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04 March 2010ECOL 182R UofA

K. E. Bonine

Plant Function

(Freeman Chs 38 & 39)

Videos34.3, 39.1browser

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18 Feb KB – Fungi, Ch31

23 Feb KB – Prokaryotes & Protists, Ch28&2925 Feb KB – Plant Diversity, Form, Function, Ch30&40

2 Mar KB – Plant Form and Function, Ch36&374 Mar KB – Plant Function, Ch38&39

9 Mar KB – Plant Ecology, Ch50,52,53 11 Mar KB – Ecology, Ch50,52,53

13-21 Mar Spring Break

23 Mar KB – Biology of the GalapagosWikelski 2000 and http://livinggalapagos.org/

25 Mar KB - Part 2. Discussion and Review.

30 Mar KB - EXAM 2

Lecture Schedule (middle third)

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Plants:Nutrition Etc.

Ch 38

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http://www.youtube.com/watch?v=ymnLpQNyI6g&feature=related

How do plants get nutrients they need?

Usually from soil through roots. A few interesting exceptions…

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In addition to carbon dioxide and water, plants require essential nutrients.

Most nutrients are available as ionsdissolved in soil water and are taken up by roots.

Nutrient absorption occurs via specialized proteins in plasma membranes of root cells. Most plants also obtain xxxxxxx or phosphorus from xxxxx associated with their roots.

Do Fungi Fix Nitrogen?

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Nutritional Requirements

• early 1600s, classic experiment by van Helmont

• mass of a growing plant comes from– soil?– water?– (elsewhere?)

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Hypothesis?

Predictions?

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Hypothesis?

Predictions?

RESULTS

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Nutritional Requirements

• early 1600s, classic experiment by van Helmont

• mass of a growing plant comes from soil?• mass of a growing plant comes from

water?

• [Most of the mass of the tree actually comes from xxxxxxxxxxx in the atmosphere] 10

Which Nutrients Are Essential?• An xxxxxxxx nutrient: required for

both normal growth and reproduction and for a specific structure or metabolic function.

• There are 17 essential nutrients for most vascular plants.

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Which Nutrients Are Essential?• Classified based on whether from water

&/or carbon dioxide versus from

• Essential nutrients available from H2O or CO2 are xxxxxxxxxxxxxxxxxxxx andxxxxxxxxxxxxx They make up 96% of the plant.

• Soil elements can be divided into macronutrients and micronutrients.

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• Macronutrients are the building blocks of nucleic acids, proteins, carbohydrates, phospholipids, and other key molecules required in relatively large quantities. They are

• nitrogen (N)• potassium (K)• calcium (Ca)• magnesium (Mg)• phosphorus (P)• sulfur (S).

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Which Nutrients Are Essential?

• Limiting nutrients are macronutrients that commonly act as limits on plant growth.

• xxxx andxx are often limiting nutrients.

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Which Nutrients Are Essential?

• Micronutrients are required in very small quantities. Rather than acting as components of macromolecules, they usually function as cofactors for specific enzymes. Examples include:

• iron, zinc, boron, copper, and nickel.

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studying nutritional deficiencies

• Hydroponic growth takes place in liquid cultures, without soil, so the availability of nutrients can be precisely controlled.

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Copper?

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Copper!

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Soil• Weathering—the forces applied

by rain, running water, and wind—begins the process of building soil from solid rock.

• Particles derived from rocks are the first ingredient in soil. As organisms occupy the substrate, they add dead cells and tissues. This organic matter is called xxxxx

• Organic + Inorganic = Mature Soil 20

Soil Formation Begins with Erosion of Rock

Soil texture is categorized by particle size:Gravel Sand

Silt Clay

(>2.0 mm) (0.02–2.0 mm)

(0.002–0.02 mm) (<0.002 mm)

Soil

Wind Freezing and thawing

Water (rain)

Organisms (plants, lichens,

moss, fungi, animals,bacteria, archaea)

Solid rock Particles

Particles

Particles

Particles

Soil formation begins when wind, temperature changes,rain, and organisms breaksmall particles off solid rock

Succession…

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What Factors Affect Nutrient Availability?

• + Cations + bind to soil particles• - Anions - stay in solution.

