Shoot develops in tissue culture when there is

Options

A. High gibberellin to cytokinin ratio
B. High gibberellin to auxin
C. High auxin to cytokinin ratio
D. High cytokinin to auxin ratio

Answer

To determine when a shoot develops in tissue culture, we need to understand the roles of different plant growth regulators (PGRs) involved in the process. Here’s a step-by-step solution:

### Step 1: Understanding Organogenesis
- Organogenesis is the process of forming organs (like shoots and roots) from undifferentiated cells (callus) in tissue culture.

### Step 2: Identifying Key Plant Growth Regulators
- The main PGRs involved in shoot and root development are auxins and cytokinins.
- Auxins generally promote root development, while cytokinins promote shoot development.

### Step 3: Analyzing the Ratios of PGRs
- The ratio of auxin to cytokinin is crucial:
- **High Auxin to Cytokinin Ratio**: Promotes root development.
- **High Cytokinin to Auxin Ratio**: Promotes shoot development.

### Step 4: Evaluating the Given Options
- The question provides several options regarding the ratios of gibberellin, auxin, and cytokinin:
1. High gibberellin to cytokinin ratio
2. High gibberellin to auxin ratio
3. High auxin to cytokinin ratio
4. High cytokinin to auxin ratio

### Step 5: Eliminating Incorrect Options
- **Options 1 and 2**: Both involve gibberellin, which is not directly responsible for shoot development in this context.
- **Option 3**: High auxin to cytokinin ratio promotes root development, not shoot development.

### Step 6: Selecting the Correct Answer
- **Option 4: High cytokinin to auxin ratio** is the correct answer because it promotes shoot development in tissue culture.

### Final Answer
- Shoot develops in tissue culture when there is a **high cytokinin to auxin ratio**.

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