Cytokinins: Definition, Functions, Uses, Structure, Topics

What are cytokinins?

This group of plant hormones induces cell division and differentiation and, consequently, greatly impacts many areas of plant growth and development. Cytokinins were initially identified in the 1950s as a class of molecules that promoted the division of plant cells. The first to be identified was extracted from coconut milk.

They were then chemically synthesised. They are involved in controlling the growth of shoots and roots, senescence of leaves, and mobilizing nutrients to develop seeds or other storage organs and promoting chloroplast formation. For agriculture and horticulture, cytokinins play a vital role in enhancing crop yield, improving the health of plants, and extending the shelf life by delaying leaf senescence and hence facilitating stress tolerance

Chemical Structure and Types of Cytokinins

The structure of cytokinins is described below-

Chemical Structure

Cytokinins share a basic structure of purine and adenine with a bicyclic ring system. The structural variation among the different types of cytokinin is the variation in the side chain attached to the purine ring; they determine the bioactivity of the molecule and its stability.

Types of Cytokinins

• Natural cytokinins

Natural cytokinins include Zeatin, which was isolated from corn kernels, and Kinetin, which was also isolated from herring sperm DNA.

• Synthetic cytokinins (e.g., 6-Benzylaminopurine)

Synthetic cytokinins are those that have been engineered to be more stable and more beneficial concerning their intended use, such as 6-Benzylaminopurine.

Functions of Cytokinins in Plants

The function of cytokinin is described below-

Cell Division and Growth

Cytokinins promote cell division and cell expansion, thus playing a crucial role in shoot and root growth. Through the induction of mitosis, cytokinins allow for an overall increase in plant growth and the growth of new tissues.

Leaf Senescence

These hormones enhance delayed leaf senescence keeping the content of the chlorophyll and also preventing the falling of the leaves at an early stage. This extends the period of leaf functioning and allows better performance of the plant's photosynthesis.

Nutrient Mobilization

Cytokinins move nutrients around the plant. This hormone enables the re-radiation of nutrients from the older tissues to the growing points. This function is significant in the development and productivity of the plant.

Regulation of Apical Dominance

Cytokinins often act with auxins in controlling apical dominance, thereby affecting the development of lateral buds. Cytokinins can increase the strength of apical dominance in stems, possibly by reducing the export of auxin from these buds. This leads to increased branching and thus a more robust plant structure and yield.

Applications of Cytokinins

The applications of cytokinins is described below-

Agricultural Applications

Cytokinin is used in agriculture to increase crop production and plant growth. It forms an integral part of tissue culture and micro-propagation because, through it, tissue culture can develop into a young plant.

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