Q.49 Which of the following tissue types is/are established during embryogenesis in
wild–type Arabidopsis thaliana?
(A) Shoot apical meristem
(B) Rosette leaf primordium
(C) Procambium
(D) Lateral root primordium

Shoot apical meristem (SAM) and procambium establish during embryogenesis in wild-type Arabidopsis thaliana.

SAM forms from upper tier cells in the globular stage through genes like WUSCHEL and SHOOTMERISTEMLESS. Procambium arises as elongated central cells in the lower tier during late globular stage via auxin signaling and MONOPTEROS.

Option Analysis

Shoot Apical Meristem (A): Correct. SAM precursors emerge at the 16-cell stage in the apical domain, becoming a three-layered structure by late heart stage between cotyledon primordia.

Rosette Leaf Primordium (B): Incorrect. Rosette leaves form postembryonically from the SAM during the vegetative phase after germination.

Procambium (C): Correct. Vascular procambium initials specify in the globular embryo’s central cylinder through oriented divisions and auxin transport via PIN1.

Lateral Root Primordium (D): Incorrect. Lateral roots initiate postembryonically from pericycle cells in the primary root after seedling establishment.

Arabidopsis Embryogenesis Stages

Arabidopsis follows the Onagrad-type pattern: zygote asymmetry yields apical (shoot) and basal (root/suspensor) lineages. Globular stage axializes via protoderm separation and procambial elongation; heart stage specifies SAM and cotyledons.

Key events:

• Octant: Upper/lower tiers form.

• Globular: Procambium and SAM precursors.

• Heart/Torpedo: Tissue maturation.

Tissue types established during embryogenesis in wild-type Arabidopsis thaliana represent foundational events in plant developmental biology. This process creates the seedling’s core pattern, including meristems and vascular tissues, through precise cell divisions and signaling.

Core Tissues Formed in Embryo

During globular-to-heart stages, shoot apical meristem precursors arise from upper-tier cells, marked by WUS and STM expression for postembryonic shoot growth. Procambium, the vascular precursor, elongates centrally via auxin gradients and MP/ARF5, forming stele strands.

Protoderm (epidermis) separates early via tangential divisions, while ground tissue precursors surround procambium radially.

Post-Embryonic Structures

Rosette leaf primordia emerge from SAM after germination in the vegetative rosette phase. Lateral root primordia initiate from xylem-pole pericycle in mature roots via auxin oscillations.

Molecular Mechanisms

Auxin transport via PIN proteins creates response maxima for procambium and SAM positioning. WOX genes establish apical-basal polarity from zygote asymmetry.

Answer: A and C suit CSIR NET preparation on Arabidopsis embryogenesis tissue patterning.