Practice important
Seed Dormancy Maintenance
MCQ questions and answers.
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MCQ Questions
1. Which hormonal relationship most directly maintains primary seed dormancy after maturation?
A.
High abscisic acid activity relative to gibberellin activity
B.
High gibberellin activity relative to abscisic acid activity
C.
Equal abscisic acid and gibberellin activity in the embryo
D.
Suppression of abscisic acid synthesis with increased ethylene production
Correct Answer:
High abscisic acid activity relative to gibberellin activity
Explanation:
Abscisic acid maintains seed dormancy by inhibiting embryo growth and preventing premature germination, whereas gibberellins generally promote germination. A high ABA-to-GA balance therefore favors dormancy maintenance.
2. A mutant seed is unable to synthesize abscisic acid during late embryogenesis. Which defect would most directly indicate failure of dormancy maintenance?
A.
Premature germination before favorable environmental conditions
B.
Permanent inability of the embryo to absorb water
C.
Excessive formation of chlorophyll in the dry seed
D.
Complete failure of seed coat formation in every tissue
Correct Answer:
Premature germination before favorable environmental conditions
Explanation:
ABA accumulation during seed development suppresses precocious embryo growth and germination. Without sufficient ABA, seeds may undergo vivipary or germinate prematurely while still attached to the parent plant.
3. Which ABA-mediated event most directly prevents the embryo of a dormant seed from initiating growth?
A.
Activation of genes that promote reserve mobilization and cell expansion
B.
Repression of germination-associated gene expression and embryo growth
C.
Stimulation of radicle emergence through increased cell elongation
D.
Promotion of chloroplast development in the dry embryo
Correct Answer:
Repression of germination-associated gene expression and embryo growth
Explanation:
ABA maintains dormancy by suppressing transcriptional and cellular processes required for germination, including embryo growth and the transition from the dormant to the growing state.
4. A seed remains dormant despite adequate water and oxygen because its ABA concentration remains high. Which change would most likely release this dormancy?
A.
Further increase in ABA synthesis
B.
Reduction in ABA concentration or sensitivity
C.
Inhibition of all embryo metabolic activity
D.
Increase in the ABA-to-gibberellin ratio
Correct Answer:
Reduction in ABA concentration or sensitivity
Explanation:
Dormancy is maintained when ABA levels or ABA responsiveness remain high. Dormancy release commonly requires ABA catabolism, reduced ABA signaling, or a decline in ABA dominance relative to germination-promoting signals.
5. Which observation best distinguishes ABA-maintained physiological dormancy from simple lack of water?
A.
The seed fails to germinate even after water uptake under otherwise favorable conditions
B.
The seed becomes heavier immediately after being placed in water
C.
The seed coat becomes hydrated during imbibition
D.
The embryo increases its water content during soaking
Correct Answer:
The seed fails to germinate even after water uptake under otherwise favorable conditions
Explanation:
Physiological dormancy involves internal biochemical inhibition, particularly ABA-mediated suppression of embryo growth. Thus, a dormant seed can imbibe water but still fail to germinate when external conditions are favorable.
6. During seed maturation, why is accumulation of ABA advantageous for maintaining dormancy?
A.
It prevents premature germination and promotes the acquisition of desiccation tolerance
B.
It forces immediate radicle emergence before seed dispersal
C.
It increases gibberellin synthesis to accelerate embryo elongation
D.
It prevents the embryo from entering a metabolically quiescent state
Correct Answer:
It prevents premature germination and promotes the acquisition of desiccation tolerance
Explanation:
ABA acts during maturation to inhibit precocious germination and support the seed's preparation for drying. These functions help the mature seed remain dormant and survive subsequent desiccation.
7. A researcher applies gibberellin to a dormant seed, but germination remains suppressed because ABA signaling is constitutively active. What does this result demonstrate?
A.
ABA-mediated inhibition can override a germination-promoting gibberellin signal
B.
Gibberellin always maintains dormancy more strongly than ABA
C.
ABA has no role after seed maturation is complete
D.
Germination depends only on water uptake and not hormonal balance
Correct Answer:
ABA-mediated inhibition can override a germination-promoting gibberellin signal
Explanation:
Seed dormancy reflects the balance between inhibitory ABA signaling and promotive gibberellin signaling. Constitutive ABA signaling can maintain repression of embryo growth even when gibberellin is supplied.
8. Which molecular change would most likely cause a seed to lose dormancy while retaining the ability to synthesize normal amounts of ABA?
A.
A mutation that reduces cellular sensitivity to ABA
B.
A mutation that increases ABA receptor activity
C.
A mutation that enhances ABA-responsive gene expression
D.
A mutation that decreases gibberellin signaling in the embryo
Correct Answer:
A mutation that reduces cellular sensitivity to ABA
Explanation:
ABA must be perceived and transduced to maintain dormancy. If embryo cells become insensitive to ABA, normal hormone levels may no longer suppress germination, causing reduced dormancy.
9. Which experimental result would provide the strongest evidence that ABA maintains dormancy through inhibition of embryo growth rather than through prevention of water uptake?
A.
Dormant seeds imbibe water, but isolated embryos resume growth after ABA removal
B.
Dormant seeds remain completely dry when placed in water
C.
ABA-treated seeds lose all water from their seed coats
D.
Seeds with high ABA content show greater water absorption than untreated seeds
Correct Answer:
Dormant seeds imbibe water, but isolated embryos resume growth after ABA removal
Explanation:
If seeds can take up water but their embryos remain inhibited until ABA is removed, the evidence supports ABA-dependent suppression of embryo growth as a mechanism of dormancy maintenance.
10. A seed population shows increased ABA catabolism during storage and subsequently germinates more readily under favorable conditions. What is the most direct interpretation?
A.
Loss of ABA reduces the hormonal inhibition responsible for dormancy maintenance
B.
ABA catabolism strengthens dormancy by increasing ABA accumulation
C.
ABA catabolism prevents the embryo from responding to gibberellin
D.
Loss of ABA permanently blocks water uptake by the seed
Correct Answer:
Loss of ABA reduces the hormonal inhibition responsible for dormancy maintenance
Explanation:
Catabolism lowers the ABA level in the seed. Reduced ABA-mediated inhibition allows germination-promoting processes to become more effective, thereby weakening dormancy and increasing germination potential.
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