Plant Physiology- ICAR JRF/SRF 2024

• Pollen Dimorphism in Androgenesis: During anther and microspore culture, microspores differentiate into two physiological populations:
• S-grains (Sporophytic pollen grains): Smaller, poorly vacuolated, starched microspores with non-committed cytoplasm that respond preferentially by dividing symmetrically to initiate haploid embryogenesis.
• P-grains (Pollen grains): Normal gametophytic microspores committed to terminal pollen maturation that fail to undergo androgenic embryogenesis.

Correct option: (1) S-grains

• Assertion (A) is True: Hybrid embryo rescue (excising immature embryos and culturing them in nutrient media in vitro) is a cornerstone technique for overcoming post-zygotic barriers in wide/interspecific hybridization.
• Reason (R) is True & Explains (A): Interspecific crosses frequently trigger somatoplastic sterility, wherein the hybrid endosperm fails to develop properly and degenerates early, starving the developing hybrid embryo and causing seed abortion unless rescued in time.
• 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)

• Rice Chromosome Number: Cultivated rice (Oryza sativa) is a diploid species with $2n = 2x = 24$ chromosomes.
• Meiotic S-phase & Chromatid Count: Prior to entering Prophase I of Meiosis I, the cell completes interphase DNA replication. Consequently, each of the 24 chromosomes consists of two identical sister chromatids joined at the centromere.
• Calculation:

Correct option: (3) 48