CH27: Hormones Flashcards
What are the 5 major categories of major hormone classes in plants?
- auxins
- Cytokinins
- Ethylene
- Abscisic acid
- Gibberellins
What are the minor hormones?
- salysilic acid
- jasmonic acid
- systemin
- florigen
What is a hormone?
A compound produced in one part of the organims that has significant impact of the reactions and processes in other parts of the organism (signaling molecule)
What is the first and most impartant hormone category?
Auxin
How to plants bend towards the light?
Differential cell elongation due to auxins
-as sun moves, the auxins will accumilate on the opposite side of the location of the sun (causes more growth on shade size, causing the overal plant to lean to the sun)
What does IAA stand for?
Indoleacetic acid
- smells like vinegar
What hormone category does IAA fall under?
Auxin
What does NAA stand for?
Naphthaleneacetic acid
- smells like mothballs
What hormone category does NAA fall under?
Auxin
Where are auxins produced?
The edges/margins of leaves or the stem tip
What direction does auxin transport?
Flows from top to bottom (down)
- does not come from the ground up, only top down
How to auxins flow between cells?
- By passive transport in IAAH (protonated) form
- By active transport via influx carrier (AUX1 protein) in IAA- (anion) form
What are the effects of auxin?
- Induces regeneration of xylem cells to reconnect the water conducting tubes when a plant is wounded
- Helps with fleshy fruit development
- plant bending towards light
What do cytokinins focus on?
Cytokinesis
How were cytokinins discovered?
First discovered in coconut milk (liquid endosperm)
How do you tell the difference between natural vs synthetic cytokinins?
Naturally occuring: Zeatin and i6 Ade (no additional rings)
Synthetic: an additional ring
Base rings are adenine
What does ABA stand for?
Abscisic Acid
What is ABA synthesized from?
Carotenoids
What are the functions of ABA?
- stomatal closing
- root to shoot signaling
- prevents seed gernimation and bud break (dormancy)
Where is ABA synthesized?
Mature leaves in roots, also in seeds (water stress stimulates production)
How does ABA move in leaves vs roots?
Leaves: via phloem
Roots: via xylem upwards
How do chloroplats (and other plastids) synthesize ABA?
Use terpenoid pathway
When the stoma is open, the guard cells are _____.
Turgid
When the stoma is closed, the guard cells are _____.
Flaccid
Why would the plant want to close stomata quickly?
To protect plant from water loss and pathogen entry.
What is the “shooting” hormone?
Cytokinins
What is the “rooting” hormone?
Auxins
What color are carotenoids?
Orange
What color are xanthophylls?
Yellow
What hormone helps with root to stem balance (not more than the other)?
Abscisic Acid (ABA)
Where is IAA NOT synthesized?
Roots
If the apical meristem of Phaseolus vulgaris is removed and auxin is applied to the cut surface, the growth of _____ is _____.
lateral buds; inhibited
When cultured tobacco stem tissues are treated with a combination of kinetin and IAA:
The cells divide rapidly
Where are high % of Gibberellins found?
In immature seeds
What do Gibberellins stimulate?
Cell division and cell elongation
What is the role of Giberellins?
- Breaking seed sormancy and germination
- cause flower bolting and affect fruit development
How do gibberellins cause dwarf “bush” beans to revert to their vining wild type?
Epigenetics - the giberellins “override” the swarf genetics
How do GA break dormancy in seeds?
Migrates from embryo to aleurone, stimulates enzymes, break down endosperm to start germination.
What hormone is involved with stomatal movement?
ABA
Studies on cucurbits have shown that, in this family:
Plants grown under short-day conditions evolve more ethylene than those grown under long day conditions.
Gibberellins overcome seed dormancy by:
stimulating cell elongation
Totipotency feres to the potential of:
A plant cell to give rise to an entire plant
Once a hormone binds to its receptor protein, THE NEXT event is that the receptor:
undergoes a conformational change
Patch clamp studies suggest that the IMMEDIATE effect of ABA in regulating stomatal movement is activation of _____in guard cells.
calcium channels
What are the effects of hormone ethylene?
- Fruit ripening (bananas, avo, apples)
- leaf and flower senescence
- leaf and fruit abscission
Define senescence.
The loss of a cell’s power to divide and grow.
Define abscission.
Detatchment of parts (falling off)
Ethylene transports by
Diffusion from site of synthesis due to being a gas
Where are cytokinins synthesized?
Root tips
Where is ethylene synthesized?
- most tissues in response to stress
- tissues undergoing senescence or ripening
