Plant Hormones

Auxin 

Auxin causes plant cell walls to become more flexible, which allows the cells to elongate as they grow. Auxin accumulates on the dark side of a stem. As a result, the cells on the dark side of a stem elongate more than the cells on the light side. The difference in elongation causes the stem to grow toward the light. Auxin also inhibits the growth of the buds along a stem. 

Abscisic Acid

• Induces seeds to synthesize storage proteins.
• Stimulates the closure of stomata (water stress brings about an increase in ABA synthesis). 
• Inhibits shoot growth but will not have as much affect on roots or may even promote growth of roots.  
• Inhibits the affect of gibberellins on stimulating de novo synthesis of a-amylase. 
• Has some effect on induction and maintanance of dormancy. 
• Induces gene transcription especially for proteinase inhibitors in response to wounding which may explain an apparent role in pathogen defense. 

Ethylene 

• Stimulates flower opening. 
• Stimulates fruit ripening.
• Stimulates the release of dormancy. 
• Stimulates shoot and root growth and differentiation (triple response) 
• May have a role in adventitious root formation. 
• Stimulates leaf and fruit abscission. 
• Stimulates Bromiliad flower induction. 
• Induction of femaleness in dioecious flowers. 
• Stimulates flower and leaf senescence.