plant growth regulators - wikispacesgrowth+regulators... · some plant growth regulators ......

Plant Growth Regulators

Unit: Plant Science

Problem Area: Examining Plant Growth

Lesson: Plant Growth Regulators

� Student Learning Objectives. Instruction in this lesson should result in studentsachieving the following objectives:

1 Define plant growth regulator, identify the classes of regulators and describe

their functions.

2 Define tropism and examine the types of tropisms.

3 List examples of synthetic growth regulators and discuss how and why they

are used.

4 Describe commercial uses of plant growth regulators.

� List of Resources. The following resources may be useful in teaching this lesson:

Corresponding E-unit(s). Danville, IL: CAERT, Inc. www.mycaert.com

� List of Equipment, Tools, Supplies, and Facilities

� Copies of sample test

� Visuals from accompanying masters

� Copies of student lab sheets


� www.MYcaert.com

Copyright © by CAERT, Inc. | Reproduction by subscription only. | L040214

� Terms. The following terms are presented in this lesson (shown in bold italics):

� Interest Approach. Use an interest approach that will prepare the students for thelesson. Teachers often develop approaches for their unique class and student situations. Apossible approach is included here.

Several days before the introduction of this lesson prepare two identical plantsfor an interest approach. Select an upright growing potted herbaceous plantsuch as a coleus or tomato. Lay one of the two plants on its side. The plant onits side will curve upward in response to gravity. Present the two plants to theclass and ask a series of questions. Ask the students why the one plant iscurved. Is there an advantage to the plant for responding in this way? Is there aterm used to describe the plant response? What caused it to curve?

SUMMARY OF CONTENT AND

TEACHING STRATEGIES

Objective 1: Define plant growth regulator, identify the classes of regulators anddescribe their functions.

Anticipated Problem: What are plant growth regulators and what are their functions?

I. Plant growth regulators (PGR) are chemicals which affect the plant in manycomplex ways. They promote growth, inhibit growth, and modify growth anddevelopment. They can control such activities as cell division and differentiation, rootand shoot growth, flowering, and ripening. Plant growth regulators may be naturallyoccurring and manufactured in a plant or they may be synthetic, man-madechemicals.

A. Naturally occurring chemicals that regulate all growth and development of plantsare called plant hormones. Hormones are moved around the plant in extremelylow concentrations. Five different hormones are auxins, gibberellins, cytokinins,ethylene, and abscisic acid.

1. Auxins consist of a group of hormones that have a primary role in promotingcell elongation. The primary auxin is indoleacetic acid (IAA). Plants produce


� www.MYcaert.com


� abscisic acid

� apical dominance

� auxins

� cytokinins

� ethylene

� etiolation

� gibberellins

� gravitropism

� growth retardants

� indoleacetic acid (IAA)

� indolebutyric acid (IBA)

� naphthaleneaceticacid (NAA)

� phototropism

� plant growth regulators

� plant hormones

� synthetic growthregulators

� thigmotropism

� tropism

auxins in the apical meristem. They migrate down the stem moving throughone cell to the next rather than being transported through the phloem orxylem. Auxins have the greatest influence on cells closest to the apicalmeristem. The higher concentrations of auxins give the apical meristem domi-nance over growth below. Apical dominance is a term used to describe theapical bud’s dominance over the lateral buds.

2. Gibberellins induce cell elongation and cell division. They are produced instem and root apical meristems, seed embryos, and young leaves. Gibberellinsplay a key role in the development of flowers and in the production of enzymesduring seed germination.

3. Cytokinins are hormones responsible for cell division and differentiation. Theyare produced in the roots and transported throughout the plant via the xylem.Cytokinins encourage the growth of lateral shoots. They inhibit the branching ofthe roots. As an ingredient in tissue culture medium, cytokinins are an impor-tant promoter of cell division.

4. Ethylene is a colorless gas that speeds the aging of plant parts, particularlyfruit. It is produced in stems, ripening fruit, and dying leaves.

5. Abscisic acid is a growth-inhibiting hormone largely responsible for seed dor-mancy. It also causes stomata to close in times of drought in an effort to con-serve water.

B. Some plant growth regulators are man-made synthetic growth regulators. Thesesynthetic growth regulators can be applied to plants to get a myriad of changes.These changes often make the plant better or more saleable.

