30. Following statements are made in relation to the five widely recognized stages of Arabidopsis embryogenesis:
    A. The fusion of haploid egg and sperm takes place in globular stage
    B. Rapid cell division in two regions on either side of the future shoot apex forms heart stage
    C. The cell elongation throughout the embryo axis and further development result in torpedo stage
    D. The embryo loses water and becomes metabolically inactive in the zygotic stage
    Which combination of the above statements is correct?
    (1) A and B (2) B and C
    (3) C and D (4) D and A

The correct combination of statements regarding the five widely recognized stages of Arabidopsis embryogenesis is:

(2) B and C

Explanation:

• (B) Rapid cell division in two regions on either side of the future shoot apex forms the heart stage — This is correct. The heart stage is characterized by the initiation of cotyledon primordia flanking the shoot apex, leading to the heart-shaped embryo.​

• (C) The cell elongation throughout the embryo axis and further development result in the torpedo stage — This is correct. The torpedo stage is marked by elongation along the embryonic axis and development of cotyledons and vascular tissues.​

• (A) The fusion of haploid egg and sperm takes place in globular stage — Incorrect. Fertilization occurs before embryogenesis begins; the globular stage is well after fusion and involves early cell division and pattern establishment.​

• (D) The embryo loses water and becomes metabolically inactive in the zygotic stage — Incorrect. The zygotic stage is the very beginning post-fertilization; embryo water loss and metabolic inactivity happen much later during seed maturation.​

Introduction

Arabidopsis embryogenesis proceeds through recognizable stages: zygote, globular, heart, torpedo, and mature embryo. Critical developmental events during the heart and torpedo stages notably shape the embryonic form, including cotyledon initiation and axis elongation.

Heart Stage Characteristics

• Defined by rapid cell divisions on either side of the shoot apical meristem forming two cotyledon primordia.​

• Embryo obtains a heart-shaped appearance, marking major organ initiation.​

• Shoot meristem region becomes anatomically distinct.​

Torpedo Stage Features

• Cells elongate extensively along the embryonic axis establishing length and basic morphology.​

• Cotyledons also grow and vascular tissues extend further.​

• Morphogenesis prepares the embryo for maturation and eventual germination.​

Contrasts with Other Stages

• Zygotic stage involves the fertilized egg prior to division.​

• Globular stage features early symmetric cell division but no cotyledon formation.​

• Maturation entails embryo dehydration and preparation for dormancy.​

Summary Table: Stages and Key Events in Arabidopsis Embryogenesis

Conclusion

The heart and torpedo stages encapsulate critical developmental activities in Arabidopsis embryogenesis like cotyledon formation and embryo elongation, respectively, making (2) the correct option.