Ch. 39 Plant Responses to Ch. 39 Plant Responses to Internal and External Internal and External SignalsSignals

Objectives:

LO 2.29 The student can create representations and models to describe immune responses.LO 2.30 The student can create representations or models to describe nonspecific immune defenses in plants and animals.LO 2.35 TSIAT design a plan for collecting data to support the scientific claim that the timing and coordination of physiological events involve regulation.LO 2.36 TSIAT justify scientific claims with evidence to show how timing and coordination of physiological events involve regulation.LO 2.37 TSIAT connect concepts that describe mechanisms that regulate the timing and coordination of physiological events.LO 2.38 TSIAT analyze data to support the claim that responses to information and communication of information affect natural selection.LO 2.39 TSIAT justify scientific claims, using evidence, to describe how timing and coordination of behavioral events in organisms are regulated by several mechanisms.LO 2.40 TSIAT connect concepts in and across domain(s) to predict how environmental factors affect responses to information and change behavior.

OverviewOverviewSince plants cannot move (away from

threats or toward a resource) they respond to cues by adjusting their individual patterns of growth and development.◦Ex: opening of flowers for pollinator when

they are active.

39.1 Signal Transduction 39.1 Signal Transduction Pathways Link Signal Pathways Link Signal Reception to ResponseReception to Response

Etiolation: morphological adaptations for growing in the dark.◦Ex: a potato puts its resources into producing

stems because it is located under the soil. When exposed to light, the stem stops growing and

leaves with chlorophyll are produced (de-eiolation)

(a) Before exposure to light(b)After a week’s exposureto natural daylight

ReceptionPhytochrome receptors in the cytoplasm of

plants.

TransductionPhytochrome:

◦ opens Ca2+ channels (increases its concentration)

◦ changes shape activating cyclic GMP(These are second messengers relay and amplify the

signal to response proteins)

ResponsePost-translational – activates preexisting

enzymesTranscriptional – increases mRNA synthesis

Figure 39.4-3Figure 39.4-3

Reception 2 31 Transduction Response

CYTOPLASM

Plasmamembrane

Phytochrome

Cellwall

Light

cGMP

Secondmessenger

Ca2

Ca2 channel

Proteinkinase 1

Proteinkinase 2

Transcriptionfactor 1

Transcriptionfactor 2

NUCLEUS

Transcription

Translation

De-etiolation(greening)

response proteins

P

P

39.2 Plant Hormones Help Coordinate 39.2 Plant Hormones Help Coordinate Growth, Development, and Response to Growth, Development, and Response to StimuliStimuliThe discovery of plant hormonesTropism: growth response toward or away

from a stimulus.◦ Ex: plants grow toward light (phototropism)

(Darwins) A hormone is produced in the coleoptile that is transmitted down the stem to have cells facing the light slow growth and cells not facing the light grow faster.

Control

Light

Shaded side

Illuminatedside

Boysen-Jensen

Light

Light

Darwin and Darwin

Gelatin(permeable)

Mica(impermeable)

Tipremoved

Opaquecap

Trans-parentcap

Opaqueshield overcurvature

RESULTS

Frits Went placed the coleoptile tip on agar.

The agar contained a hormone.

When placed on one side of the plant, that side began to grow causing it to bend.

Auxin (indoleacetic acid) is the hormone produced which causes cell elongation (a plant growth hormone).

Control

RESULTS

Excised tip onagar cube

Growth-promotingchemical diffusesinto agar cube

Control(agar cubelackingchemical)

Offsetcubes

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Video: Phototropism

Hormone Where produced/found

Major Functions

Auxin Shoot apical meristems and young leaves

Stimulates stem elongation

Cytokinins Roots Regulate cell division

Gibberellins Meristems of buds and roots

Stimulates stem elongation, reproduction

Brassinosteroids All tissue Promote cell expansion

Abscisic acid (ABA)

All tissue Inhibits growth

Strigolactones Roots Promote seed germination

Ethylene All tissue Promotes ripening of fruits

39.3 Responses to Light Are 39.3 Responses to Light Are Critical For Plant SuccessCritical For Plant SuccessBlue-Light Photoreceptors

◦Phototropism◦Opening stomata◦Slowing hypocotyl growth once

seedling breaks ground.

