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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.
A. Describe the role of the apical meristem in plant growth.
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
A. Describe the role of the apical meristem in plant growth.
A. Describe the role of the apical meristem in plant growth.
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
A. Describe the role of the apical meristem in plant growth.
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
A. Describe the role of the apical meristem in plant growth.
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.
B. Identify plant hormones and explain their functions.
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
B. Identify plant hormones and explain their functions.
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!
B. Identify plant hormones and explain their functions.
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
B. Identify plant hormones and explain their functions.
Two types of hormones
• Promoters vs. Inhibitors– Promoters- cause faster growth– Inhibitors- reduce growth• Also called a growth retardant
B. Identify plant hormones and explain their functions.
Hormones
• Auxins• Gibberellins• Cytokinins• Ethylene• Abscisic acid
B. Identify plant hormones and explain their functions.
Hormones in a nutshell
Hormone Effects
Auxins Cell enlargement and differentiation
Giberellins Cell enlargement and differentiation
Cytokinins Cell division
Abscisic Acid Dormancy
Ethylene Ageing
B. Identify plant hormones and explain their functions.
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
B. Identify plant hormones and explain their functions.
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
B. Identify plant hormones and explain their functions.
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
B. Identify plant hormones and explain their functions.
Abscisic Acid
• Growth inhibiting hormone• Plays a key role in seed dormancy• Causes stomates to close in drought
conditions to conserve water• Growth retardant
B. Identify plant hormones and explain their functions.
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
C. Explain plant tropisms.
The ‘tropisms’
• Phototropism• Gravitropism or Geotropism• Chemotropism• Thigmitropism• Hydrotropism
C. Explain plant tropisms.
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
C. Explain plant tropisms.
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
Tropism Stimulus Response
Phototropism
Gravitropism
Chemitropism
Thigmitropism
Hydrotropism
C. Explain plant tropisms.
C. Explain plant tropisms.
C. Explain plant tropisms.
Important minerals in soil
C. Explain plant tropisms.
C. Explain plant tropisms.
C. Explain plant tropisms.
Step 3 – Review your observations
Tropism Stimulus Response
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
C. Explain plant tropisms.
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
C. Explain plant tropisms.
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!
D. Differentiate between synthetic growth regulators and plant hormones.
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)
D. Differentiate between synthetic growth regulators and plant hormones.
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
D. Differentiate between synthetic growth regulators and plant hormones.
PGR’s
• Growth retardants can be used on hedges and lawns to slow growth and decrease maintenance.
TREATED UNTREATED
D. Differentiate between synthetic growth regulators and plant hormones.
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
E. Describe the benefits of using plant growth regulators.
Auxins
• Speed up the rooting of plant cuttings– Indoleacetic acid (IAA)– Indolebutyric acid (IBA)
• Prevent pre-harvest fruit drop on apples– Naphthaleneacetic acid (NAA)
E. Describe the benefits of using plant growth regulators.
Gibberellins
• Induces flowering• Growth stimulant to make larger stalks and
fruit
E. Describe the benefits of using plant growth regulators.
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.
E. Describe the benefits of using plant growth regulators.
Cytokinins
• Cytokinins promote cell division and enlargement to promote senescence
• Leaves grow themselves to death
E. Describe the benefits of using plant growth regulators.
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)
E. Describe the benefits of using plant growth regulators.
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.
E. Describe the benefits of using plant growth regulators.
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