Crop Productivity & Modelling

• Features of Natural Ti-Plasmid (Agrobacterium tumefaciens):
• T-DNA Region: Contains one or more transferred DNA regions transferred and stably integrated into the host plant nuclear genome.
• Virulence (vir) Region: Encodes Vir proteins (VirA, VirG, VirD1/D2, VirE2) required for processing, excising, and delivering T-DNA into the plant cell.
• Conjugative Transfer Region: Harbors tra/trb genes enabling plasmid transfer between agrobacterial cells via bacterial conjugation.
• Absence of Antibiotic Resistance (B): Wild-type Ti-plasmids do not harbor natural antibiotic resistance genes (they encode opine synthesis/catabolism and auxin/cytokinin biosynthesis). Antibiotic markers are added in engineered binary cloning vectors.
• Conclusion: (A), (C), and (D) only are correct.

Correct option: (2) (A), (C) and (D) only.

• Definition of Denitrification: An anaerobic microbial respiratory process wherein soil bacteria reduce oxidized nitrogen forms into gaseous nitrogen species:

$$\text{NO}_3^- \rightarrow \text{NO}_2^- \rightarrow \text{NO} \rightarrow \text{N}_2\text{O} \rightarrow \text{N}_2$$

• Microbial Agents: Carried out by facultative anaerobes (Pseudomonas stutzeri, Paracoccus denitrificans) in poorly aerated or waterlogged soils, resulting in the return of fixed nitrogen to the atmosphere.

Correct option: (1) Bacterial conversion of nitrate to nitrous oxide and molecular nitrogen

• Assertion (A) is True: Biological nitrogen fixation (BNF) is executed by the two-component nitrogenase multienzyme complex comprising dinitrogenase reductase (Fe protein) and dinitrogenase (MoFe protein).
• Reason (R) is True & Explains (A): The Fe protein (reductase) couples ATP hydrolysis to deliver low-potential electrons to the MoFe protein (nitrogenase), which utilizes the catalytic FeMo cofactor (FeMoco) to bind and reduce molecular $\text{N}_2$ to $2\text{NH}_3$.
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)

• Xanthophyll Cycle Sequence: Non-photochemical quenching (NPQ) dissipates surplus excitation energy as heat via the sequential enzymatic deepoxidation of violaxanthin:

$$\text{Violaxanthin} \xrightarrow{\text{Violaxanthin de-epoxidase}} \text{Antheraxanthin} \xrightarrow{\text{Violaxanthin de-epoxidase}} \text{Zeaxanthin}$$

• Reversibility: In low light, zeaxanthin epoxidase converts zeaxanthin back to violaxanthin.
• Correct Direction: Violaxanthin $\rightarrow$ Antheraxanthin $\rightarrow$ Zeaxanthin.

Correct option: (4) Violaxanthin Antheraxanthin — Zeaxanthin