Two transgenic plants are grown. One plant has a gene encoding a fluorescent pigment incorporated in its genome. The other plant has a fire fly luciferase gene incorporated in its genome. Which of the two plants will glow in the dark?

**Core Concept**
The question tests the understanding of **bioluminescence** and **fluorescence** in transgenic organisms. Bioluminescence is the production and emission of light by living organisms, whereas fluorescence is the absorption and re-emission of light at a different wavelength.

**Why the Correct Answer is Right**
The plant with the fire fly **luciferase** gene will glow in the dark because luciferase catalyzes a reaction that produces light, resulting in bioluminescence. This reaction involves the oxidation of **luciferin**, resulting in an excited state that releases energy as light when it returns to its ground state.

**Why Each Wrong Option is Incorrect**
**Option A:** A fluorescent pigment requires an external light source to absorb and re-emit light, so it will not glow in the dark without illumination.
**Option C and D:** Without specific details on what these options entail, the focus remains on the principle that bioluminescence, like that from luciferase, is necessary for glowing in the dark.

**Clinical Pearl / High-Yield Fact**
Remember that bioluminescence is a critical tool in molecular biology for reporting gene expression, and **luciferase** is commonly used for this purpose due to its ability to produce a detectable signal.

**Correct Answer:** D. The plant with the fire fly luciferase gene.

✓ Correct Answer: A. Both plants will glow