Difference Between Auxin and Gibberellin

The main difference between auxin and gibberellin is that the auxin promotes the growth of the shoot system whereas gibberellin promotes stem elongation, germination, and flowering. Furthermore, auxin plays a role in apical dominance whereas gibberellin has no role in apical dominance.  

Auxin and gibberellin are two types of phytohormones responsible for the elongation of cells in the shoot. The other types of phytohormones are cytokinin, abscisic acid, and ethylene.  

Key Areas Covered 

1. What is Auxin
     – Definition, Facts, Effects
2. What is Gibberellin
     – Definition, Facts, Effects
3. What are the Similarities Between Auxin and Gibberellin
     – Outline of Common Features
4. What is the Difference Between Auxin and Gibberellin
     – Comparison of Key Differences

Key Terms 

Auxin, Gibberellin, Growth of the Shoot, Phytohormones 

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 the indole 3-acetic acid (IAA). Auxin promotes differential growth with respect to gravity and light. The movement of auxins to the darker side of the plant causes the cell elongation in that side, curving the plant stem towards the light source. This movement of plants is called phototropism. Also, auxin promotes the apical dominance by maintaining the dormancy of the axiliary buds at the dormant stage. The apical dominance exists as long as the apical meristem produces auxins. 

Figure 1: Phototropism

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

What is Gibberellin 

Gibberellin is the other plant hormone that promotes the elongation of cells. It is produced at the tip of the stem. The first discovered type of gibberellin is gibberellic acid. However, gibberellin only promotes the growth of the intact shoot. It also enhances the development of leaves. Gibberellin stimulates the internode of the dwarf plants.  

Figure 2: Increased Internodal Space Due to Gibberellin

Gibberellin is responsible for the bolting of rosette plants and root crops. During seed germination, gibberellin replaces the need for cooling of seed known as vernalization, which accelerates flowering when planted. Gibberellin also helps to break the dormancy of seeds.  

Similarities Between Auxin and Gibberellin 

• Auxin and gibberellin are two types of phytohormones responsible for the growth of the shoot. 
• Small quantities of them are required by the effector organ. 
• Their production occurs in a certain part and they are translocated to the effector organ to evoke the physiological, biochemical or morphological responses. 

Difference Between Auxin and Gibberellin 

Definition 

Auxin refers to a plant hormone that is responsible for the elongation of cells in shoots, regulating the plant growth whereas gibberellin refers to a plant hormone that stimulates stem elongation, germination, and flowering. 

Found in 

The auxin is found in higher plants while gibberellin is found in some higher plants and fungi. 

Structure 

Furthermore, the auxin is a double or single unsaturated structure with a side chain while the gibberellin consists of a mostly saturated tetracyclic gibbane structure without a side chain. 

Transport 

Also, auxin shows basipetal transport while gibberellin shows both basipetal and acropetal transport. 

Function 

Moreover, auxin is responsible for cell division, cellular expansion, cell differentiation, axial elongation, lateral expansion, and isodiametric expansion in plants whereas gibberellin is responsible for stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence.  

Shoot Growth 

In addition, auxin can promote the growth of shoot segments while gibberellin only promotes the growth of the intact shoot. 

Leaf Growth 

Also, the auxin has a little effect on leaf growth while the gibberellin enhances leaf growth. 

Apical dominance 

Auxin leads to apical dominance while gibberellin does not cause apical dominance. 

Conclusion 

Auxin is the main plant hormone responsible for the growth of the shoot. It mainly induces cell division and cell elongation. On the other hand, gibberellin is another plant hormone that has a role in seed germination and flowering apart from cell elongation. The main difference between auxin and gibberellin is the structure and function of each plant hormone.   

Reference:

1. Ersek, Kaitlyn. “What Are Plant Auxins? And How Do They Affect Plant Growth?” HOLGANIX Soil Nourishing Root Stimulating, Available Here
2. Davière, Jean-Michel, and Patrick Achard. “Gibberellin Signaling in Plants.” DEVELOPMENT AT A GLANCE, The Company of Biologists Ltd, 15 Mar. 2013, Available Here

Image Courtesy:

1. “Phototropism Diagram” By MacKhayman – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2. “Gib sprout” By MajorVariola – My own photograph. Releasing unconditionally. (Public Domain) via Commons Wikimedia