– (Leaching: loss of nutrients via washing).

• Soil pH (lower pH ~ more H+)

– acidic (low pH) or alkaline (high pH)22

What Factors Affect Nutrient Availability?

• Cations tend to bind to soil particles, while anions stay in solution.

• The loss of nutrients via washing is called leaching.

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Root Hairs Increase the Surface Area Available for Nutrient

Absorption

Zone of maturation

Root hairs

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Mechanisms of Nutrient Uptake• Plant cell walls can be permeable:

– to ions– small molecules– some large molecules

• Membrane proteins allow only specific ions to cross the plasma membrane: highly selective

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Establishing and Using a Proton Gradient

• Root-hair cells have proton pumps (H+-ATPases) in their plasma membranes that move nutrients into the cell against a strong concentration gradient.

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Ions Enter Roots along Electrochemical Gradients Created by

xxxxx Pumps

Outside cell (positive)

Root hair

Proton pump

Inside cell (negative)

Net negative charge

Net positive charge

Proton pumps establish an electrochemical gradient.

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Cations Enter Roots via xxxxxxxxxx

Proton pump

Cations enter root hairs via channels.

Channel

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Anions Enter Roots via xxxxxxxxxxxxxxx

Proton pump

Cotrans-porter

Anions enter root hairs via cotransporters.

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Cation vs Anion Nutrients• Anions easier to get than cations

– But anions can leach out of sandy soils– Anions better retained in clay soils

• Cations often bound to organic or inorganic soil particles

• Cation– H+ (proton) for Mg+ or K+ or Ca+ etc.– Plants facilitate by pumping H+ out of

root hairs30

CationH+ (proton) for Mg+ or K+ or Ca+ etc.

Plants facilitate by pumping H+ out of root hairs

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Nutrient Transfer via Mycorrhizal Fungi

• Vast majority of plants take up nutrients through their root hairs

• But, most need more nitrogen and phosphorus

• Help from fungi that live in close association with their roots.

• These fungi are called mycorrhizae

Review Fungi

lecture

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Photosynthetic products

Cross section of plant root

SoilFungal hypha

Plants provide sugars to

mycorrhizae

The hyphae secrete enzymes that digestmacromolecules. Thehyphae than absorbthe resulting ions

Mycorrhizaeprovide nutrientsto plants

mycorrhizaeprovide xxxxand/or phosphorus to the plants in exchange for sugar.

Symbioticmutualism

Review Fungi lecture

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In Salt-Tolerant Plants, an xxxxConcentrates Sodium in Vacuoles

In the tonoplast, antiporters send H+ out and Na+ in.

Pro

ton

gra

die

nt Antiporter

Protonpump

Cyt

op

las

mT

on

op

las

tIn

sid

e

vac

uo

le

Not all soil ions are “good” for the plant

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Some species of plant have specialized methods of obtaining nutrients, including associations with nitrogen-fixing bacteria,

parasitism, and carnivory.

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Nitrogen Fixation

• Plants and other eukaryotes cannot use N2 from the atmosphere.

• However, some xxxxxxx are able to absorb N2 from the atmosphere and convert it to ammonia, nitrates, and nitrites in a process called nitrogenfixation.

See prokar

yote

lecture!

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Nitrogen Fixation• Such bacteria often take up residence

inside plant root cells.

• For example, members of the bacterial genus Rhizobium associate with plants in the pea family (legumes).

• Rhizobia (Rhizobium species and close relatives) are found in nodules on the roots of legumes and provide the plant with

• ammonia in return for sugar and protection

See prokar

yote

lecture!

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Nodule in cross section

Nodules

Roots ofpea plant

In Some Plants, Roots Form Nodules where

Nitrogen-Fixing Bacteria Live

See prokar

yote

lecture!

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Nutritional Adaptations of Plants• Most plants use proton pumps as a

mechanism for importing nutrientsfrom the soil and/or acquire nutrients from symbioses.

• In addition, 99% of plants make their own sugars.

• Some plants don’t follow these rules, some appear to live on:

• 1) xxx some 2) xxxxxxx others, some catch 3)

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Epiphytic Plants• Epiphytes are plants that

are adapted to grow in the absence of xxxx. They often grow on leaves or branches of trees.

