What is the Difference Between Auxin and Cytokinin

The main difference between auxin and cytokinin is that auxin is responsible for apical dominance, whereas cytokinin is responsible for cell division and differentiation. 

Auxin and cytokinin are two plant hormones that are chemicals that regulate the growth, development, and reproduction of plants. 

Key Areas Covered

1. What is Auxin
– Definition, Features, Function
2. What is Cytokinin
– Definition, Features, Function
3. Similarities Auxin and Cytokinin
– Outline of Common Features
4. Difference Between Auxin and Cytokinin
– Comparison of Key Differences

Key Terms 

Auxin, Cytokinin

What is Auxin

Auxin is a plant hormone responsible for the growth of the shoot. It is produced in the stem, buds, and root tips. The main form of auxin is indole 3-acetic acid (IAA). Auxin promotes differential growth concerning gravity and light. The movement of auxins to the darker side of the plant causes the cell elongation, curving the plant stem towards the light source. This movement of plants is called phototropism. Also, auxin promotes apical dominance by maintaining the dormancy of the axillary buds at the dormant stage. The apical dominance exists as long as the apical meristem produces auxins.

Figure 1: Phototropism

In addition, auxin promotes growth in shoot segments. It also promotes the development of roots. Auxins play a role in the development of the callus as well.

What is Cytokinin

Cytokinin is a plant hormone that promotes cell division or cytokinesis in shoots and roots. Therefore, it involves cell growth and differentiation. Also, it affects apical dominance, leaf senescence, and axillary bud growth. There are two types of cytokines: adenine-type cytokinins and phenyl-urea-type cytokinins. y kinetin, 6-benzyl amino purine, and zeatin are examples of adenine-type cytokinin, while diphenylurea and thidiazuron (TDZ) are phenyl-urea-type cytokinins. Mostly, roots synthesize adenine-type cytokinins. Cambium and other actively dividing tissues in plants produce cytokinin. However, plants do not produce phenyl-urea-type cytokinins.

Figure 2: Apical Dominance

Moreover, cytokinins are responsible for local and long-distance signaling. They are transported through the xylem. The primary functions of cytokinin are cell division and morphogenesis in shoots and roots. Also, it regulates apical dominance and axillary bud growth. According to the direct inhibition hypothesis, the effects of the two hormones: Auxin and cytokinin, are determined by the ratio of the two hormones. 

Similarities Between Auxin and Cytokinin

• Auxin and cytokinin are two plant hormones responsible for plant growth, development, and reproduction.
• They are also responsible for the longevity and death of plants.
• They are small molecules derived from secondary metabolism.
• Also, they adapt plants to environmental stimuli. 

Difference Between Auxin and Cytokinin

Definition

Auxin refers to a plant hormone that causes the elongation of cells in shoots and regulates plant growth. In contrast, cytokinin is a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots.

Production

Auxin is produced in the stem and root tip, while cytokinin is made in the xylem sap.

Function

Auxin promotes cell elongation in the apical bud, while cytokinin promotes cell division, enlargement, and elongation.

Role

Auxin promotes phototropism, hydrotropism, and geotropism, while cytokinin is responsible for lateral bud formation. 

Introduction

F. W. Went introduced auxin while Miller and Skoog isolated cytokinin. 

Conclusion

In brief, auxin and cytokinin are two plant hormones that regulate plant growth, development, and reproduction. Stem and root tip produce auxin. Auxin promotes cell elongation in apical buds. Also, it promotes phototropism, hydrotropism, and geotropism. In comparison, xylem sap produces cytokinin. It promotes cell division, enlargement, and elongation. Additionally, it promotes lateral bud formation. Therefore, the main difference between auxin and cytokinin is their production and function.   

References:

1. Encyclopædia Britannica, inc. (n.d.-b). Auxin. Encyclopædia Britannica. 
2. Cytokinin. Cytokinin – an overview | ScienceDirect Topics. (n.d.). 

Image Courtesy:

1. “Auxin Phototropism” By Patricklockwoood – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Apicale dominantie” By Snelleeddy – Own Work (CC-BY 2.5) via Commons Wikimedia