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Questions and Answers
Which function is specifically associated with abscisic acid in plants?
Which function is specifically associated with abscisic acid in plants?
What role do plant hormones play in multicellular organisms?
What role do plant hormones play in multicellular organisms?
Which of the following processes is NOT influenced by plant hormones?
Which of the following processes is NOT influenced by plant hormones?
What characteristic distinguishes plant hormones from other signaling molecules?
What characteristic distinguishes plant hormones from other signaling molecules?
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Which plant hormone is primarily linked to senescence and fruit ripening?
Which plant hormone is primarily linked to senescence and fruit ripening?
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What role does ethylene play in leaf abscission?
What role does ethylene play in leaf abscission?
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How does the balance of ethylene and auxin affect leaf abscission?
How does the balance of ethylene and auxin affect leaf abscission?
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Which statement best describes programmed cell death in the context of ethylene?
Which statement best describes programmed cell death in the context of ethylene?
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What is true about evergreen species in relation to leaf abscission?
What is true about evergreen species in relation to leaf abscission?
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Which is a consequence of ethylene's effect on cells during leaf abscission?
Which is a consequence of ethylene's effect on cells during leaf abscission?
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Which of the following describes the role of secondary messengers in hormone signaling?
Which of the following describes the role of secondary messengers in hormone signaling?
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What is the primary function of auxin in plant growth?
What is the primary function of auxin in plant growth?
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Which hormone is NOT classified as a growth promoter?
Which hormone is NOT classified as a growth promoter?
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What role does the apex play in the regulation of plant growth?
What role does the apex play in the regulation of plant growth?
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How does environmental factors affect hormone metabolism?
How does environmental factors affect hormone metabolism?
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Which of the following hormones is primarily associated with inducing dormancy?
Which of the following hormones is primarily associated with inducing dormancy?
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What is a significant difficulty in identifying hormone receptors?
What is a significant difficulty in identifying hormone receptors?
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Which of the following is an example of an auxin-like herbicide?
Which of the following is an example of an auxin-like herbicide?
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What is the primary function of auxin in plants?
What is the primary function of auxin in plants?
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Which hormone is most commonly associated with promoting cell division in plants?
Which hormone is most commonly associated with promoting cell division in plants?
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What role does abscisic acid play during seed dormancy?
What role does abscisic acid play during seed dormancy?
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How does gibberellic acid affect seed development?
How does gibberellic acid affect seed development?
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What triggers the ripening of fruits?
What triggers the ripening of fruits?
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Which of the following features is associated with the ripening of fruit?
Which of the following features is associated with the ripening of fruit?
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What can be a result of high levels of gibberellic acid during the first stage of embryo development?
What can be a result of high levels of gibberellic acid during the first stage of embryo development?
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What is the main consequence of an extensive shoot system concerning auxin and cytokinin?
What is the main consequence of an extensive shoot system concerning auxin and cytokinin?
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How does ethylene function in relation to fruit?
How does ethylene function in relation to fruit?
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What effect occurs when you mix fruits and flowers together?
What effect occurs when you mix fruits and flowers together?
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What determines whether a seed grows or goes dormant?
What determines whether a seed grows or goes dormant?
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What is the main role of auxin in the context of fruit and seed growth?
What is the main role of auxin in the context of fruit and seed growth?
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Which of the following hormones blocks axillary bud growth?
Which of the following hormones blocks axillary bud growth?
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How do synthetic auxins or gibberellins affect seedless fruits?
How do synthetic auxins or gibberellins affect seedless fruits?
