1

Dynamic Plant

Plant Movements,

Hormones &

Defense Systems

Resurrection plant

Selaginella lepidophylla

A “Club moss,”

Lycophyta

*Lab Make-up option*

Weed Profile Project

Pick a common weed in Oregon and create a

1-5 min presentation describing it.

Find out information about:

1. Its Range

2. Origin

3. Control methods

4. Natural herbivores/pathogens?

5. Positive & negative affects of the weed in

Oregon

Adaptive Plants:

Respond to their

changing environment.

2

Outline

Introduction: ‘Growth’

Plant Hormones

Plant Responses

o Tropisms

o Nastic responses

o Phytochromes

o Photoperiod/Circadian Rhythms

o Dormancy

o Plant defense systems

Introduction Growth - Irreversible increase in mass due to division

and enlargement of cells

Determinate growth - Plant grows, stops growing and dies in

one season.

Indeterminate growth - Plant or parts of plant grow and

continue to be active for several to many years.

Differentiation - Cells develop different forms

adapted to specific functions.

Development - Coordination of growth and

differentiation of a single cell into tissues and

organs

Plant Hormones

What is a hormone?

> A chemical signal.

These chemicals are produced by cells in one

location that influence other cells

e.g. growth in another region of the organism.

Typically they are proteins or steroids, which

are lipid based.

3

First why is it important to know

about plant hormones?

Knowledge of plant hormones have allowed us to

improve and manipulate many of our horticultural

crops.

Do you like having produce/flowers on demand?

Potatoes year round

Tomatoes in your salad anytime

Roses in the winter time

Tour of the Plant Hormones

Giberellins Working on your seedlings right now!

Named after a fungus that produces it

(Gibberella fujikuroi)

Affects:

Germination

Sprouting of buds

Elongation of stems & leaves

Stimulates flowering

Affects the development of fruit Effect of gibberellins

on cabbage

Auxins

Made in:

Apical meristem of shoot system.

Move from tip downward.

Affects:

Cell elongation

Phototropism

Development of vascular tissue

Fruit development

Retards senescence in leaves & fruits

Several Forms:

Indoleacetic acid (IAA)

Phenylacetic acid (PAA)

4-chloroindoleacetic

acid (4-chloroIAA)

Indolebutyric acid

(IBA)

4

Cytokinins

Produced in root – moves to shoot

Affects:

Stimulates embryo development

Promotion of sprouting of lateral buds.

Development of chloroplasts

Stimulation of the onset of fruits

Stimulate plant metabolism

Delays the aging of plant parts especially leaves

Abscisic Acid

Produced in petiole (stalk of the leaf)

Affects:

Dropping of leaves

Growth inhibition – blocks protein synthesis

Common in fleshy fruits - Prevents seeds from germinating while still on plant

Induces dormancy in buds

Closing of stomata

Ethylene

Produced by ripening fruits

Affects:

Ripening of other fruits

Abscission of fruits &

leaves

Maturation of flowers

This is why bananas can be picked green and

sent to market from Central America to the U.S. to ripen.

Tomatoes, grapes and strawberries don’t respond to artificial ethylene exposure.

Ethylene from apple caused

abscission of holly leaves

5

Hijacked: Insect induced galls!

How do Plants Respond to

External Stimuli?

o Tropisms

o Nastic responses

o Phytochromes

o Photoperiod/Circadian Rhythms

o Dormancy

o Plant defense systems

Phototropism

6

Phototropism

Auxin migrates away from light, and

accumulates in greater amounts on opposite

side, promoting greater elongation of cells on

dark side.

Positive phototropism

Gravitropism

Gravity may be perceived by amyloplasts in

root cap, by proteins on outside of plasma

membrane, by whole protoplast, or by

mitochondria and dictyosomes.

Primary roots - Positively gravitropic

Shoots - Negatively gravitropic

Thigmotropism

7

Nastic Response:

http://www.youtube.com/watch?v=g0LFBM3hOLs

http://www.youtube.com/watch?v=O7eQKSf0LmY

• Plant response to external stimuli

• Mechanisms:

1. Cell enlargement/turgor movements

2. Cell division (mitosis)

• Examples:

1. Venus fly trap

2. Mimosa

Plant Movements: Turgor movements

“Sleep” movements - Circadian

rhythms

Regular daily cycles

Leaves or petals fold in regular daily

cycles.

Members of the legume family, prayer

plants

Turgor movements, and stimuli of light

and temperature involved.

Controlled by a biological “clock” on

approximately 24 hours cycles

Appear to be controlled internally Circadian rhythm

in prayer plant

How do plants detect light?