Begin the lesson with an interest approach. Identify the objectives of the lessonand key terms related to cellular respiration. Further prepare the students byhaving them read related sections of text materials identified in the resourceslist. Require students to take notes on the major points presented in thechapter. Follow the reading session with a discussion on plant hormones. UseVM–A—Plant Hormones And Plant Growth, to highlight interactions betweenplant hormones during various stages of plant growth. Have the students expandtheir notes based on the discussion. The discussion can also serve as a way tomonitor students’ mastery of the material. Enhance the lesson with a laboratoryactivity, LS–A: Ethylene and Ripening Fruit.

Objective 2: Define tropism and examine the types of tropisms.

Anticipated Problem: What are plant tropisms?

II. External stimuli and environmental conditions cause plants to respond in certainways. A plant response to an external stimuli is known as tropism. Three significanttropisms are phototropism, gravitropism, and thigmotropism.

A. Phototropism is a plant’s response to the source of light. Auxins move down theshaded side of the plant stem. The presence of auxins causes the cells on the


� www.MYcaert.com


shady side of the stem to elongate more than cells than the bright side of thestem. The result is a stem that bends towards the light. Under low light or darkconditions cells elongate on all sides of the stem. The result is an appearance ofthe stem stretching. Stretching due to low light is known as etiolation.

B. Gravitropism also referred to as geotropism is a plant response to gravity. Thestems of plants laid on their side curve upward. In this scenario auxins settle tothe bottom side of the stem and cause cells to elongate.

C. Thigmotropism is a response to mechanical stimuli. A good example is thetendrils of a cucumber plant. When the tendrils touch an object, the response isto curl around that object.

Engage the students in discussion on tropisms. Use transparency mastersVM–B—Phototropism and VM–C—Gravitropism, in a PowerPoint presentation oras overheads to illustrate concepts. Have the students expand their notes basedon the discussion. Ask questions during instruction to gauge studentunderstanding of the concepts. Have the students conduct laboratory exerciseLS–B: Observing Gravitropism of Germinating Seeds.

Objective 3: List examples of synthetic growth regulators and discuss how and whythey are used.

Anticipated Problem: What are synthetic growth regulators and their uses?

III. Synthetic growth regulators are used in agriculture to regulate plant growth.

A. Synthetic auxins are also used in the horticulture industry to promote rooting ofcuttings. Cuttings are treated with synthetic growth regulators to increase thenumber of cuttings that form roots, to speed rooting, to increase the number andquality of roots, and to increase the uniformity of the roots.

1. Some materials are used extensively in the horticulture industry to promote therooting of cuttings. The two synthetic root-promoting materials most widelyused are naphthaleneacetic acid (NAA) and indolebutyric acid (IBA). IBA isregarded as the best material for general use. It can be used with a wide vari-ety of plants and it is nontoxic over a wide range of concentrations. Thesematerials are available in a liquid formulation or mixed with talc.

B. Growth retardants are widely used in the greenhouse industry. These chemicalsinhibit the action of gibberellins on stem elongation. As a result, plants are morecompact. Compact plants are more attractive, often greener, and easier totransport. Although growth is slowed, flowers tend not to be affected.

C. A number of herbicides are classified as growth regulators due to their mode ofaction. Growth regulator herbicides disrupt hormone balance and proteinsynthesis. Symptoms of damage include abnormal growth. Leaves may cup,crinkle, become brittle, and form parallel veins. Stems may display a twisting orepinasty. Callus tissue may also form. The herbicides are absorbed primarily


� www.MYcaert.com


through the leaves and are translocated through both the xylem and phloem.Growth regulator herbicides are effective with broadleaf weeds. Banvel, Clarity, 2,4-D, and Stinger are growth regulator herbicides.

Lead a lecture-discussion on synthetic growth regulators. Call upon students toparticipate in the discussion. Use visual aids, such as a chalkboard or overheadprojector, to illustrate main points.

Objective 4: Describe commercial uses of plant growth regulators.

Anticipated Problem: How are plant growth regulators used commercially?

IV. Plant growth regulators are used in agricultural practices to improve the quality andquantity of yields.

A. Auxins in the forms of indoleacetic acid (IAA) and indolebutyric acid (IBA) arewidely used to speed the rooting of cuttings in the horticulture industry.Naphthaleneacetic acid (NAA) is sprayed on apples to prevent pre-harvest drop ofthe fruit.

B. Gibberellins are used to induce flowering. Some plants that respond by floweringare carrots, endive, cabbage, turnips, and chrysanthemums. Gibberellins serve asgrowth stimulants making plants, including sugar cane, grow larger. Gibberellinsare used with some plant species, such as grapes, to produce larger fruit.

