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

The two types of cytokinins are:

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.

Delay of Leaf Senescence

These hormones delay 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. It 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.

Interaction with Other Plant Hormones

The interaction between cytokinin and other plant hormone includes:

Agricultural and Horticultural Applications of Cytokinins

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.

Importance of Cytokinins in Plant Growth and Development

The importance of cytokinins in plant growth and development are:

• Maintain balance between root and shoot growth.

• Enhance photosynthesis and protein synthesis.

• Promote chloroplast development and leaf longevity.

• Support seed and fruit development through nutrient reallocation.

Cytokinins NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Functions of Cytokinin in Plants

• Interaction with other plant hormones

Practice Questions for NEET

Q1. You are given a tissue with its potential for differentiation in an artificial culture. Which of the following pairs of hormones would you add to the medium to secure shoots as well as roots?

1. IAA and gibberellin

2. Auxin and cytokinin

3. Auxin and abscisic acid

4. Gibberellin and abscisic acid

Correct answer: 2) Auxin and cytokinin

Explanation:

Functions of Cytokinins -

1. Cell Division:

• Cytokinins are essential for cytokinesis though chromosome dou­bling can occur in their absence.

• In the presence of auxin, cytokinins bring about division even in permanent cells.

• Cell division in callus (unorganized, undifferentiated irregular mass of dividing cells in tissue culture) is found to require both hormones.

2. Cell Elongation and Differentiation:

• Like auxin and gibberellins, cytokinins also cause cell elongation.

• Both auxin and cytokinins are essential for morphogenesis or dif­ferentiation of tissues and organs.

• Buds develop when cytokinins are in excess while roots are formed when their ratios are reversed.

• Cytokinins induce the formation of new leaves, chloroplasts in leaves, lateral shoot formation, and adventitious shoot formation.

• They also bring about lignification and differentiation of interfascicular cambium.

- Auxin and cytokinin ratio plays an important role in root and shoots growth.

Hence, the correct answer is option 2) Auxin and cytokinin.

Q2. Who demonstrated, for the first time, that plants could be grown to maturity in a defined nutrient solution in the complete absence of soil

1. Arnold Hoagland

2. Steward

3. Julius von Sachs

4. De saussure

Correct answer: 3) Julius von Sachs

Explanation:

It was only in 1860 that German botanist Julius von Sachs demonstrated the possibility of cultivating plants to maturity in a nutrient solution defined in the absence of soil. From this pioneering work, hydroponics has developed as a kind of soilless cultivation that takes support from nutrient solutions. His experiments provided an added impetus to the understanding of plant nutrition and physiology, which significantly modified present-day agricultural practices.

Hence the correct answer is option 3) Julius von Sachs.

Q3. The first cytokinin was discovered by

1. Charles Darwin

2. Osborne and Black

3. Miller, Skoog and Strong

4. Letham

Correct answer: 3) Miller, Skoog and Strong

Explanation:

The first cytokinin was discovered in 1955 by Miller, Skoog, and Strong during callus tissue culture experiments with tobacco. They identified a compound, later named kinetin, which promoted cell division in plant tissues. This discovery marked a significant breakthrough in plant biology, as cytokinins were recognized as a key group of plant hormones involved in regulating cell division, growth, and development.

Hence, the correct answer is option 3) Miller, Skoog, and Strong.

Also Used:

• MCQs on Structure, Function and Uses of Cytokinin

• Auxin Bioassay

• Photoperiodism, Vernalisation And Seed Dormancy

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