Biology · Plant Growth and Development · NEET
NCERT lists inhibitory substances that keep seeds dormant: abscisic acid (ABA), phenolic acids, and para-ascorbic acid. These chemicals block germination until they are washed out or broken down. ABA is the main hormone here: it induces dormancy and helps seeds survive drying (desiccation) and bad conditions.
ABA INDUCES and MAINTAINS dormancy. It does NOT break it. Think: ABA is a brake. The hormone that BREAKS dormancy and starts germination is gibberellin (GA). So if a question says a hormone 'breaks seed dormancy', the answer is GA (or ethylene, which also breaks seed and bud dormancy), never ABA.
No. This is a very common trap. Gibberellic acid (GA3) is a GROWTH PROMOTER; it breaks dormancy and starts germination. So in a question asking which is 'NOT an inhibitory substance governing seed dormancy', the answer is gibberellic acid. The real inhibitory substances are ABA, phenolic acid and para-ascorbic acid.
They are antagonists (opposite actions). NCERT states: 'ABA acts as an antagonist to GAs.' ABA keeps the seed dormant; GA overcomes ABA and triggers germination. The ratio of ABA to GA decides whether the seed stays asleep or wakes up. This ABA vs GA balance is a favourite NEET idea.
ABA is a general plant growth inhibitor and inhibitor of metabolism. It closes stomata during water shortage, inhibits seed germination, and raises tolerance to stresses like drought. Because it helps the plant cope with unfavourable (stress) conditions, NCERT calls ABA the 'stress hormone'.
Dormancy is useful. By staying dormant, seeds withstand desiccation and wait for the right season, so the plant does not germinate at a bad time. ABA-induced dormancy and the hard seed coat protect the embryo. Dormancy and dehydration of mature seeds are also crucial for storing seeds as food and for raising the next crop.
Which of the following is not an inhibitory substance governing seed dormancy?
Read the following statements on plant growth and development. A. Parthenocarpy can be induced by auxins. B. Plant growth regulators can be involved in promotion as well as inhibition of growth. C. Dedifferentiation is a pre-requisite for re-differentiation. D. Abscisic acid is a plant growth promoter. E. Apical dominance promotes the growth of lateral buds. Choose the option with all correct statements.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a resting state in which a living (viable) seed does not germinate even when temperature, water and oxygen are favourable, mainly due to inhibitory substances like ABA.
Abscisic acid (ABA), phenolic acids, and para-ascorbic acid. Gibberellic acid is NOT one of them; it breaks dormancy.
Gibberellin (GA) breaks dormancy and promotes germination. Ethylene also breaks seed and bud dormancy and initiates germination. ABA does the opposite.
ABA closes stomata to save water, inhibits germination and metabolism, and increases tolerance to stresses such as drought, helping the plant survive unfavourable conditions.
They are antagonists. ABA induces and maintains dormancy; GA breaks it. Their balance (ABA:GA ratio) decides whether the seed germinates.