C. Cytokinins have been shown to extend the shelf life of lettuce. Cytokinins are alsoan important ingredient of tissue culture medium, as they promote cell division.

D. Ethylene is used in the ripening of fruits before being placed on grocery shelves.

E. Many synthetic growth regulators are used to regulate plant growth. Somepromote growth. Others inhibit growth. Growth retardants are widely used in thehorticulture industry to keep plants compact.

Relate the discussion to uses of plant hormones and the importance of planthormones to the agriculture industry. Ask questions to assess studentunderstanding of the concepts and to determine if re-teaching is necessary.Review the material presented in this lesson, and evaluate student mastery ofthe material.

� Review/Summary. Base review and summary of the lesson content on the learningobjectives. It is beneficial to review material addressing an objective before moving on withinstruction on the next objective. Have students explain terms, processes outlined in thelesson, and the content associated with each objective. Student responses can be used indetermining which objectives require greater review or whether further instruction isnecessary. Questions at the end of each chapter in the recommended textbooks may alsobe used in the review/summary.


� www.MYcaert.com


� Application. Use the included visual masters and lab sheets to apply the informationpresented in the lesson.

� Evaluation. Focus the evaluation of student achievement on mastery of the objectivesstated in the lesson. Measure student performance on classroom participation, laboratoryassignments, and written tests or quizzes. The sample written test can also be used.

� Answers to Sample Test:

Part One: Matching

1. d

2. b

3. g

4. j

5. i

6. f

7. h

8. a

9. e

10. c

Part Two: Multiple Choice

1. c

2. d

3. a

4. c

5. b

Part Three: Short Answer

1. auxins, gibberellins, cytokinins, abscisic acid, ethylene

2. Phototropism is a plant’s response to the source of light. Auxins move down theshaded side of the plant stem. The presence of auxins causes the cells on theshady side of the stem to elongate more than cells than the bright side of the stem.The result is a stem that bends towards the light. Under low light or dark conditionscells elongate on all sides of the stem. The result is an appearance of the stemstretching. Stretching due to low light is known as etiolation. Gravitropism, alsoreferred to as geotropism, is a plant response to gravity. The stems of plants laid ontheir side curve upward. In this scenario auxins settle to the bottom side of the stemand cause cells to elongate. Thigmotropism is a response to mechanical stimuli. Agood example is the tendrils of a cucumber plant. When the tendrils touch anobject, the response is to curl around that object.


� www.MYcaert.com


3. Auxins in the forms of indoleacetic acid (IAA) and indolebutyric acid (IBA) are widelyused to speed the rooting of cuttings in the horticulture industry. Naphthaleneaceticacid (NAA) is sprayed on apples to prevent pre-harvest drop of the fruit. Gibberellinsare used to induce flowering. Some plants that respond by flowering are carrots,endive, cabbage, turnips, and chrysanthemums. Gibberellins serve as growthstimulants making plants, including sugar cane, grow larger. Gibberellins are usedwith some plant species, such as grapes, to produce larger fruit. Cytokinins havebeen shown to extend the shelf life of lettuce. Cytokinins are also an importantingredient of tissue culture medium, as they promote cell division. Ethylene is usedin the ripening of fruits before being placed on grocery shelves. Growth retardantsare widely used in the horticulture industry to keep plants compact. Growthregulator herbicides disrupt hormone balance and protein synthesis.


� www.MYcaert.com


Sample TestName ________________________________________

Plant Growth Regulators

� Part One: Matching

Instructions: Match the term with the correct definition.

a. abscisic acid f. gravitropismb. auxins g. phototropismc. cytokinins h. plant growth regulatorsd. ethylene i. thigmotropisme. gibberellins j. growth retardant

_____1. A colorless gas that speeds the aging of plant parts, particularly fruit

_____2. A group of hormones that have a primary role in promoting cell elongation

_____3. A plant’s response to the source of light

_____4. Inhibit cell elongation and keep plants compact

_____5. A response to mechanical stimuli

_____6. A plant response to gravity

_____7. Natural occurring or synthetic chemicals that regulate plant growth and development

_____8. A growth-inhibiting hormone largely responsible for seed dormancy

_____9. Plays a key role in the development of flowers and in the production of enzymes duringseed germination

____10. Hormones responsible for cell division and differentiation

� Part Two: Multiple Choice

Instructions: Write the letter of the correct answer.