• They absorb most of the water and nutrients they need from rainwater, dust, and particles that collect in their tissues or in the crevices of bark. 40

Epiphytes Are Adapted to Grow in the Absence of Soil

Epiphytes grow on trees (e.g., Bromeliads).

Epiphytes

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Parasitic Plants

• Most parasitic plants make their own sugars through xxxxxxxxxxxx and tap into the vascular tissue of their hosts for water and essential nutrients.

• Some plant parasites are nonphotosynthetic and obtain all their nutrition from the host.

• There are at least 3000 species of parasitic plants 42

Some Plant Parasites Tap into the Xylem Tissue of Their Hosts

Mistletoe haustoria penetrate hostxylem and extract water and ions

Host tree

MistletoeHost xylem

Mistletoe

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Why are these all found in the same habitat?

BOGS

-Stagnant water-Low oxygen levels-Acidic-Nutrient poorxxxxxxxxxxxxx Slow

cranberries

‘mummies’

carnivores

peat

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Carnivorous Plants• Carnivorous plants use modified

leaves to trap insects and other animals, kill them, and absorb the prey’s nutrients.

• Carnivorous species make their own carbohydrates via photosynthesis but use carnivory to supplement the nitrogen available in the environment, which is often lacking. 46

Sundews Have Modified Leaves with a Sticky Surface That Catches Insects

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http://www.youtube.com/watch?v=ktIGVtKdgwo&NR=1&feature=fvwp

Venus fly trap - The Private Life of Plants - David Attenborough - BBC wildlife

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Plant Sensory Systems

(Freeman Ch39)

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Plant Sensory Systems, Signals, and Responses

Plants process informationEnvironmental stimuli affect ability

to grow and reproduce…• wavelength of light, photoperiod, time

of day• gravity, mechanical stimulation (touch

or wind)• disease-causing agents and herbivores. 50

Information Processing• Monitor aspects of environment that

affect fitness (survive & reproduce)

• Three steps:• (1) a receptor cell receives an

external signal• (2) the receptor cell sends a signal to

cells in another part of the plant• (3) responder cells receive the signal

and change activity appropriately.

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STEPS IN INFORMATION PROCESSING

External stimuluson receptor cell

Internalsignal

Cell-cellsignal

Internalsignal

1. Receptor cellperceives externalstimulus andtransduces theinformation to aninternal signal.

2. A hormone(cell-cell signal)released by thereceptor cell travelsthroughout the body.

3. Receptor cellsreceive the hormonal(cell-cell) signal,transduce it to aninternal signal, andchange activity.

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Signal Transduction• Signals from environment received by

specialized protein (for that function).

• Receptor proteins change shape in response to a stimulus. This causes the information to change form―from an external signal to an intracellular signal.

• This process is called

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Signal transduction in a receptor cell often results in the release

of a xxxxxxx that carries information to responder cells.

A few examples…

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When sensory cells receive a stimulus, they transduce the

signal and respond by producing hormones that carry

information to target cells elsewhere in the body.

Hormones produce a responseby acting on target cells.

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SIGNAL TRANSDUCTION

Cell wall1. Signal

2. Receptor protein changesin response to signal.

Cell membrane

3. Receptor or associated proteincatalyzes phosphorylation reaction.

ATP

ATP

ATP

ATP

ADP

ADP

ADP

ADP

4. Phosphorylatedprotein triggersphosphorylationcascade (left)…

…OR release ofsecond messenger(right).

Secondmessenger

Vacuole

5. Phosphorylatedproteins or secondmessenger initiateresponse.

Ph

osp

ho

ryla

tio

nca

scad

e

Nuclear envelope OR OR

DNA

6. Activate or represstranscription.

6. Activate or represstranslation.

Nucleus

6. Change ion flowthrough channel orpump.

Shoots bend specifically toward blue light.

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Blue Light:The Phototropic Response

• Plants sense and respond to specific, narrow range of wavelengths

• Any directed movement by an organism toward light is called xxxxxxxxx.

• Plants exhibit a phototropic response only to blue wavelengths

• Why blue light?

