Plant and Soil Science I Standard 5: Students will describe plant anatomy and physiology concepts Objective 7: Explain the management of plant growth and.

Plant and Soil Science I

Standard 5: Students will describe plant anatomy and physiology concepts

Objective 7: Explain the management of plant growth and development

Objectives

A. Describe the role of the apical meristem in plant growth.

B. Identify plant hormones and explain their functions.

C. Explain plant tropisms.D. Differentiate between synthetic growth

regulators and plant hormones.E. Describe the benefits of using plant growth

regulators.


Meristems; a plants fountain of youth!

• Meristem: the site of actively dividing cells resulting in plant growth

• Apical (or terminal) bud: located at the end of a stem or root and gives the plant height or length

• Axillary (or lateral) bud: located on side of a stem and give the plant girth

• Apical dominance: the apical tip grows taller and longer inhibiting the growth of lateral buds



Meristems

• The meristimatic region on plants are found at tip of the outer cells on roots or shoots

• Changing the apical dominance is as simple as removing the top cells from a plant shoot


Ouch, that hurt aka ‘pinching plants’

• Pinching plants is a form of pruning that encourages branching

• Pinching plants alters the apical dominance• Pinching the plant forces the plant to focus on

growing lost stems, rather than growing height


How to pinch plants

1. Find a node on the plant you want to pinch.

2. Using a knife, scissors, or your fingers remove (pinch) the lateral shoot above the node.


What are hormones?

What is a hormone?What do hormones do?

Can you think of any examples?

Chemical Messenger

Causes a change in how the body works

Travel in the blood, secreted

by glands

Control Growth, blood sugar, sex development, mood,

metabolism.

Insulin

Testosterone

OestrogenGlucagon

ADH

HGH


Hormones in plants

What do hormones control in plants?• Roots and shoots • Seed germination• Leaf fall• Disease resistance• Fruit formation and ripening • Flowering time • Bud formation• Anything related to plant growth!


Hormones

• Naturally produced in the plant• Some are commercially important and can be

used to to produce plants as ornaments or food

• Some have different effects on different tissues


Two types of hormones

• Promoters vs. Inhibitors– Promoters- cause faster growth– Inhibitors- reduce growth• Also called a growth retardant


Hormones

• Auxins• Gibberellins• Cytokinins• Ethylene• Abscisic acid


Hormones in a nutshell

Hormone Effects

Auxins Cell enlargement and differentiation

Giberellins Cell enlargement and differentiation

Cytokinins Cell division

Abscisic Acid Dormancy

Ethylene Ageing


Auxins

• Promote cell elongation• One of the first hormones discovered in

science by Charles Darwin• The primary auxin is indoleastic acid (IAA)• There is a greater concentration of auxins in

the apical meristems, hence apical dominance• Passed from cell to cell through their cell walls• Promoter


Giberellins

• Induce cell elongation and cell division• Produced in the stem and root apical

meristems, seed embryos and young leaves• Important for plant growth and development

through flowering and/or seed germination• Promoter


Cytokinins

• Responsible for cell division and differentiation

• Produced in the roots and transported through xylem

• Aid in growth of lateral shoots• Inhibit branching of roots • Promoter


Abscisic Acid

• Growth inhibiting hormone• Plays a key role in seed dormancy• Causes stomates to close in drought

conditions to conserve water• Growth retardant


Ethylene

• Colorless gas that is emitted by aging plants• It is produced in plant stems, ripening fruit

and dying leaves• Converts starch into sugar• Growth retardant

C. Explain plant tropisms.

Sensitivity – Responding to the environment

Plants respond to stimuli in order to:• Avoid stress• Avoid being eaten• Enhance survival• Improve chances of having offspring• The way a plant grows is controlled by hormones• Plants response to external stimuli is known as a

tropism


The ‘tropisms’

• Phototropism• Gravitropism or Geotropism• Chemotropism• Thigmitropism• Hydrotropism


Stimulus vs. response

• Stimulus: something that influences an activity • Response: any behavior that results from the

stimulus• Examples:

Stimulus ResponseLack of food Hungry

No water Thirsty

Lollipops, ponies, and Ferris wheels

Happy


Step 1 – Make a copy of this table in your notes

Tropism Stimulus Response

Phototropism

Gravitropism

Chemitropism

Thigmitropism

Hydrotropism

C. Explain plant tropisms. Step 2 – Observe the following pictures to complete the table


Phototropism

Gravitropism

Chemitropism

Thigmitropism

Hydrotropism




Important minerals in soil




Step 3 – Review your observations


Phototropism Light source Stems bend or stretch (etiolation) towards light

Gravitropism Gravity Stems curve upward on a plant that is laid on its side

Chemitropism Nutrients in the soil Roots grow to nutrients in soil

Thigmitropism Mechanical stimuli Tendrils on a cucumber plant touching an object and curling around it for support

Hydrotropism Water source Roots grow to water


What controls tropisms?

• The hormone auxin controls most tropisms• Auxin promotes cell growth• Phototropism– Sunlight breaks down auxin– Plant stems indirect sunlight will have the least

amount of auxin– Area of the plant that is more shaded will have more

auxin– More cell growth on shaded side– Plant bends towards light

• Light directly over the plant • Auxins are in equal quantity• Cell elongation is equal on all

sides of the cell

• Greater light on the right side of the plant

• Auxin quantity becomes greater on the left cell

• Auxins trigger cell elongation on the left side

• Plant ‘stretches’ to the light


What controls tropisms?

• The hormone auxin controls most tropisms• Auxin promotes cell growth• Gravitropism– The plant stem that was once upright is on its side– The auxin are settle on the bottom side of the

stem– More auxin accumulate on the stems bottom side– More cell growth occurs on bottom side– Plant bends upward

D. Differentiate between synthetic growth regulators and plant hormones.

What’s the difference?

• Plant growth regulators (PGR’s) modify the plants physiological processes

• Hormones modify the plants physiological processes

• One is created by the plant the other is created in a factory!


Natural vs. Synthetic

• Natural vs. Synthetic– Natural- found naturally in plants– Synthetic- human made

• Both groups regulate or influence:– Cell division– Cell differentiation– Root and shoot growth– Senescence (plant aging)


Types of PGR’s

• Promoters vs. Inhibitors– Promoters- cause faster growth– Inhibitors- reduce growth• Used on florist crops such as poinsettia &

chrysanthemum.– They slow elongation of stems, making sturdier, fuller plants

• PGR’s have been created to model plant hormones


PGR’s

• Growth retardants can be used on hedges and lawns to slow growth and decrease maintenance.

TREATED UNTREATED


Synthetic and natural growth retardants

• Synthetic and natural growth retardants are sold under the trade names A-Rest®, B-Nine®, Bonzi®, Sumagic®, Cycocel®, and others

• The different names are used on different horticulture plants

E. Describe the benefits of using plant growth regulators.

Improve the quality and quantity

• Plant growth regulators improve the quality and quantity of agriculture commodity yields

• Most of the plant growth regulators are naturally produced by the plant


Auxins

• Speed up the rooting of plant cuttings– Indoleacetic acid (IAA)– Indolebutyric acid (IBA)

• Prevent pre-harvest fruit drop on apples– Naphthaleneacetic acid (NAA)


Gibberellins

• Induces flowering• Growth stimulant to make larger stalks and

fruit


Ethylene

• Promotes fruit ripening• Used for ripening fruit before it is placed on

grocery shelves• Pineapples will bloom when treated with

ethylene.– In commercial greenhouses, the product used for

ethylene generation is Florel® or ethephon.


Cytokinins

• Cytokinins promote cell division and enlargement to promote senescence

• Leaves grow themselves to death


Plant growth regulators

• Prevents lodging in cereal crops• Prevents pre-harvest fruit drop• Synchronizes maturity to allow mechanical

harvesting • Harvesting maturity to decrease turnover time• Historically common PGR’s– 2-4D– 2-4-5T (agent orange)


Pinching agents

• Pinching agent chemicals are used commercially to kill terminal vegetative buds.– They promote branching & a more bushy,

attractive plant.• OffShoot-0® & Atrimmec® are mainly used for this

purpose.


Vitamins

• Vitamins are sold occasionally as stimulants for plant growth and for use after transplanting

• Vitamin effectiveness has not been determined fully– Limited experiments

• Overall, it is very possible that vitamins do improve plant growth in some cases

– They should never be used in place of fertilizers orproven-effective chemicals sold for use on plants

Plant and Soil Science I Standard 5: Students will describe plant anatomy and physiology concepts Objective 7: Explain the management of plant growth and.

Documents

plant hormones

plant growth apical

plant growth regulators

plant height

management of plant

plant anatomy

plant tropisms

plant shoot slide