Question

Which is the correct sequence of different stages of embryo development in plants?

• A. Fertilization, Zygote, Globular stage, Heart stage, Torpedo stage
• B. Fertilization, Zygote, Heart stage, Torpedo stage, Globular stage
• C. Fertilization, Zygote, Globular stage, Torpedo stage, Heart stage
• D. Zygote, Fertilization, Globular stage, Torpedo stage, Heart stage

Hint:

To easily remember the sequence, visualize the geometric progression of the embryo's shape:
Single cell (Zygote) $\rightarrow$ Sphere (Globular) $\rightarrow$ Two lobes (Heart) $\rightarrow$ Cylinder (Torpedo).

Answer 1

The Correct Option is A

Plant embryogenesis is the process that initiates after the double fertilization of an ovule, leading to the development of a fully structured plant embryo.
The development of the plant embryo in dicotyledonous species follows a highly coordinated and structurally distinct series of morphological stages.
These stages are characterized by changes in cell division patterns, tissue layer differentiation, and structural symmetry.

Step 2: Detailed Explanation:
The embryonic development of a dicot plant proceeds through the following sequential milestones:
1. Fertilization: This is the initial event where the haploid male gamete from the pollen tube fuses with the haploid female egg cell inside the embryo sac to form a diploid entity.
2. Zygote: The immediate cellular product of fertilization is the single-celled diploid zygote. The zygote undergoes an asymmetric transverse division, giving rise to a small apical cell (which forms the embryo proper) and a large basal cell (which forms the suspensor).
3. Globular Stage: The apical cell undergoes a series of ordered, symmetric divisions to form a spherical mass of cells. At this stage, the embryo exhibits radial symmetry, and the primary tissue layers (protoderm, ground meristem, and procambium) begin to differentiate.
4. Heart Stage: As cell division concentrates in two localized regions of the globular embryo, the primordia of the two cotyledons begin to form. This localized growth transforms the spherical shape into a heart-like structure, marking the transition from radial to bilateral symmetry.
5. Torpedo Stage: Continual cell elongation and division along the embryonic axis cause the cotyledons and the hypocotyl to lengthen. The embryo assumes an elongated, torpedo-like shape. Following this, the embryo matures and dehydrates, entering a dormant state within the seed.
Comparing these steps with the given options, we can see that Option (A) presents the correct chronological sequence of plant embryogenesis.

Step 3: Final Answer:
The correct developmental sequence is: Fertilization $\rightarrow$ Zygote $\rightarrow$ Globular stage $\rightarrow$ Heart stage $\rightarrow$ Torpedo stage.