Correct Answer: (4) Antibiotics

For transgenic shoot selection in plant tissue culture, antibiotics are added to the medium to kill non-transformed cells while allowing only those with antibiotic resistance genes (like nptII for kanamycin) from the transgene to survive and regenerate.

Option Analysis

• (1) Vitamins: Incorrect. Vitamins support general growth as organic supplements but aren’t used for selecting transgenic shoots, as they don’t distinguish transformed from non-transformed cells.​

• (2) Carbohydrates: Incorrect. Carbohydrates like sucrose act as carbon sources and osmotic agents for basic metabolism in all cells, not for selective pressure against non-transgenics.​

• (3) Minerals: Incorrect. Minerals (inorganic salts like MS basal medium) provide essential nutrients for all explants but lack specificity to eliminate untransformed tissue.​

• (4) Antibiotics: Correct. Selectable markers confer resistance (e.g., kanamycin, hygromycin); antibiotics kill sensitive non-transgenic cells, ensuring only transgenic shoots proliferate.

Transgenic shoots selection medium relies on antibiotics to identify and grow only genetically modified plants in biotechnology protocols. This is crucial for plant molecular biology exams like GATE Life Sciences.​

Selection Mechanism

Antibiotic resistance genes (e.g., bar for Basta) in T-DNA allow transgenic cells to survive on selective media, while non-transgenic cells die from antibiotics like kanamycin or glufosinate. MS medium is typically supplemented post-Agrobacterium transformation.

Protocol Overview

Explants are cultured on callus induction medium, then transferred to selection medium with antibiotics (25-100 mg/L) plus hormones like BAP for shoot regeneration. Confirmed transgenics show resistance and are verified by PCR/GUS.

Common Antibiotics vs. Alternatives

Exam Relevance

Mastering this differentiates basic media components from selection agents, key for questions on plant transformation efficiency.​