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Chlorophyll a and b Absorb Most Strongly in the Blue (and Red) Parts of the Visible Spectrum

Chlorophyll b

Chlorophyll aDifferent pigmentsabsorb differentwavelengths of light

Photosynthesis

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Auxin: Phototropic Hormone• The sensory and response cells in

phototropism are not the same. Blue light is sensed at the tip of a coleoptile(protected shoot) and info is then transmitted to lower cells.

• Auxin (a hormone) is produced at the tip of the coleoptile, is transported to the area of bending, and acts as a signal…

• Auxin promotes cell xxxxxxxx in the shoot.

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Photoperiodism & Flowering• Flowering in response to changes in day length—

triggered by red/far-red light.

• Photoperiodism is any response by an organism that is based on xxxxxxxxxx, the relative lengths of day and night.

• In plants, the ability to measure photoperiod is important because it allows the plant to respond to seasonal changes in climate and the correlated availability of resources and pollinators. 60

Different Species Respond to Photoperiod in Different Ways

How do plants respond to differences in day length?

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Youth, Maturity, and Aging: The Growth Responses

• Controlling growth in response to changes in age or environmental conditions (one of the most basic aspects of information processing in plants).

• Hormones play a key role in regulating

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Cytokinins & Cell Division

• Cytokinins are a group of plant hormones that promote cell division.

• Cytokinins are synthesized in root tips, young fruits, seeds, growing buds, and other developing organs.

• Cytokinins regulate growth by xxxxxxx the xxxxxx that keep the cell cycle going. In the absence of cytokinins, cells arrest at the G1 checkpoint in the cell cycle and cease growth.

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Cytokinins Affect the Cell CycleMitosis

M

G2DIVISION

S

G1

INTERPHASE

Cytokinins promoteexpression of genesthat start S phase (DNAsynthesis). Withoutcytokinins, cells remainin G1 and do not divide 64

Gibberellins and ABA: Growth and Dormancy

• Two types of hormones are responsible for initiating and terminating growth in plants in response to changes in environmental conditions:

• gibberellins xxxxxxx growth, abscissic acid (ABA) xxxxxxgrowth.

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Gibberellins Stimulate Shoot Elongation

• Gibberellic acid (GA) is a gibberellinthat appears to promote cell elongation and to increase rates of cell division in roots.

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Gibberellins and ABA Interact during xxxxxxxxxxxx and Germination

• Many plants produce seeds that have to undergo a period of drying or a period of cold, wet conditions before they are able to germinate in response to warm, wet conditions.

• In many plants, ABA is the signal that inhibits seed germination, and gibberellins are the signal that triggers embryonic development.

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Video 34.3 Germination of soybean plants

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• During seed germination, gibberellins activate production of a-amylase, a digestive enzyme that breaks the bonds between sugar units of starch. This releases sugars to the growing embryo.

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ABA Closes Guard Cells in Stomata

• In most plants, stomata open in response to blue light, allowing gas exchange during photosynthesis. When stomata are open, water can be lost; if the roots cannot replace water lost at the leaves, then the stomata close.

• ABA from xxxxxxxx is transported to leaves, resulting in the xxxxxxx of stomata. Therefore, this signal overrides that from the blue-light receptors.

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xxxxxx and Senescence

• Senescence = regulated aging process.

• The gaseous hormone ethylene is strongly associated with three aspects of senescence in plants: – 1) x– 2) flower fading– 3) abscission.

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The abscission zone is a region of the leaf

petiole that becomes more sensitive to

ethylene as auxin levels drop. As a result, it

degrades first and the leaf breaks off at this

point.

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Leaves Drop in Response to Signals from Auxin and Ethylene

LEAF SENESCENCE AND ABSCISSION

Healthy leaf

Abscission zone

Age, drought, temperature,day length, etc. reduceauxin production from leaf

Senescent leaf

1. High auxin: Cells in abscissionzone are insensitive to ethylene. Leaf functions normally.

2. Low auxin: Cells in abscissionzone become more sensitive toethylene, leading to leaf senescence.

Abscised leaf

3. Leaf detaches at theabscission zone.

A protective layer hasformed to seal stemwhere leaf was attached

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OverviewPlant Growth Regulators

(1) A single hormone often affects many different target tissues. This means there can be an array of responses to the same intercellular signal.(2) In most cases, several hormones affect the same response.