(b) Coleoptiles before and after light exposures

Light

Time 0 min

Time 90 min

Phytochormes as Photoreceptors◦Protein which absorb red light which

stimulates germination.◦Discovered by exposing seeds to

different colors of light then observing them.

RESULTS

Red Red

Red Red Red Red

Far-red

Far-redFar-redFar-red

Dark (control)

Dark Dark

Dark

◦Phytochromes also serves as a shade avoidance indicator.

◦When in shade, far-red light is more abundant leaving the protein “inactive.”

◦This tells the plant it is in shade and needs to grow taller.

Synthesis

Pr Pfr

Red light

Far-red light

Slow conversionin darkness(some plants)

Responses:seedgermination,control offlowering, etc.

Enzymaticdestruction

Biological Clocks and Biological Clocks and Circadian RhythmsCircadian RhythmsCircadian rhythms are cycles that

occur every 24 hours which are not directly controlled by any known environmental variable.◦Putting plants in a controlled

environment (24 hours of light) only slightly get the rhythm off course (21-26 hour rhythms).

Noon Midnight

PhotoperiodismPhotoperiodismA physical response

to the relative lengths of night and day.◦Night time

requirements not to be broken by light or flowering won’t occur.

◦Ex: short day plants need uninterrupted long nights to flower (Long-night plants)

24 hours

Light Flashoflight

Darkness

Criticaldark period

Flashof light

(b) Long-day(short-night) plant

(a) Short day(long-night) plant

39.4 Plants Respond to a 39.4 Plants Respond to a Wide Variety of Stimuli Other Wide Variety of Stimuli Other Than LightThan LightGravity (gravitropism)

◦ Positive = downward growth of roots◦ Negative = upward growth of shoots◦ Detected by statoliths (cytoplasmic components

that settle to the bottom of the cell).

Statoliths 20 m

(a) Primary root of maizebending gravitropically(LMs)

(b) Statoliths settling tothe lowest sides ofroot cap cells (LMs)

© 2011 Pearson Education, Inc.

Video: Gravitropism

Mechanical Stimuli (being “touched”)◦Thigmomorphogensis are changes in

the form of a plant due to mechanical stimuli (wind, touch, water, etc)

(a) Unstimulated state (b) Stimulated state

© 2011 Pearson Education, Inc.

Video: Mimosa Leaf

Environmental Stresses Environmental Stresses (abiotic)(abiotic)Drought

◦ Plants lose water by transpiration and cannot replenish it.

◦ Responses: shed leaves, curl leaves, close stomata, root growth

Flooding◦ suffocates roots/no oxygen

Salt◦ Loss of water in soil◦ Toxic to plants

Heat◦ Denatures enzymes

Cold◦ Loss of fluidity of cell membranes slowing/stopping

transport in/out of cell.

39.5 Plants Respond to 39.5 Plants Respond to Attacks by Herbivores and Attacks by Herbivores and PathogensPathogensDefense against herbivores

◦ Physical defenses Thorns

◦ Chemical defenses Distasteful or toxic compounds Canavanine (replaces arginine when ingested) Attraction of parasitoid wasps

Wounding

Signal transductionpathway

Chemicalin saliva

Synthesisand releaseof volatileattractants

Recruitment ofparasitoid waspsthat lay their eggswithin caterpillars

2

1 13

4

Defense against pathogens◦ First line of defense is

the epidermis and periderm of plant body.

◦ Plants can recognize pathogen-derived molecules (effectors) causing the plant to either respond defensively or be taken over by the pathogen.

◦ The Hypersensitivity Response cells near infection site

secrete toxins then die to prevent the spread of infection.

R protein

Avr effector protein

R-Avr recognition andhypersensitive response

Infected tobacco leaf with lesions

Signal

Hypersensitiveresponse

Avirulentpathogen

Signal transduction pathway2

4

3

1

Systemic Acquired Resistance◦ General response putting whole plant “on alert”◦ Production of salicyclic acid in areas away from

infection, activating a signal transduction pathway to produce pathogenesis-related (PR) proteins

Systemic acquiredresistance

R protein

Avr effector protein

R-Avr recognition andhypersensitive response

Signal

Hypersensitiveresponse

Signaltransduction

pathway

Acquired resistance

Avirulentpathogen

Signal transduction pathway2

4

3

5

1

7

6