Nurse/conditioned medium — identify the incorrect statement about its preparation and use

Introduction / Context:
Nurse or conditioned medium is a proven strategy to improve survival and regeneration of delicate cells such as protoplasts. It harnesses extracellular factors secreted by fast-growing cells. Recognizing correct handling is critical to maintain activity.

Given Data / Assumptions:

• Conditioned medium is harvested from actively dividing suspension cultures.
• Secreted molecules may be heat-labile proteins or small metabolites.
• Sterility must be ensured without degrading active factors.

Concept / Approach:

Because many components of conditioned media are heat-labile, autoclaving would denature or destroy them. Therefore, the accepted practice is to collect the medium aseptically and sterilize it by membrane filtration (e.g., 0.22 μm), not by autoclaving. It is then used alone or mixed with fresh medium to aid difficult cultures.

Step-by-Step Solution:

Verification / Alternative check:

Standard protocols for protoplast culture recommend filter-sterilized conditioned medium (or co-culture with feeder layers) to maintain bioactivity.

Why Other Options Are Wrong:

Options a, b, c, and e match accepted definitions and practices; they accurately describe source, content, application, and sterilization method (filtration).

Common Pitfalls:

Autoclaving “to be safe” compromises the very factors that make conditioned medium effective.

Final Answer:

It is removed aseptically and then autoclaved before use to ensure sterility