Question

Which of the following is used for the visual assessment of percentage viability of protoplasts?

• A. Fluorescein diacetate
• B. Myo-inositol
• C. Biotin
• D. Sodium molybadate

Hint:

FDA Test = Green Glow. If the cell's "engine" (enzymes) is running and the "walls" (membrane) are intact, it will light up!

Answer 1

The Correct Option is A

Concept: Protoplasts are extremely fragile. After isolation, it is essential to determine what percentage of them are alive and metabolically active before proceeding with culture or fusion experiments.

Step 1: Mechanism of the FDA Test.
Fluorescein diacetate (FDA) (1) is a non-fluorescent, non-polar dye that can cross the plasma membrane. Inside a living cell, active esterase enzymes cleave the acetate groups, releasing fluorescein, which is polar and fluorescent.

Step 2: Visual Assessment.
Because the resulting fluorescein is polar, it cannot leak back out of an intact plasma membrane. When viewed under a fluorescence microscope, living protoplasts glow bright green, while dead or damaged cells remain dark. This allows for a quick and accurate visual count of viable cells.

Step 3: Evaluating Others.
Myo-inositol (2) and Biotin (3) are nutrients/vitamins used in growth media. Sodium molybdate (4) is a micronutrient. None of these have staining properties for viability assessment.