Plant growth regulators — which hormone class directly promotes cell division in culture?

Introduction / Context:
Successful plant tissue culture relies on balancing plant growth regulators (PGRs). While several hormones influence growth, one class is classically associated with stimulating cytokinesis (cell division), shoot organogenesis, and bud proliferation.

Given Data / Assumptions:

• We refer to standard in vitro conditions (e.g., MS medium).
• Common PGRs include auxins, cytokinins, gibberellins, brassinosteroids, and abscisic acid.
• We seek the hormone class that directly promotes cell division.

Concept / Approach:

Cytokinins (e.g., BAP/BA, kinetin, TDZ, zeatin) promote DNA synthesis and cytokinesis, driving shoot initiation and proliferation. Auxins (e.g., IAA, NAA, IBA, 2,4-D) promote cell expansion, callusing, and rooting; high auxin with low cytokinin favors roots or callus, whereas higher cytokinin with lower auxin favors shoots. Gibberellins mainly elongate stems and break dormancy; brassinosteroids modulate growth and stress responses; abscisic acid typically promotes maturation or stress tolerance and inhibits division.

Step-by-Step Solution:

Verification / Alternative check:

Textbook organogenesis rules: high cytokinin/low auxin → shoots; high auxin/low cytokinin → roots/callus, confirming cytokinins drive cell division for shoot formation.

Why Other Options Are Wrong:

Auxins primarily influence elongation, rooting, and callus induction. Gibberellins elongate internodes but do not primarily drive mitosis in culture. Brassinosteroids are growth modulators, not the main division driver. Abscisic acid inhibits division and promotes maturation.

Common Pitfalls:

Assuming “more growth” equals “more division.” Some PGRs elongate cells without increasing mitotic events.

Final Answer:

Cytokinins