Plant tissue culture additive — role of silver thiosulfate (STS) In plant cell and micropropagation media, why is silver thiosulfate commonly added to the culture vessel or medium?

Introduction / Context:
Silver thiosulfate (STS) is a widely used supplement in plant tissue culture and micropropagation. In sealed vessels, explants often accumulate ethylene, a gaseous plant hormone that can inhibit growth, induce abscission, or cause vitrification. Understanding why STS is used helps practitioners prevent culture decline and improve morphogenesis.

Given Data / Assumptions:

• Cultures are maintained in closed or semi-closed containers.
• Ethylene accumulates readily in limited headspace.
• STS releases Ag+ ions complexed with thiosulfate.
• Goal: identify the principal reason for adding STS.

Concept / Approach:

Ethylene perception in plants occurs at membrane-bound receptors that require a transition metal cofactor. Silver ions (Ag+) competitively inhibit ethylene binding at these receptors, effectively blocking ethylene signaling. In sealed culture systems, suppressing ethylene action prevents callus browning, leaf abscission, shoot fasciation, and other stress symptoms that compromise regeneration.

Step-by-Step Solution:

Verification / Alternative check:

Protocols for ornamentals, potato, and woody plants frequently include STS dips or medium supplements to reduce ethylene response, improving shoot elongation and reducing leaf drop.

Why Other Options Are Wrong:

pH maintenance is typically achieved with buffers (e.g., MES) and by adjusting salts, not by STS. Phenolic removal is aided by activated charcoal or antioxidants, not STS. Increasing dissolved oxygen chemically is not STS’s role.

Common Pitfalls:

Confusing inhibition of ethylene biosynthesis with inhibition of ethylene action. STS primarily blocks perception/action, yet functionally it suppresses ethylene’s effects in culture.

Final Answer:

To block ethylene (C2H4) action and thereby prevent harmful ethylene build-up in closed cultures