Phytochrome – a plant pigment that literally means

“plant color.”

Found in most plant organs, especially meristems.

An internal regulator.

This regulator helps seeds know it is appropriate to

germinate or not and if it is time to flower.

8

Importance of Phytochrome

Photoperiodic responses

Photomorphogenesis e.g. leaf expansion

Greening of the leaves

Germination of light sensitive plants e.g.

lettuce.

Types of Phytochrome

Pr (inactive phytochrome) – absorbs red light.

Absorption peak at 660 nm in EMS.

Pfr (active phtochrome) – absorbs far red light which

is “fully reactive.”

AP peak at 730 nm.*

Natural White light favors formation of Pfr.

> Makes the plant respond by becoming

green and lush.

When is Phytochrome Active?

Answer – all the time (it is the biological clock)

I. Pr converts to Pfr in daylight and the plant

grows lush.

II. Pfr converts to Pr when the plant is in the

shade and it grows spindly to try to find light.

9

Sensing Time

Photoperiod – The initiation of flowering and other vegetative activities in reponse to relative lengths of day & night.

Dormancy – Period of inactivity in some plant part, usually in response to environmental cues e.g. declining day length.

Quiescence – The state in which a seed cannot germinate unless environmental conditions normally required for growth are present. E.g. germination in desert seeds after rains occur.

Senescence – The breakdown of cell components and membranes that lead to death of cell e.g. dropping leaves in the fall.

Plant Defenses: Thorns Thorns: Modified stems

Examples:

Acacia

Crataegus (Hawthorn)

Giraffe Eating spiny acacia tree –

nevermind the thorns!

www.ecomtips.com/.../ giraffe_wnr-

4028c.jpg

Spines: Modified leaves

Examples: Opuntia spp.

Prickly pear cactus

Plant Defenses: Spines

10

Prickles: epidermal cells

Examples: Rosa spp.

Plant Defenses: Prickles

Plant Defenses: Trichomes

Trichomes: hairs

Can be glandular

Example: tomato

Plant Defenses: Trichomes

Glandular trichome of Stinging Nettle Urtica dioica

11

Plant Defenses: Sap/Latex

Milkweed: Asclepias spp

Milkweed beetle

Chemical Compounds

Plant Primary compounds – Molecules

necessary for normal growth and regulation.

Plant Secondary compounds – Molecules

that help ensure plant survival.

> Repellent

> Kill or damage predator

10,000+ compounds are toxic to animals.

Salicylates – help

plants detect and

respond to infection.

Willow family:

Salicaceae

Aspen (Populus)

Cottonwood

Willow (Salix)

Balsam poplar

12

‘Talking’ Trees!

“Stones have been known to move and trees to

speak”-- Shakespeare’s Macbeth

Willows (Salix spp) wounded by insects

produce an airborne chemical hydrocarbon

ethylene

Trees over 100 ft away sensed this and

produced proanthocyanidin (an insecticide)!

Research team: University of Washington in

Seattle, led by Professor David F. Rhoades

Dealing with Injury

Compartmentalization - Survival mechanism

1) saps

2) resins

3) pitch

Prevent invaders from spreading to other parts of the

plant.

Benefits to humans: Incense, rubber, pitch increases

thermal output of burning wood.

Lab This week:

Read Pages 39-50 in Lab manual

Pre-lab assignment: P. 45-46

Turn in at the beginning of lab

13

Diffusion

Diffusion: the movement of molecules

“down a concentration gradient”

From HIGH LOW concentration

NO ENERGY required

Diffusion: The Molecular Basis

Robert Brown

Brownian motion: Random

movement of particles

caused by inherent kinetic

energy

Movement is

RANDOM, not

directional

Diffusion and Osmosis

Water

Solute

(Solvent) Selectively Permeable

Membrane

14

Solution

Osmosis: Activity

‘cell’ Hypertonic

Solution

Osmosis: Activity

Hypotonic ‘cell’

Solution

Osmosis: Activity

Isotonic ‘cell’

15

Anim

al C

ell

Pla

nt

Cel

l

Isotonic Hypotonic Hypertonic

Osmosis: Plant and Animal Cells

Anim

al C

ell

Pla

nt

Cel

l

Isotonic Hypotonic Hypertonic

Osmosis: Plant and Animal Cells

Anim

al C

ell

Pla

nt

Cel

l

Isotonic Hypotonic Hypertonic

Osmosis: Plant and Animal Cells

16

Anim

al C

ell

Pla

nt

Cel

l

Isotonic Hypotonic Hypertonic

Osmosis: Plant and Animal Cells

Plasmolyzed Turgid