ICAR AIEEA PG 2024 - Plant Biotechnology

Verification of photosynthetic adaptations:
Statement A (Correct): Sugarcane (Saccharum officinarum) is a classic $C_4$ monocot grass exhibiting specialized Kranz leaf anatomy (concentric mesophyll cells encircling thick-walled, chloroplast-rich bundle sheath cells).
Statement B (Incorrect): Pineapple (Ananas comosus, Bromeliaceae) is an obligate Crassulacean Acid Metabolism (CAM) plant that opens stomata at night, not a $C_4$ plant.
Statement C (Correct): Mulberry (Morus alba) utilizes standard $C_3$ photosynthetic pathway.
Statement D (Correct): Sunflower (Helianthus annuus) is a classic $C_3$ dicotyledonous crop.

In 1955, Carlos Miller, Folke Skoog, and coworkers isolated the first cytokinin, named Kinetin (6-furfurylaminopurine), from degraded, autoclaved herring sperm DNA. Kinetin is an adenine derivative formed through the degradation of deoxyadenosine in the presence of furfural, and was found to powerfully stimulate cell division (cytokinesis) in tobacco pith tissue culture in the presence of auxin.

Correct intracellular compartmentation:

• Glycolysis (EMP pathway): Operates in the Cytosol/Cytoplasm of the cell -> (IV)
• Citric Acid Cycle (TCA / Krebs cycle): Located in the soluble aqueous Mitochondrial Matrix -> (I)
• $F_0-F_1$ ATP synthase: Embedded within the cristae of the Inner Mitochondrial Membrane (and chloroplast thylakoids) -> (III)
• Calvin Cycle ($C_3$ carbon fixation): Operates in the aqueous Stroma of Chloroplasts -> (II)

Thylakoid membranes in chloroplasts contain four major multiprotein complexes: Photosystem II (with its lumenal Oxygen Evolving Complex, OEC), Cytochrome $b_6f$ complex, Photosystem I, and $CF_0-CF_1$ ATP synthase, alongside Light-Harvesting Complexes (LHC I and LHC II). Alternative Oxidase (AOX) is a mitochondrial terminal oxidase localized in the inner mitochondrial membrane of plants and fungi that mediates cyanide-resistant alternative respiration, bypassing proton-pumping complexes III and IV. Hence, AOX is not a thylakoid membrane protein.