•Bonus #2 is due F 3/21

Today:

•Water Stress

and

•Genetically Modifying Plants

CB 36.13

Water moves from the ground through roots into the shoot and out stomata in the leaves.

CB 39.28

What happened to this root?

CB 39.28

Flooding, constant submersion… Why would the plant respond like this?

CB 36.7

Much of plant support comes from turgor pressure.

http://plantsinmotion.bio.indiana.edu/plantmotion/vegetative/veg.html (wilting)

CB 36.13

Water moves from the ground through roots into the shoot and out stomata in the leaves.

Stomata control entry of CO2 and exit of H2O from plant leaves

Stomata

CB 36.12

What about when water is scarce?

CB 36.16

Structural adaptations of a plant that grows in an arid environment

Oleander

CB 36.16

Structural adaptations of a plant that grows in an arid environment:

•Thick cuticle

•Thick epidermis

•Recessed stomata

Oleander

Stomata density can change depending on the environment. Typically ~200-300/mm2

Measurements of herbarium samples and present day samples have shown a 40% decrease in stomata over the last 200 years.

F. I. Woodward (18 June 1987) Nature 327, 617 - 618

Individual plants can change stomata number to adjust for changes in the environment.

Only mature leaves exposed to high CO2

New leaves develop with fewer stomata

JA Lake et al (10 May 2001) Nature 411, 154

CB 36.14

Stomata aperture is affected by many stimuli: light, water, temperature, sugar content, circadian rhythm, CO2 levels…

Photosynthesis is only efficient over certain temperature range. Transpiration cools plants.

CB 36.14

Stomata aperture is affected by many stimuli: light, water, temperature, sugar content, circadian rhythm, CO2 levels…

CB 36.15

Plants must integrate these various signals to determine an appropriate response

Human resource production and use

Worldwide Grain Production per Person

http://www.earth-policy.org/Indicators/Grain/2006.htm

http://www.earth-policy.org/Indicators/Grain/2006.htm

World Grain Stocks as Days of Consumption

~60 percent of the world grain harvest is consumed as food, ~36 percent as feed, and ~3 percent as fuel. While the use of grain for food and feed grows by roughly 1 percent per year, that used for fuel is growing by over 20 percent per year.

http://www.earth-policy.org/Indicators/Grain/2006.htm

from Teosinte MaizeBy artificial selection that began ~10,000 years ago.

Hunter-Gatherer

Agricultural

Industrial

Genetic Engineering: Direct manipulation of DNA

CB 20.2

We can now insert new genes or modify existing genes of plants

CB 20.2

Mil

lion

s of

Hec

tare

s

Texas =70 ha

Global area planted with GM crops

http://www.gmo-compass.org/eng/agri_biotechnology/gmo_planting/257.global_gm_planting_2006.html

Why Change a Plant’s DNA?

• Can change plant so that it has new or different characteristics

– Drought or other stress resistance– Produce needed protein

– Insect resistance (Bt toxin)

– Herbicide resistance (Round-up)

– Chemical remediation

Change is ever present…

precipitation changes

Irrigating crops eventually leads to increased soil salinity

Freshwater is not pure water. It contains many salts, such as: sodium 6mg/L; chloride 7mg/L; calcium 15mg/L; sulfate 11mg/L; silica 7mg/L; magnesium 4mg/L; and potassium 3mg/L

http://science.jrank.org/pages/2857/Freshwater.html

Why Change a Plant’s DNA?

• Can change plant so that it has new or different characteristics– Produce needed protein

– Insect resistance (Bt toxin)

– Herbicide resistance (Round-up)

– Drought or other stress resistance

– Chemical remediation

% o

f T

otal

US

Acr

esCommon GM Crops in the U.S.

http://blog.wired.com/

wiredscience/2007/09/

monsanto-is-hap.html

Herbicide Tolerance; Insect Resistance; Viral Resistance

Types of Genetically Modified Crops

Mil

lion

s of

Hec

tare

s

Texas =70 ha

Is genetically engineering plants a good idea?

http://www.gmo-compass.org/eng/agri_biotechnology/gmo_planting/257.global_gm_planting_2006.html