Organogenesis in plants

We all know how life starts, it from a single cell or a very small group of cells called an embryo, that gradually grows and divides into n number of cells to form a whole organism. Have you not ever wondered how a single cell or tissue of uniform cells divides and multiplies into an enormous number of cells that specialise in various functions. This process of transforming unstructured cells into structured and completely organised organs in and developing the embryo of a plant or an animal is called organogenesis.

Organogenesis is a beautiful mystery or rather we should say a beautiful wonder of mother nature. Only a certain number of cells can multiply and divide to transform and form a completely new organ and today, we will talk about how organogenesis occurs in plants.

Organogenesis in plants

The process of development of plant organs such as shoot, flower, and root system from either an ex-plant or from the callus of culture is known as organogenesis in plants.

A completely developed plant consists of organs specialised in a particular function such as roots are responsible for absorbing nutrients and water from the soil, leaves are necessary for photosynthesis, and flowers for reproduction. Tissues such as meristem, cortex, phloem, and epidermis are organised together to form these organs. Developing and initiating these organs is called organogenesis.

 Meristematic cells are responsible for the development of plant organs like the root system, flowers, and shoot system. Shoot apical meristem or shortly known as SAM is responsible for generating or developing organs above the root, later organ. Shoot apical meristem ( SAM ) regenerated organs such as leaves, stems, buds, flowers, etc. hold organogenesis capability on their edges. When these cells are induced in-vitro a whole new plant grows from it. This whole process is called organogenesis.

Dedifferentiation and redifferentiation are the two steps that are involved in organogenesis.

Dedifferentiation is a process that helps in the formation of callus from the tissues of explant with acceleration in cell division. Cells multiply and divide very quickly to grow their number to form undifferentiated cells, i.e. callus, this process of dedifferentiation.

Redifferentiation is the process of developing a permanent organ by converting the cells that were formed during dedifferentiation. Cells lose their capability to multiply and divide in this process so that they can be converted into permanent tissue.

The process of organogenesis can take place in three ways:

· From an explant

· From the callus culture

· From the axillary buds

Types of Organogenesis in plants

There are two types of organogenesis in plants that are:

· Direct organogenesis

· Indirect organogenesis

Direct organogenesis in plants tissue culture

When buds and shoots are directly developed from tissue and there is no need for the callus stage then this process is known as direct organogenesis in plant tissue culture.

Direct organogenesis results in the development of planting material with no genetic variation therefore cloning. Uniformity in the planting material is ensured. This process is also useful in propagating plants with a better multiplication rate (the number of plants per explant is higher).

Direct organogenesis is more of an industrial process as it provides plants with better multiplication rates and cloning propagation where the genetic variation is zero.

Indirect organogenesis in plant tissue culture

In this process of indirect organogenesis, a plant’s organ is developed from the callus of an explant (tissue that developed at the site of a cut or wound). The process of indirect organogenesis is more useful in the development of a transgenic plant. There are two ways that can be used to develop a transgenic plant in the indirect organogenesis method:

·  Transformed callus is used to regenerate a new plant that is transgenic

·  A modified explant is used to develop callus in the shoot, transform explant is initially used.

Factors that affect organogenesis:

We can divide the factors into two major groups that is:

· External factors

· Internal factors

External factors that affect organogenesis are

·  The medium

 The medium has a great impact on organogenesis

·  The chemicals and medicines

Curtain chemicals such as auxin and cytokinin show a great impact on the growth of plant organs such as roots and shoots. Experiments and studies have shown that auxin simulates information of the root system and stops the formation of the shoot. Whereas, cytokinin promotes the development of shoot.

· The environmental conditions

The environment and surroundings play a key role in organogenesis. A good and rich nutrient environment promotes organogenesis whereas a harsh and tough environment does the vice versa.

Internal factors that effects organogenesis are

· Gibberellin

Gibberellins is a hormone that restricts the formation of shoot and root both. Not only this but also gibberellins lower the content of starch and prohibit bud formation.

· Carbohydrates

Carbohydrates work as osmotic agents and as a respiratory energy source. Callus development and growth are affected by osmotic stress. Sucrose which is a form of carbohydrates is essential for this process.

· Ethylene

Ethylene is a hormone that enhances the development process during the primordial process but the process of organogenesis is blocked by ethylene hormones.

Conclusion

The process of development of plant organs such as shoot, flower, and root system from either an ex-plant or from the callus of culture is known as organogenesis in plants. Organogenesis is a process that is basically essential for life. There are two types of organogenesis: direct organogenesis and indirect organogenesis. There are certain internal and external factors that play a key role in the process of organogenesis.