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Study Notes
Plant Hormones BL1004
- Plant hormones control plant growth and development
- They control processes like sink-source relations, seed dormancy, seed germination, flowering, development of seed/fruit, formation of tubers/bulbs, senescence, and many more
- Hormones increase plant size or weight (growth) and direct progression through the plant's life cycle (development)
- They coordinate growth and development of cells, tissues, and organs
- Plant hormones are essential for all multicellular organisms
- Sessile organisms, like plants, must adjust to environmental changes, with hormones playing a key role in this adjustment
Plant Hormone Characteristics
- Produced by multicellular organisms
- Internal chemical signals
- Present in minute amounts
- Travel throughout the organism
- Coordinate metabolic activities
- Coordinate environmental responses
- Not produced in glands
Hormone Activity at Cell Level
- Receptor: Hormone or environmental stimulus binds to a receptor
- Signaling Cascade: Relay molecules transmit the signal
- Cellular Response: Activation of cellular responses, altering gene transcription, or enzyme activity
Hormone Reception
- "Hormone" comes from a Greek word meaning "to excite"
- Specific receptors exist for each type of hormone
- Located in the cell membrane
- Present in very low concentrations
Identifying a Hormone Receptor
- Biochemical purification is difficult
- Genetic approaches are successful, using plants with altered phenotypes
Signal Transduction
- Secondary messengers connect the receptor with the response system
- Secondary messengers transduce and amplify hormone signals
- Examples include calcium fluxes, cyclic GMP, and phosphorylation events
Cell Response
- Altered transcription of specific genes (transcriptional regulation)
- Altered activity of enzymes (post-translational regulation)
- Changes can be up or down regulated
Hormone Metabolism
- Environmental factors can alter hormone biosynthesis, transport, conjugation to sugars, perception, and degradation
Five Main Classes of Hormones
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Growth Promoters:
- Auxin and gibberellin stimulate cell expansion
- Cytokinin stimulates cell division
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Growth Inhibitors:
- Abscisic acid slows growth, promoting dormancy
- Ethylene controls ripening and cell death
Life Cycle - Apical Dominance
- The apex blocks the growth of axillary buds
- Important for light competition
- Auxin is produced in the apex and young leaves
- Blocks growth of axillary buds lower the stem
- Responsible for apical dominance
Auxin
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Generic name for chemicals with auxin-like activity
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Indole acetic acid (IAA) is the main natural auxin
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2,4-D (2,4-Dichlorophenoxyacetic acid) is an auxin-like weed killer
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Agent orange (a component of it) was used as a defoliant in the Vietnam War
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Mostly produced in shoot apex, young leaves and embryos
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Travels down to the roots
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Blocks axillary buds
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Promotes lateral root formation
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Used commercially as rooting powder
Cytokinin
- Mostly produced in root tip, as well as in embryos
- Most common type is "zeatin"
- Travels up from roots to shoots
- Promotes cell division
- Enhances sprouting of axillary buds (branching)
- Anti-ageing
Auxin & Cytokinin
- An extensive shoot produces a lot of auxin, encouraging root growth
- Extensive root systems produce a lot of cytokinin, encouraging shoot growth
- Together, auxin and cytokinin balance root and shoot growth
Life Cycle - Auxin & Fruits
- Fruits are costly investments for the plant
- Auxin and/or gibberellin, produced in the embryo, stimulate fruit growth
- No embryo = no auxin/GA= no fruit
- Flowers/young fruits are shed if there's no viable, hormone-producing embryo
Life Cycle - Fruits (Auxin and Gibberellin)
- Seedless fruits are treated with synthetic auxin or gibberellin, or a genetic mutant is used
- Synthetic auxins/gibberellins make seedless fruits possible
Seed Dormancy (Gibberellin vs Abscisic Acid)
- Seed development
- High levels of gibberellic acid promote embryo growth
- High levels of abscisic acid facilitate embryo dormancy
- Dormancy facilitates seed dispersal and survival; some dormant seeds can survive for hundreds of years
- Different stages of seed development are affected by different hormone levels
- Initial stage – high levels of gibberellic acid activate growth, while low levels of abscisic acid don't affect growth
- Second stage – Low levels of GA fail to activate growth, while high levels of ABA slow down metabolism
- Third stage – Low levels of ABA with high levels of GA facilitate metabolism
- The balance between the two hormones determines whether a seed grows or remains dormant
Life Cycle - Fruit Ripening (Ethylene)
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Timing of ripening is carefully regulated
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Plants switch from repelling to attracting consumers
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Softening occurs as starch and acids convert to sugars
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Scent and color changes occur
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Ethylene controls the process
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Ethylene burst; Positive feedback cycle; Ethylene is a gas, ripe fruit stimulates ripening in other fruits
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Worldwide trait in fruits possible by removing ethylene gas
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Ripe fruit stimulates fruit ripening and flower aging
Fruit/Flower Shelf Life
- Mixing fruits and flowers results in shorter shelf life, reduced quality, and lower nutritional content for both
- The best practice is to keep items separate
One Bad Apple Spoils The Bunch
- Ethylene is responsible for this process
Life Cycle - Ethylene
- Causes local cell death (apoptosis)
- Example of this is xylem vessels dying while surrounding cells stay alive
Life Cycle - Ethylene and Auxin
- Programmed (regulated) cell death (apoptosis)
- Leaf abscission involves local increases in ethylene and local decreases in auxin
- Local cell death at the abscission layer results in leaf shedding
Ethylene, Auxin & Leaf Abscission
- Leaf abscission involves local increases in ethylene and local decreases in auxin
- Seasonal variations in hormone levels differ among species; not all species shed their leaves in winter
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Description
This quiz explores the fascinating world of plant hormones and their crucial role in controlling growth and development in plants. You'll learn about processes influenced by hormones, their characteristics, and how they facilitate responses to environmental changes. Test your knowledge on how these essential signals impact plant biology.