Hormones do not work independently―they xxxxxxx with each other. 74

Gravity: The GravitropicResponse

• xxxxxxxx is the ability of plants to move in response to gravity.Roots grow down and shoots grow up or out.

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Auxin as the GravitropicSignal

• Root cap cells that sense changes in the direction of gravitational pull respond by changing the distribution of auxin in the root tip.

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The AuxinRedistribution Hypothesis for Gravitropism

Auxindistribution

AUXIN AS THE GRAVITROPIC SIGNAL

Gra

vity

Auxin

1. Normal distributionof auxin in vertical rootprior to disturbance.

2. Root tip moved intohorizontal position.

3. Gravity-sensing cellsactively redistribute theauxin–more goes tobottom side.

4. Asymmetric auxindistribution inhibits cellgrowth on lower sideand stimulates growthon upper side, leadingto bending.

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Auxin's Overall Role• Auxin: controls growth via phototropism,

gravitropism, and apical dominance.

• Auxin has other important effects as well:

• Fruit development is influenced by auxinproduced by seeds within the fruit.

• Falling auxin concentrations are involved in xxxxxxxx (the shedding of leaves and fruits) associated with xxxxxxxxx (aging). 78

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How Do Plants Sense and Respond to Pathogens?

• If a pathogen invades a plant, the plant mounts a defense called the hypersensitive response (HR). HR causes the rapid and localized death of cells surrounding the site of infection, xxxxxx the pathogen.

• Other Responses too… 80

Video 39.1Lepidopteran larvae feeding on leaves

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Herbivory• xxxxxxxxxxxxxxxxxxx = toxins

(Primary metabolites involved in homeostasis and typical cellular function)

• Tobacco makes nicotine– Harmful to many herbivores

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Secondary Metabolites• Hormones/Pheromones

– Mimic juvenile hormone; stop molt to adult– Attract your herbivore’s insect prey!– Warn other plants to mobilize their

defensive cascades

• Poisons– Disrupt nervous system of herbivore

• nicotine– Disrupt digestive system of herbivore

• proteinase inhibitors

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How Do Plants Sense and Respond to Herbivore Attack?

• Many plant seeds and storage organs contain proteinase xxxxxxxx, proteins that block the enzymes found in the mouths and stomachs of animals that digest proteins.

• When a herbivore ingests a large dose of a proteinase inhibitor, it gets sick. As a result, herbivores learn to detect and avoid plant tissues containing high concentrations of these proteins.

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Pheromones Released from Plant Wounds Recruit Help from Wasps

• A xxxxxxxx is an organism that is free living as an adult but parasitic as a larva. Because parasitoids (for example, a wasp egg laid in a caterpillar's body) kill their host, parasitoid attacks limit the amount of damage that herbivores do to plants.

• Pheromones are chemical messengers synthesized by an individual and released into the environment that elicit a response from a different individual.

• Plants produce wasp attractant pheromones in response to attack by caterpillars.

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Parasitoidwasp

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Attract the herbivore’s xxxx!

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Secondary Metabolites

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Tannins

oak leaves

grapes/wine

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Milkweeds

Secrete a poisonous

latex

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Swallowtail butterflies incorporate milkweed toxins into their own tissues

for defense (via bird learning)

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Milkweeds Secrete a poisonous latex

Some herbivores ‘learn’ to disable the

defense (cut the latex supply lines, then eat the leaf!)

Another example of an92

Cyanide (CN)Cyanide is a very rapidly acting toxin(used by communes for suicide!).

In plants, CN is combined with sugar as a cyanogenic glycoside.

Precursors, stored in vacuoles , get together in cytosol if plant is damaged by wilting, crushing, or chewing.

More than 1000 plant species have cyanide in some form.

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Aspirin!• Salicylic Acid common in plants

– Well-studied in Willows (Salix)– Used to combat many pathogens

• (e.g., viruses)

• Methyl salicylate, a related compound– aka ‘oil of wintergreen’– Volatilizes to signal other plants

(~pheromone) to defend selves