Plant hormones What is a hormone? How do they work?

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.

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?In animals?

In plants?

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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. ↓

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&docid=fNevLSLeaBGYNM&tbnid=qZeiCiFQi7OgfM:&ved=0CAQQjB0&url=http%3A%2F%2Fmigration.wordpress.com%2F2007%2F08%2F25%2Fbasic-concepts-signal-transduction%2F&ei=x90ZUvjlGeLk2AWCpoHoCg&bvm=bv.51156542,d.b2I&psig=AFQjCNEL70hlKRfVRIp10HMRM4K-VkuW5A&ust=1377513283732384

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.

Auxins

Source: apical meristemsEffects: apical dominance, rooting, fruit growth

breaks cellulose for cell extension in phototropism halts abscission and fruit dropping

Application: e.g. seedless tomatoes, agent orange

What do you recall of these guys from “stems” and “roots”?(Phototropism? Gravitropism?)

http://edscitutors.co.uk/blog/2012/03/higher-biology-revision-phototropism-in-plants/

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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)

http://home.earthlink.net/~dayvdanls/A

uxinTranspt.gif

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 fruitEffects: with auxins, or else callus forms

prevent senescence (sleep/death)Application: increase axillary growth

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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 fruitEffects: stem elongation, increased growth

breaking dormancyApplication: increase size of flowers and plants

produce seedless grapes

http://botanyprofessor.blogspot.com/2013_01_01_archive.htm

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Abscisic Acid (ABA)

What do you recall of these from transportand … OK, ecology?(influences guard cells to close, and It turns out it doesn’t usually cause abscission)

Source: “green” tissue, monocot endosperm and rootsEffects: increases dormancy, encases buds, closes stomataApplication: slow grape maturation, reduce desiccation stress

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Ethylene What do you recall of this… from anywhere?We haven’t hit it until now.

Source: especially fruit and apical meristemsEffects: 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’regassed at the store.

http://www.vce.bioninja.com.au/aos-2-detecting-and-respond/coordination--regulation/plant-hormones.html

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

Other Plant Responses

nastic movement: using turgor, e.g. to fold leaves ↓ epidermis: →

1st line of defense

2o metabolites (by products): →tannins, cyanogens, andalkaloids (morphine, nicotine, caffeine)for defense

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(Why would a plant catch bugs?)

Other Plant Responses cont.

systematic acquired resistance or SAR:immunity against encountered pathogens,like acquired immunity.

(a bit of grazing helps plants)

hypersensitive response or HR:pathogen walled off,like innate immunity.

faculty.uca.edu  www.udel.edu 

hormonesignal transduction pathway auxinsauxin efflux pumpcytokininsgibberellinsabscisic acid ABAethylenenastic movementepidermis2o metabolites hypersensitive response HRsystematic acquired resistance SAR