1. Definitions

• Somatic Embryogenesis: The process where somatic (non-germline) cells develop into structures resembling zygotic embryos. These structures pass through recognizable embryonic stages (globular, heart, torpedo, cotyledon) and can germinate into full plants.

• Organogenesis: Formation of specific organs—either shoots or roots—from explants or callus tissue. It may occur:

  • Directly from explants (direct organogenesis)

  • Indirectly from callus tissue (indirect organogenesis)

2. Why Are These Techniques Important?

These two regeneration methods:

• Enable regrowth after transformation

• Are more efficient than micropropagation in some species

• Allow long-term storage of regenerable callus or embryos

• Support genetic screening, cryopreservation, and artificial seed production

📌 Somatic Embryogenesis Review

3. Hormonal Regulation

The interplay of auxins and cytokinins controls cell fate:

Common PGRs:

• Auxins: 2,4-D (callus/embryo), NAA, IAA

• Cytokinins: BAP, Zeatin, TDZ (shoots)

Some protocols use a 2,4-D induction phase, followed by growth regulator-free media for embryo maturation.

4. Process of Somatic Embryogenesis

Stages:

1. Induction (high auxin)

2. Globular embryo stage

3. Heart-shaped

4. Torpedo-shaped

5. Cotyledon stage

6. Germination and conversion to plantlets

📌 Embryogenesis in Plant Tissue Culture

5. Direct vs. Indirect Organogenesis

• Direct: Tissues form organs without intermediary callus

  • Faster

  • Less prone to mutations

• Indirect: Goes through callus stage

  • More flexible

  • Higher risk of somaclonal variation

Applications:

• Regeneration after gene editing

• Propagation from leaf or cotyledon tissues

• Recovery of traits from mutant or treated lines