of auxin in plant growth and development can help in developing more efficient and productive crop varieties.
 
 

Cytokinin

 
Cytokinin is a type of plant hormone that plays a role in cell division and differentiation, as well as in the growth and development of plants. It is responsible for many processes, including cell division, cell differentiation, and the regulation of shoot growth.
 
Cytokinin is produced in the roots, shoots, and developing seeds of a plant. It is transported to the upper parts of the plant, where it promotes cell division and differentiation. This process leads to the formation of new tissue and the overall growth of the plant.
 
Cytokinin also promotes shoot growth by stimulating cell division in the shoot apical meristem, which is the growing tip of the plant. This leads to the formation of new leaves and branches, which in turn increases the overall size of the plant.
 
In addition to these functions, cytokinin also plays a role in the plant's response to environmental stress, such as drought and high salinity. It helps the plant to adapt to these stressors by promoting the growth of roots and by regulating the expression of stress-responsive genes.
 
Cytokinin also plays a role in regulating the balance between cell division and differentiation, and between root and shoot growth. This balance, known as the shoot-root balance, is important for the overall growth and development of the plant.
 
Overall, cytokinin plays a vital role in the growth and development of plants by promoting cell division and differentiation, shoot growth, and the plant's response to environmental stress. Understanding the role of cytokinin in plant growth and development can help in developing more efficient and productive crop varieties.
 

Gibberellins

 
Gibberellin is a type of plant hormone that plays a key role in plant growth and development. It is named after the fungus Gibberella fujikuroi, from which it was first isolated.
Gibberellins are a group of over 130 different compounds that are involved in many aspects of plant growth and development, including cell elongation, stem growth, seed germination, and the development of flowers and fruits.
Gibberellins promote cell elongation by stimulating the cells to grow in length, which leads to the formation of new tissue and the overall growth of the plant. They also promote stem growth by stimulating the activity of the apical meristem, which is the growing tip of the plant, leading to the formation of new leaves and branches.
 
Gibberellins also play a key role in seed germination by breaking seed dormancy and promoting the growth of the embryonic stem and leaves. They also promote the development of flowers and fruits by stimulating the growth of the reproductive organs.
 
Gibberellins also play a role in the regulation of photoperiodism and the plant's response to environmental stress, such as drought and high salinity.
Overall, gibberellins are an important group of plant hormones that play a key role in many aspects of plant growth and development, including cell elongation, stem growth, seed germination, and the development of flowers and fruits. Understanding the role of gibberellins in these processes can help in developing more efficient and productive crop varieties.
 
Gibberellins play a crucial role in plant growth and development, particularly in stem elongation. They promote cell elongation by stimulating the cells to grow in length, which leads to the formation of new tissue and the overall growth of the plant.
 
Gibberellins promote stem growth by stimulating the activity of the apical meristem, which is the growing tip of the plant. This leads to the formation of new leaves and branches and the elongation of the stem. They do this by stimulating the cells in the meristem to divide, which leads to the formation of new cells that will eventually differentiate into different plant tissues.
Gibberellins also play a role in the regulation of photoperiodism, which is the plant's response to the length of daylight. They promote stem elongation in long-day plants by stimulating the activity of the apical meristem, leading to the formation of new leaves and branches and the elongation of the stem. In short-day plants, they inhibit stem elongation, which promotes the formation of flowers.
 
Gibberellins also help plants to cope with environmental stress, such as drought and high salinity, by promoting stem elongation. This allows the plant to reach for water and light more efficiently, which helps to improve its survival rate.
In horticulture, gibberellins are used to increase the height of plants and improve their overall growth and development. For example, they are used to promote stem elongation in fruit trees, which increases the yield of the crop. They are also used to promote stem elongation in ornamental plants, which improves their appearance and marketability.
Overall, gibberellins play a critical role in the growth and development of plants, particularly in stem elongation. They promote cell elongation by stimulating the cells to grow in length, which leads to the formation of new tissue and the overall growth of the plant. They also play a role in the regulation of photoperiodism and the plant's response to environmental stress, which helps to improve the survival rate of the plant.
 

Interaction between hormones

 
these hormones in the plant affect the growth and development. When cytokinin to auxin ratio is high, the cell division is stimulated, when auxin to cytokinin ratio is high, the cell elongation is stimulated. Similarly, when the ratio of gibberellin to cytokinin is high, the cell elongation is stimulated and when the ratio of cytokinin to gibberellin is high, the cell division is stimulated.
 
Maintaining the correct balance of hormones in plants is crucial for their overall health and growth. When the balance is disrupted, it can lead to a variety of problems, including stunted growth, abnormal development, and even plant death.
 
Auxin, cytokinin, and gibberellin work together to regulate various aspects of plant growth and development. For example, auxin promotes cell elongation and stem growth, while cytokinin promotes cell division and growth. Gibberellin promotes stem growth and seed germination. In a healthy plant, the balance of these hormones is carefully regulated, with the right amount of each hormone present at the right time and in the right place.
However, when the balance of hormones is disrupted, it can lead to a variety of problems. For example, if there is an excess of auxin, it can inhibit the growth of lateral branches and cause the plant to become elongated and spindly. This can also cause the plant to become more susceptible to disease and pest infestation. Similarly, an excess of cytokinin can cause the plant to become stunted and thickened.
 
