Some of the cytokinins used in plant tissue culture media are given below:
[P] BAP
IQI Zeatin
[R] Kinetin
[S] 2iP
Which of these are synthetic analogs?
Options:
(A) P and Q only
(B) Q and S only
(C) R and S only
(0)
P and R only
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.42)**
**1. Governing Concept**:
- **Topic**: Plant Biotechnology & Synthetic Phytohormones
- Cytokinins used in plant tissue culture:
- **Adenine-derived (isoprenoid / aromatic) cytokinins**:
- **Kinetin** ($N^6$-furfuryladenine)
- **Zeatin** (natural isoprenoid cytokinin)
- **6-Benzylaminopurine (BAP / BA)** ($N^6$-benzyladenine)
- **Phenylurea-derived cytokinins**:
- **Thidiazuron (TDZ)** (chemically a substituted phenylurea, 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea, that exhibits potent cytokinin-like organogenic activity).
- Hence, cytokinins include both purine (adenine-type) and substituted urea derivatives.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Incomplete chemical classification.
- **Option (B) is INCORRECT**: Excludes phenylurea types.
- **Option (C) is INCORRECT**: Distorts structural groups.
- **Option (D) is CORRECT**: Accurately classifies adenine-type and urea-derived cytokinins.
**3. Final Answer**:
- **Correct Choice**: **D**
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