Phytohormones

Question 1

Phytohormone:

Answer 1

A substance synthesized in one plant organ that elicits a response in another

• endogenous: originates in plant (natural)
• exogenous: originates outside the plant

Question 2

Plant Growth Regulator

Answer 2

Organic substances that in small amounts promote, inhibit, or otherwise influence physiological processes

Question 3

Five main growth regulator classes

Answer 3

1. Auxins
2. Gibberellins
3. Cytokinins
4. Ethylne
5. Growth Inhibitors

Question 4

Auxins

Answer 4

Responsible for apical dominance in crops
- reason that new basal shoots sprout from tree stumps when tree is cut down
High rates of these materials result in unnatural stem growth and callus formation
Regulate cell division and expansion, stem elongation, leaf expansion, fruit development, and branching
Important in phototropism and geotropism
exs: to induce cuttings, to prevent fruit drop, to increase fruit set, to prevent sprouting of stored produce (potatoes)

Question 5

Gibberellins

Answer 5

Produced in shoot apex.
Occur in seed, flowers, germinating seed and developing flowers.
Promote cell division, stem elongation, seed germination (breaks dormancy), flowering, and fruit development.

Question 6

Cytokinins

Answer 6

Primarily promote cell division and lateral bud development.
Importance is germination to stimulate cell division of the embryo.
Important in leaf and stem expansion through promoting cell division
Sows senescence by preventing breakdown of chlorophyll in leaves

Question 7

Ethylene

Answer 7

involved in ripening of fruits

Question 8

Growth inhibitors include

Answer 8

Abscisic acid, phenolics benzoi acid, lactones

Question 9

Abscisic acid

Answer 9

Responsible for the formation of abscission layer in fruits and leaves of deciduous trees
Antagonistic to gibberellins and other growth-promoting hormones
Counteracts breaking of dormancy.
Also involved in stomatal closure