On the other hand, a deficiency of auxin can cause the plant to become stunted and bushy, with small leaves and reduced growth. Similarly, a deficiency of cytokinin can cause the plant to become elongated and spindly, with a reduced number of branches and leaves. A deficiency of gibberellin can also cause the plant to become stunted, with smaller leaves and reduced growth.
To maintain the health of plants, it is important to ensure that the balance of hormones is maintained. This can be done by providing the right conditions for growth, such as adequate light, water, and nutrients, and by controlling factors that can disrupt the balance of hormones, such as pests and diseases. Additionally, in horticulture and agriculture, hormone manipulation can be done through the use of synthetic hormones and growth regulators to help promote healthy plant growth and development.
 
While the health of the plant is paramount while in the maintenance stage of a bonsai journey you can see how we can use these hormones to our advantage. Take Auxin for example, if we leave the auxin in the growing tip we get long spindly branches, but if we remove the Auxin we active the auxiliary buds and get ramification. The same can be said if we cut the roots, now we have more auxin present then Cytokinin which results in the excess Auxin working to get that balance back in the Root to Shoot ratio I.E repairing the root system after root work has been done.
 
For a better description see the next section of Polar Cross Talk.
 

Polar Cross Talk

 
Polar cross talk refers to the communication between cells on opposite sides of a plant's stem or root, which allows for the coordination of growth and development. This communication occurs through the movement of hormones, such as auxin, cytokinin, and gibberellin, through the plant's vascular system.
Auxin, for example, is transported from the shoot to the root and can signal to the root to grow. Cytokinin, on the other hand, is transported from the root to the shoot and can signal to the shoot to grow.
 
Polar cross talk plays a crucial role in the overall growth and development of a plant. For example, it allows for the proper coordination of root and shoot growth, which is necessary for the plant to be able to efficiently absorb water and nutrients from the soil, while also being able to photosynthesize and produce food.
 
It also allow for the proper coordination of apical dominance and lateral branching. Apical dominance is the tendency of the terminal bud of a stem to inhibit the growth of axillary buds. The auxin transported from the shoot to the root signals to the root to inhibit lateral branching which helps the plant to be taller and straighter which allows for better light absorption.
Polar cross talk is also important for the proper differentiation of cells, which is necessary for the proper formation of roots, stems, leaves, and other plant organs.
 
In summary, polar cross talk is the communication between cells on opposite sides of a plant's stem or root, which allows for the coordination of growth and development. This communication occurs through the movement of hormones such as auxin, cytokinin, and gibberellin. It plays a crucial role in the overall growth and development of a plant, allowing for the proper coordination of root and shoot growth, apical dominance and lateral branching, and the proper differentiation of cells.
 

How These Hormones Are Used To Control Bonsai

 
Auxin, which promotes stem elongation and root growth, is often used to control the shape of the bonsai tree. By allowing auxin to reside in the the top of the tree, the growth of the upper branches is promoted, while the growth of lower branches is suppressed. This helps to create the desired shape of the bonsai tree by allowing branches with auxin to grow to either get length or thickness. Similarly, by applying auxin to the roots by reducing the cytokinin which is done when trimming roots, the growth of the root system can be promoted, which is important for maintaining the health of the bonsai tree especially after repotting or potting into refinement for the first time.
 
Cytokinin, which promotes cell division and growth, is often used to promote the development of new buds and branches on a bonsai tree. By allowing cytokinin to move to specific areas of the tree by removing the auxin from that area ( cutting the growing tip ), the growth of new branches can be promoted, which helps to create a fuller, more intricate bonsai tree ( ramification ).
Gibberellin, which promotes stem elongation and seed germination, is often used to control the overall size and shape of the bonsai tree. By allowing gibberellin to reside in the tree, the stem elongation can be promoted, which helps to create a taller tree with elongated growth which can speed up the thickening process in the development of young stock.
 
It's important to note that controlling the growth of bonsai trees is a delicate process, and requires a balance of these hormones. An excess of one hormone can lead to undesirable growth patterns and even harm the tree. Therefore, it's important to work with a bonsai expert to find the right balance and dosage of hormones to use.
bonsai artist with bonsai tree

Author : Joshua Hooson

Joshua Hooson is an author and enthusiast of the art of bonsai. He has built his knowledge and understanding of bonsai through a combination of self-experience, lessons learned through hands-on practice, and extensive research. His articles reflect his passion for the subject and offer insights gained through his own personal journey in the world of bonsai. All the information provided in his works is a result of his own experiences and the knowledge he has gained through his studies. He is dedicated to sharing his love of bonsai and helping others grow in their understanding and appreciation of this ancient and beautiful art form.

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