Chapter 26 Flowering Plants: Control of - PowerPoint Presentation

Slide1

Chapter 26

Flowering Plants: Control of Growth ResponsesLecture Outline

1

Slide2

Outline

26.1 Plant Hormones26.2 Plant Responses

2

Slide3

26.1 Plant Hormones

Flowering plants respond to environmental stimuli such as:Light, gravity, carbon dioxide levels, pathogen infection, drought, and touch.Response leads to the survival of the species. The responses can be:Short term

Stomata open and close in response to light levels.Long termThe response to gravity causes downward growth of the root and the upward growth of the stem.

3

Slide4

Plant Hormones

Plants respond to environmental stimuli using signal transduction.B

inding of a molecular “signal” that initiates and amplifies a response.Receptors – proteins activated by a specific signal.Transduction pathway – a series of relay proteins or enzymes that amplify and transform the signal.Cellular response – the result of the transduction pathway Hormones

Enable

plant cells to communicate

Are synthesized in one part of the plant

Travel within phloem or from cell to cell in response to the appropriate

stimulus.

4

Slide5

Signal Transduction in Plants

5

Slide6

Plant Hormones

AuxinsProduced in shoot apical meristem.

Found in young leaves, flowers, and fruits.Apically produced auxin prevents the growth of axillary budsApical dominancePromotes growth of roots and fruitPrevents loss of leaves and fruitPromotes positive phototropism of stems

6

Slide7

Auxin

and Phototropism

8

Slide8

Plant Hormones

Stems bend because Auxin:Moves to the shady side of the plant when it is exposed to unidirectional light.

Binds to plasma membrane receptors.The complex leads to the activation of a proton pump.Activated proton pumps H+ out of cell.Cell wall loosens.Turgor pressure increases due to the entry of water.Cell enlarges.

8

Slide9

Expansion of the Cell Wall

10

Slide10

Plant Hormones

Gibberellins are growth-promoting hormones Gibberellins cause stem elongation

There are about 70 gibberellins Each differ slightly chemically The most common is gibberellic acid

10

Slide11

Gibberellins Cause Stem Elongation

12

Slide12

Plant Hormones

Cytokinins

Class of hormones that promote cell division.Found in dividing tissues of roots, in seeds, and in fruits.Have been used to prolong the life of flower cuttings as well as vegetables in storageAuxin and cytokinins interactprevent senescence (aging process)

12

Slide13

Interaction of Hormones

Auxin and cytokinins interact

14

Slide14

Plant Hormones

Abscisic acid (

ABA) is produced by any “green tissue” (tissue containing chloroplasts).Sometimes called the stress hormone.Initiates and maintains seed and bud dormancy.Brings about the closure of stomata.

14

Slide15

Dormancy and Winter Buds

Dormancy and Germination

16

Slide16

Abscisic

Acid Promotes Closure of Stomata

17

Slide17

Plant Hormones

Ethylene

Gas formed from the amino acid methionine. Effects of ethylene:AbscissionStimulates certain enzymes, such as cellulase, which helps cause leaf, fruit, or flower drop.Ripening of fruitsIncreases the activity of enzymes, such as

cellulase

, that soften fruits

It also promotes the activity of enzymes that produce the flavor and smell of ripened fruits.

Axillary bud inhibition

Suppression of stem and root elongation

17

Slide18

Ethylene and Abscission

19

Slide19

Ethylene and Fruit Ripening

20

Slide20

Arabidopsis Is a Model Organism

Arabidopsis thaliana

A small flowering plant related to cabbage and mustard plants.Has no commercial value.It has become a model organism for the study of plant molecular genetics, including signal transduction. It is small, so many hundreds of plants can be grown in a small amount of space. Generation time is short – 5-6 weeks until maturity.It normally self-pollinates, but it can easily be cross-pollinated. The number of base pairs in its DNA is relatively small.

20

Slide21

26.2 Plant Responses

TropismPlant growth toward or away from a unidirectional stimulusPositive tropism

is growth toward the stimulusNegative tropism is growth away from the stimulusGravitropism - movement in response to gravityPhototropism - movement in response to lightThigmotropism - movement in response to touch

21

Slide22

Plant Responses

GravitropismWhen a plant is placed on its side, the stem grows upward, opposite of the pull of gravity.

Stems with root caps grow downward.Response depends on sensors called statoliths.Auxin may be responsible for:Gravitropism of roots and shoots.

22

Slide23

Plant Responses

PhototropismPositive phototropism of stemsOccurs because cells on the shady side of the stem elongate due to the presence of auxinA pigment absorbing blue light initiates phototropism

23

Slide24

Plant Responses

ThigmotropismUnusual growth due to contact with solid objects.Coiling of tendrilsThigmomorphogenesis occurs when the entire plant responds to the presence of environmental stimuli.

WindRain

24

Slide25

Plant Responses

Nastic movements:Do not involve growth.

Are not dependent on the stimulus direction.Turgor movementsResult from touch, shaking, or thermal stimulation.Mimosa pudicaVenus flytrap

Sleep movements

:

Occur daily in response to light and dark changes.

Circadian rhythm

25

Slide26

26

Turgor Movement

Slide27

Circadian rhythms:

Biological rhythms with a 24-hour cycleTend to be persistentRhythm is maintained in the absence of environmental stimuli Caused by a biological clock

Plant Responses

27

Slide28

Plant Responses

Photoperiodism:P

hysiological response prompted by changes in day or night length.Influences flowering in some plants.Requires participation of a biological clock and a plant photoreceptor called phytochrome.Phytochrome is a blue-green leaf pigment that alternately exists in two forms.Phytochrome red (P

r

) is inactive

Phytochrome far-red (

P

fr

) is

active

28

Slide29

Conversion of forms allows a plant to detect photoperiod changes.

Also promotes seed germination and inhibits stem elongation.

29Phytochrome Conversion Cycle

Slide30

Phytochrome Control of Shoot Elongation

32

Slide31

33

Plant Responses

FloweringFlowering plants can be divided into three groups based on their flowering status.

Short-day plants

flower when the day length is shorter than a

critical length.

Long-day plants

flower when the day length is longer than a critical length.

Day-neutral plants

are not dependent on day length for flowering.

Some plants may require a specific sequence of day lengths in order to flower.

Slide32

Photoperiodism and Flowering

34

Slide33

Plant Responses

Responses to the biotic environment:Plants are always under attack by herbivores and parasites.

Physical and Chemical Defenses:Cuticle-covered epidermis and barkSecondary metabolitesTanninsAlkaloidsCyanogenic glycosidesWound responses – proteinase inhibitors and

systemin

Hypersensitive response (HR)

– initiates wound response and seals wounded area

Indirect defenses – prevent egg laying in insects

Mutualistic relationships with animals - acacia tree and acacia ant

33

Slide34

Plant Predators and Parasites

34

Slide35

Wound Response in Tomato

35