Ch 39 Plant Behavior Flashcards
Plant horomones
Chemical signals that modify or control one or more specific physiological processes within a plant
Plant hormones control what?
A plant’s dynamic response to its environment
Are plant hormones produced in high or low concentrations?
Very low concentrations
What can greatly affect growth and development of a plant organ?
Very small amounts of plant hormones
In general, how do hormones control plant growth and development?
By affecting the division, elongation, and differentiation of cells
Tropism
Any response resulting in curvature of organs toward or away from a stimulus
Phototropism
The growth towards light
What was the first plant tropism and its hormonal basis to be investigated?
Phototropism
What was the first plant hormone discovered in association with phototropism?
Auxin
Auxin
Refers to any chemical that promotes elongation of coleoptiles
Coleoptiles
Grass shoots
Where is auxin produced?
In shoot tips
Where is auxin transported?
Down the stem
According to the acid growth hypothesis, auxin stimulates what?
Proton pumps that lower pH and activate expansins and enzymes that loosen the cell wall
Major responses to auxin
Stimlulates cell elongation
Regulates branching and organ bending
Major responses to cytokinins
Stimulate plant cells division
Promotes later bud growth and slow organ death
Major response to gibberellins
Promote stem elongation
Helps seeds break dormancy and use stored reserves
Major responses to brassinosteroids
Induce cell elongation and division
Brassinosteroids are chemically similar to what?
Sex hormones of animals
Major responses to abscisic acid
Protomotes stomatal closure in response to drought
Promotes seed dormancy
Major responses to strigolactones
Regulate apical dominance, seed germination, and mycorrhizal associations
Major responses to ethylene
Mediates fruit ripening
Cytokinins are produced by in what?
Actively growing tissues (roots, embryos, and fruits)
What three plant hormones interact in the control of apical dominance
1) Cytokinins
2) Auxins
3) Strigolactone
Apical dominance
A terminal bud’s ability to suppress development of axillary buds
What happens if a terminal bud is removed?
Plants become bushier
What two plants hormones interact to loosen cell walls and facilitate entrance into the cells by expansins?
1) Auxin
2) Gibberelins
Gibberelins control what?
Bolting
Bolting
The rapid growth of a plant’s flowering stalk
What two plant hormones that are necessary for flowers to yield fully-developed fruits?
1) Auxins
2) Gibberelins
Gibberelins initiate secretions of what?
Digestive enzymes that make nutrients available to the plant embryo
In some seeds, germination is stimulated by what?
When the hormone abscisic acid (ABA) is removed by heavy rain, light, or prolonged cold
What can cause precocious (early) germination of seeds?
Inactive or low levels of ABA
How is the plant hormone ethylene distributed?
As a gas
When is ethylene produced?
1) During fruit ripening
2) In response to stress (drought, flooding, injury, infection)
Ethylene induces what kind of response?
A triple response
Triple response
Allows a growing shoot to avoid obstacles
Three steps of triple response
1) Slowing of stem elongation
2) Thickening
3) Horizontal growth
What usually initiates hormonal responses leading to flowering and fruiting?
A photoperiod
Photoperiod
The relative lengths of night and day
Short-day plants
Plants that flower when a light period is shorter than a critical legnth
Long-day plants
Plants that flower when a light period is longer than a critical length
Thigmotropism
Growth in response to touch that occurs in vines and other climbing paltns
Thigmomorphogenesis
Refers to changes in form that result from mechanical disturbances
Touching young plants can result in what?
Slowed apical growth
Gravitropism
Response to gravity
Roots show what kind of gravitropism?
Positive gravitropism
Shoots show what kind of gravitropism?
Negative gravitropism
Statoliths
Dense cytoplasmic components
How doe plants detect gravity?
By the settling of statoliths
Secondary compounds
Compounds produced for defense
Toxins
Secondary compounds produced in small amounts
Inhibitors of digestion
Secondary compounds produced in large amounts
Alkaloids
A major group of bitter-tasting plant toxin
What are alkaloids derived from?
Amino acids
Four known alkaloids
1) Caffeine
2) Nicotine
3) Morphine
4) Strychnine
Phenolics
Have antiseptic properties or inhibit digestion
How do phenolics inhibit digestion?
By binding proteins and interfering with enzymes
Three known phenolics
1) Tannins
2) Lignin
3) Cannibinoids
Plants damaged by insects release chemicals to:
1) Warn other plants of the same species
2) “Recruit” predators that help defend against predators
