Difference between Auxin and Gibberellin

Phytohormone is an organic substance other than nutrients active in minute quantity which is formed in certain parts of a plant and is then usually translocated to some other parts or sites where it evokes physiological, biochemical and /or morphological responses.

Phytohormones are divided into  five groups: Auxin, Cytokininis, Gibberllins, Abscisic acid (ABA), and ethylene.

Auxin is earliest known plant growth regulator. It promotes cell elongation especially in shoots. It obtained from plant are called natural auxin.

Gibberellin: Kurosawa first time noted the existence of gibbellins in a fungus Gibberella fuzikuroi of ascomycetes infected rice plant. This is popularly known as Bakanne disease of rice.

Auxins vs Gibberellin

Auxins	Gibberellin
They are mostly found in higher plants.	They are mostly found in fungi and few higher palnts.
Structure: It has a double or single unsaturated ring structure. A Side chain is present.	It has tetracyclic gibbane structure. Unsaturation is comparatively less. A side chain is absent.
Auxin promotes growth in shoot segments.	Gibberllin promotes growth in intact shoot.
There is little effect on leaf growth.	Leaf growth is enhanced.
Auxin has no effect on genetically dwarf plants.	It enhances internode growth in genetically dwarf plants.
It causes apical dominance.	Apical dominance* is not affected.
It does not cause bolting in rosette plants and root crops.	It bring about elongation of stem or bolting in rosette plants and root crops.
It has no influence on the requirement of vernalization.	Gibberellin can replace the requirement of vernalization in most plants.
It has no effect on the flowering of long day plants.	It can replace the  requirement of long photoperiods in long day plants.
It is essential for the growth and formation of callus.	It does not influence formation and growth of callus.
It promotes rooting on cuttings.	It has no effect on rooting of cuttings.
It does not break dormancy.	It helps in breaking dormancy.
Auxin transport is polar.	It shows channel transport in different directions.
Root  growth is promoted by low concentration of auxin and inhabited by its normal concentration.	Gibbellin has no specific effect on root growth.
It does not produce hydrolysing enzymes for mobilizing food reserve during seed germination.	Gibbellin produces hydrolysing enzymes for solubilisation of food reserve during seed germination.

Apical dominance: promoting  apical bud growth and inhibiting lateral bud growth

Vernalization: cold treatment of seedlings to enhance flowering and fruiting