Question

Which group of phytohormone in plants is used for shoot multiplication under in vitro conditions?

• A. Auxin
• B. Cytokinin
• C. GA\(_3\)
• D. Abscisic Acid

Hint:

• Cytokinins Promote cell division and shoot formation. Key for shoot multiplication in micropropagation.
• Auxins Promote root formation and cell elongation.
• The auxin:cytokinin ratio is crucial for morphogenesis in plant tissue culture.

Answer 1

The Correct Option is B

Plant tissue culture involves growing plant cells, tissues, or organs in a sterile nutrient medium under controlled environmental conditions (in vitro). Phytohormones (plant hormones) play a crucial role in controlling growth and differentiation. For shoot multiplication (also known as shoot proliferation or axillary bud proliferation) in vitro, cytokinins are the primary group of phytohormones used.

• Cytokinins (e.g., Kinetin, Benzylaminopurine (BAP), Zeatin, Thidiazuron (TDZ)): Promote cell division (cytokinesis), shoot formation, and axillary bud development. They are essential for inducing multiple shoots from explants in micropropagation.
• Auxins (e.g., Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA), Naphthaleneacetic acid (NAA)): Primarily promote root formation (rhizogenesis), cell elongation, and apical dominance. They are also involved in callus formation.
• GA\(_3\) (Gibberellic Acid, a type of Gibberellin): Promote stem elongation, seed germination, and flowering. Sometimes used in tissue culture but not the primary hormone for shoot multiplication itself.
• Abscisic Acid (ABA): Generally a growth inhibitor, involved in stress responses, dormancy, and abscission. Not used for shoot multiplication.

The ratio of auxins to cytokinins is critical in determining the type of development in plant tissue culture:

• High cytokinin to auxin ratio: Favors shoot development.
• High auxin to cytokinin ratio: Favors root development.
• Intermediate ratio: Favors callus (undifferentiated cell mass) proliferation.

Therefore, cytokinins are used for shoot multiplication. \[ \boxed{\text{Cytokinin}} \]