Q.36 Determine the correctness or otherwise of the following Assertion (a) and Reason (r).
Assertion: In direct somatic embryogenesis, embryos are developed without going through callus
formation.
Reason: This is possible due to the presence of pre-embryonically determined cells.
(A) Both (a) and (r) are true but (r) is not the correct reason for (a)
(B) (a) is false but (r) is true
(C) (a) is true but (r) is false
(D) Both (a) and (r) are true and (r) is the correct reason for (a)
Direct somatic embryogenesis enables rapid plant regeneration from explants without callus phase, ideal for clonal propagation in biotechnology. The assertion claims embryos form directly, bypassing callus, while the reason attributes this to pre-embryonically determined cells (PEDCs). Both statements align perfectly, making the reason the direct cause.
Assertion and Reason Defined
Assertion (a): In direct somatic embryogenesis, embryos develop without callus formation.
True. Unlike indirect embryogenesis requiring dedifferentiated callus, direct SE produces embryos straight from explant cells like epidermis or sub-epidermal layers, maintaining tissue polarity.
Reason (r): Possible due to pre-embryonically determined cells (PEDCs).
True. PEDCs exist as competent cells pre-patterned for embryogenic fate in explants, bypassing dedifferentiation; upon hormonal cues (auxin/cytokinin), they directly form proembryonic masses without disorganized callus.
Correct Answer
Option (D) Both (a) and (r) are true and (r) is the correct reason for (a).
PEDCs directly respond to signals, forming somatic embryos without callus proliferation, distinguishing direct from indirect pathways.
| Statement | Truth Value | Key Feature |
|---|---|---|
| Assertion (a) | True | No callus; embryos from explant surface cells |
| Reason (r) | True | PEDCs pre-determined, trigger embryogenesis directly |
| Relation | (r) causes (a) | PEDCs eliminate callus requirement |
Option Explanations
(A) Both true but (r) not correct reason: Incorrect. PEDCs specifically enable callus bypass by their pre-committed embryogenic potential.
(B) (a) false but (r) true: Incorrect. Assertion defines direct SE standardly—embryos form directly from explants sans callus.
(C) (a) true but (r) false: Incorrect. PEDCs represent established mechanism; contrasted with induced embryogenic determined cells (IEDCs) in indirect SE via callus.
(D) Both true and (r) correct reason: Correct. Pre-determined cells in meristematic tissues (apices, immature embryos) directly embryogenize under optimized media (high auxin like 2,4-D).
Practical Implications
Direct SE excels in species like coffee, conifers, and orchids for synthetic seed production and genetic transformation. Protocols avoid cytokinin excess to favor PEDC activation. In your biotechnology context, combining with elicitors boosts secondary metabolites from embryogenic cultures while maintaining genetic fidelity over callus-based methods.
