Microbial Genetics

• Antagonistic Action of ABA on Gibberellin: In germinating cereal seeds (barley, wheat), gibberellins (GA) induce the de novo transcription of hydrolytic enzymes (such as $\alpha$-amylase) in the aleurone layer by promoting GAMYB expression.
• Suppression Mechanism: Abscisic acid (ABA) directly suppresses this GA-mediated induction by activating protein kinases (such as PKABA1) and transcriptional repressors that silence the $\alpha$-amylase promoter, thereby maintaining seed dormancy.

Correct option: (3) Abscisic acid

• Richmond-Lang Effect (1957): Cytokinins significantly delay leaf senescence and retard chlorophyll degradation by maintaining protein synthesis, suppressing protease activity, and actively mobilizing nutrients to cytokinin-treated tissues.
• Roles of Other Hormones: Auxins promote apical dominance and rooting; gibberellins promote stem elongation and seed germination; ethylene and abscisic acid promote senescence and abscission.

Correct option: (3) Cytokinins

• Multi-Parent Population Designs in Plants:
• NAM (Nested Association Mapping): Integrates the structural advantages of biparental linkage mapping and association mapping by crossing a single reference parent to multiple diverse founder lines.
• MAGIC (Multi-parent Advanced Generation Inter-Cross): Inter-crosses multiple diverse founder inbreds (typically 4, 8, or 16) through several generations of systematic recombining, producing high-resolution mapping populations.
• Biparental Designs: RIL (Recombinant Inbred Lines), NIL (Near Isogenic Lines), BC (Backcross), and TC (Testcross) are traditional biparental designs.

Correct option: (3) NAM and MAGIC

• Statement (I) is True: Diethylpyrocarbonate (DEPC) is a strong chemical modifier routinely used to treat water, buffers, and glassware to eliminate ribonuclease (RNase) contamination before RNA isolation and manipulation.
• Statement (II) is False: DEPC is a chemical alkylating agent that carboethoxylates the active-site histidine residues (specifically $N^\epsilon$ or $N^\delta$ of the imidazole ring) of ribonucleases, causing irreversible covalent denaturation, NOT a non-covalent transition state analog.
• Conclusion: Statement (I) is true but Statement (II) is false.

Correct option: (3) Statement (I) is true but Statement (II) is false.