_____1. What term is used to describe stretching of a plant due to low light?

a. apical dominance

b. elasticity

c. etiolation

d. phototropism


� www.MYcaert.com


_____2. What is a plant response to an external stimuli?

a. abscission

b. reaction

c. symbiosis

d. tropism

_____3. What is the meaning of apical dominance?

a. The apical meristem has dominance over the lateral buds.

b. The lateral meristem controls growth above.

c. The meristem tissue takes over surrounding tissues.

d. The vegetative growth is dominant over root growth.

_____4. What is a common synthetic root-promoting materials used in the propagation ofplants?

a. Banvel

b. indoleacetic acid (IAA)

c. indolebutyric acid (IBA)

d. plant growth regulators (PGR)

_____5. Which plant hormone encourages the growth of lateral shoots, inhibits the branching ofthe roots, and is an ingredient in tissue culture medium?

a. auxins

b. cytokinins

c. ethylene

d. gibberellins

� Part Three: Short Answer

Instructions: Complete the following.

1. List five plant hormones.

2. Define the three plant tropisms.

3. Give five examples of how plant growth regulators are used in the agricultural industry.


� www.MYcaert.com


VM–A

PLANT HORMONES ANDPLANT GROWTH

PhysiologicalActivity Auxin Gibberellin Cytokinin Ethylene

AbscisicAcid

SeedGermination

Promotes Inhibits

Growth ofSeedling intoMature Plant

Cellelongation

Cellelongation

and division

Cell divisionand

differentiation

ApicalDominance

Inhibits lateralbud

development

Promoteslateral bud

development

Flower Initiation Stimulatesflowering insome plants

FruitDevelopmentand Ripening

Development Development Promotesripening

Leaf Abscision Inhibits Inhibits Promotes

Winter Dormancy Breaksdormancy

Promotesdormancy

Seed Dormancy Breaksdormancy

Promotesdormancy


� www.MYcaert.com


VM–B

PHOTOTROPISM


� www.MYcaert.com


VM–C

GRAVITROPISM


� www.MYcaert.com


LS–AName ________________________________________

Ethylene and Ripening Fruit

Ethylene, a simple organic gas, is produced in ripe fruit. Accumulation of the gas speeds theaging of plant cells and thus the ripening process of fruits. The old saying that one rottenapple spoils the whole barrel has scientific basis. Bananas, pears, kiwi, tomatoes, and otherfruits can be forced to ripen by exposing them to ethylene gas.

Objective

Students will observe effects of ethylene on ripening fruit.

Materials

� an apple

� two green bananas from the same bunch

� two brown paper sandwich bags

� a paring knife

Procedure

1. Tightly seal a green banana in a paper bag.

2. In a second paper bag tightly seal a green banana with a slice of apple.

3. Observe the bananas daily for a week.

Anticipated Results

The cut apple produces and releases small amounts of ethylene gas. Ethylene gas plays a rolein aging of plant tissues and ripening fruit. The presence of ethylene causes fruit to ripen. Thebanana with the apple slice should ripen more quickly than the other.


� www.MYcaert.com


LS–BName ________________________________________

Observing Gravitropism of

Germinating Seeds

The first step in the germination process is the absorption of water. As the seed swells andgrowth begins, the seed coat ruptures. The root of the embryo emerges to quickly establish itsrole of absorbing water and nutrients from the soil. Roots respond to gravitropism. That is,they grow downward through the soil in response to gravity. How can the effects of gravity ongerminating seeds be observed?

Materials

� floral foam (one slice for each student)

� paring knife

� sandwich-sized sealable plastic bags

� corn seeds soaked over night (other large seeds can be used)

� 4 seeds for each student

Procedure

1. Slice the floral foam into ½" slices with the knife, much like slicing bread.

2. Push four corn seeds firmly in place in the floral foam. Orient each seed in a differentdirection; pointed side up, pointed side down, pointed side to the right, and pointed sideto the left.

3. Place the slice of floral foam into the plastic bag. Add enough water to saturate the foam.Pour off excess water and close the bag.

4. Place the bag in a bright location. Avoid putting the bag in direct sunlight as heat couldbuild up and kill the seeds.

5. Observe the seeds daily. What do you expect the seeds to do? How quickly did their rootsemerge? What direction the roots grow?


� www.MYcaert.com


plant growth regulators - wikispacesgrowth+regulators... · some plant growth regulators ......

Documents