1. Plant hormones What is a hormone? How do they work?
Where are they formed?
What do they do?
Other plant responses…
Refer to chapter 26 in text.

2. What is a hormone?
A hormone (from Greek ὁρμή, "impetus") is a chemical released by a cell, a gland, or an organ in one part of the body that affects cells in other parts of the organism. Generally, only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one cell to another. (Wikipedia, if you couldn’t tell)
What hormones do you recall?
In animals?
In plants?
What are they made of?

3. What do you recall about how (protein) hormones work?
How do they work?
What do you recall about how (protein) hormones work?
signal transduction pathway
- Hormone’s message is amplified
at each step.
← Simplified version.
More realistic version. ↓

4. Where are they formed? In humans, formed in glands:
In plants, formed in dividing tissues:
… so also in growing leaves and fruit.
Where do they go?
Everywhere.

5. Auxins What do you recall of these guys from “stems” and “roots”?
(Phototropism? Gravitropism?)
Source: apical meristems
Effects: apical dominance, rooting, fruit growth
breaks cellulose for cell extension in phototropism
halts abscission and fruit dropping
Application: e.g. seedless tomatoes, agent orange

6. Auxins cont. Auxin efflux pump: In apoplasty (outside cells),
auxins are non-polar,
so can enter neighboring cells. ←
Inside cells,
auxins are negatively charged,
thus depending on permission,
(opening of transport pumps)
to exit the cell.
This is how the auxin gradient
across plant tissues
is established.
What controls these passages?
(under ongoing investigation)

7. Cytokinins What do you recall of these guys from the cell cycle?
(Three stop points..?)
Same thing here.
Source: actively dividing roots; also seeds and fruit
Effects: with auxins, or else callus forms
prevent senescence (sleep/death)
Application: increase axillary growth

8. Gibberellins What do you recall of these guys from germination?
(After imbibition? Prompts amylase production?)
That’s not all...
Source: young leaves, roots, embryos, seeds and fruit
Effects: stem elongation, increased growth
breaking dormancy
Application: increase size of flowers and plants
produce seedless grapes

9. Abscisic Acid (ABA) What do you recall of these from transport
and … OK, ecology?
(influences guard cells to close,
and It turns out it doesn’t usually cause abscission)
Source: “green” tissue, monocot endosperm and roots
Effects: increases dormancy, encases buds, closes stomata
Application: slow grape maturation, reduce desiccation stress

10. Ethylene What do you recall of this… from anywhere?
We haven’t hit it until now.
Source: especially fruit and apical meristems
Effects: reduces axillary buds, increases cellulase to
hasten ripening and abscission,
reduces chlorophyll (hence intensifying fruit color)
Application: GMO fruit (tomatoes) to not generate ethylene,
so they don’t ripen en-route, and then they’re
gassed at the store.

11. This is a simplified recap of the preceding slides:
The url at the bottom includes a BioNinja lesson on plant hormones.

12. (Why would a plant catch bugs?)
Other Plant Responses
nastic movement:
using turgor, e.g.
to fold leaves ↓
epidermis: →
1st line of defense
iopscience.iop.org 
(Why would a plant catch bugs?)
2o metabolites (by products): →
tannins, cyanogens, and
alkaloids (morphine, nicotine, caffeine)
for defense

13. Other Plant Responses cont.
hypersensitive response or HR:
pathogen walled off,
like innate immunity.
systematic acquired resistance or SAR:
immunity against encountered pathogens,
like acquired immunity.
(a bit of grazing helps plants)
faculty.uca.edu 

14. hormone
signal transduction pathway
auxins
auxin efflux pump
cytokinins
gibberellins
abscisic acid
ABA
ethylene
nastic movement
epidermis
2o metabolites
hypersensitive response HR
systematic acquired resistance
SAR