Feeder support in regeneration — What is used when culturing regenerating protoplasts, single cells, or very dilute plant cell suspensions?

Introduction / Context:
Single plant cells and protoplasts are fragile and often require paracrine-like support to divide and regenerate. Nurse (feeder) systems provide conditioned media and/or living feeder cells that release hormones, peptides, and metabolites enhancing survival and morphogenesis.

Given Data / Assumptions:

• Protoplasts lack cell walls initially and are osmotically sensitive.
• Very low cell densities reduce autocrine/cell–cell signaling support.
• Feeder layers or conditioned media can supply diffusible stimuli.

Concept / Approach:
Both a “nurse medium” (conditioned by an actively growing culture) and a “nurse/feeder culture” (living cells separated by a membrane or co-cultured) serve the same purpose: supplying growth factors and stabilizing the microenvironment for regeneration.

Step-by-Step Solution:

Verification / Alternative check:
Empirical data show increased plating efficiency and colony formation when using nurse systems versus unsupported minimal media.

Why Other Options Are Wrong:

Common Pitfalls:
Skipping osmotic stabilizers (e.g., mannitol, sorbitol) and appropriate Ca/Mg can negate nurse benefits.

Final Answer:
Both (a) and (b).