Ch 27: Plant Hormones

What are the 6 Major Groups of Hormones

Auxin

Cytokinins

Ethylene

Abscisic acid

Gibberellins

Brassinosteroids

Histroy of Auxin: Charles Dariwin and his son Francis

Found that plants bent toward the light (photoropism)

Where is Auxin found?

Found in shoot apical meristem

Role of Auxin

• Promotes Cell Elongation

• Promotes Apical dominance

• Promotes lateral/adventitious root growth

• Promotes Fruti growth

• Regulates tropisms

What do humans use Auxins for?

Promote rooting of cuttings and herbicides

Agent Orange was a

lethal auxin used to damage plants during vietnam war

Role of Cytokinin

• Promotes Cell Division

• Inhibits apical dominance

• Delays leaf senescene (aging)

Ration of Auxin and Cytokinin results

Both auxin and kinetin → undifferentiated cell division (cullus)

More Auixn → Roots formed

More kinetin → Buds formed

Role of Ethylene

Promotes Ripening

Promotes leaf, petal, and fruit abscission

Climacteric fruits vs non-anticlimacteric fruits

Climacteric = more ethylene (tomato, apples, pears)

Non-climactic = less ethylene (citrus, grapes, strawberries)

Role of Abscisic Acid

Inhibits growth

Closes stomata

Role of Gibberlins

Promotes cell division and elongation, can lead to bolting or more space ina fruit

Hastens seed germination

What happens if gibberlin is applied to strawberry

Seeds start germinating and grow on the fruit

Brassinosterioids

Responsible for developmental processess, steroid-based