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Question #47721
The Question
A researcher constructs a recombinant Ti plasmid by inserting a pest-resistant gene into the T-DNA region, simultaneously utilizing the lacZ gene for blue-white screening. After successfully transforming Agrobacterium tumefaciens, they infect tobacco leaf discs. To verify successful T-DNA expression in the plant, the leaf discs are cultured on a medium containing X-gal. However, the screening fails to produce the expected blue/white differentiation in the plant tissue. What is the primary biological reason for this failure?
Options
- A.
The lacZ gene requires prokaryotic transcription-translation machinery and specific host complementation, which are absent in eukaryotic plant cells.
- B.
The T-DNA border sequences fail to recognize the prokaryotic lacZ gene, leading to its truncation during transfer by the VirD2 endonuclease.
- C.
Plant cells possess a highly acidic vacuolar pH that denatures the X-gal substrate before beta-galactosidase can cleave it.
- D.
Insertional inactivation of the lacZ gene prevents the formation of the T-complex, halting its nuclear localization in plant cells.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
pBR322 Selection Logic|Gel Electrophoresis Migration|Elution Process
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize 'Blue-White screening = Recombinant detection' without considering the host-specific nature of gene expression.
The trap lies in failing to distinguish between screening the intermediate bacterial vector (prokaryotic) and expressing the reporter in the final transgenic host (eukaryotic plant).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | pBR322 Selection Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |