The best way to preserve onion root tips for mitosis observation is to use an acetic ethanol fixative. This process will stop mitosis at the current stage, and preserve the cellular structures.
Preserving Onion Root Tips: A Step-by-Step Guide
Here's a detailed look at how to properly preserve onion root tips for studying mitosis:
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Root Growth: First, grow your onion roots in a suitable environment (e.g., in water). Wait until the roots are around 1-2 cm long for best results.
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Harvesting Root Tips: Carefully cut off the very tip (about 1-2 mm) of each root. The root tip is where active cell division (mitosis) occurs, which you are going to observe later.
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Fixation: Place the harvested root tips immediately into the acetic ethanol fixative solution. This fixative solution is typically a mixture of glacial acetic acid and ethanol. This solution serves two important purposes:
- It stops cell division at the current stage so you can see the different stages of mitosis.
- It preserves the cellular structure of the root tip, preventing degradation and allowing later staining.
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Storage: The root tips in the acetic ethanol fixative can be stored for at least two weeks before staining, without compromising the quality of the sample for later observation. Make sure the container is well-sealed and stored at room temperature.
Preparing Root Tips for Microscopy
After fixation, additional steps are required to prepare the root tips for examination under a microscope.
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Cell Wall Breakdown: Treat the fixed root tips with acid and heat. This treatment breaks down the cellulose cell walls and helps the stain penetrate into the tissue and makes it easier to squash the tissue on a microscope slide.
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Staining: Apply a suitable stain, such as aceto-orcein or Feulgen stain. The stains will bind to the chromosomes making them more visible under a microscope.
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Squashing: Place the stained root tip on a microscope slide, cover it with a coverslip, and carefully squash the tissue. This process will spread the cells to make them easier to see under the microscope.
Why this Method?
The described method is ideal because:
- Preservation: The acetic ethanol fixative effectively preserves the cellular structures, allowing for later detailed examination of the various stages of mitosis.
- Long-term Storage: The fixative enables you to store the root tips for a significant time (up to two weeks or even longer, depending on storage conditions) without altering the tissue.
- Enhanced Visualization: Acid treatment, along with the staining and squashing techniques, allows for clear and distinct visualization of chromosomes during the mitotic process.
| Step | Description | Purpose |
|---|---|---|
| 1 | Grow onion roots | Obtaining tissue undergoing mitosis |
| 2 | Cut off root tips | Isolating the region with the highest mitotic activity |
| 3 | Fix in acetic ethanol fixative | Stop cell division, preserve cellular structure |
| 4 | Storage in fixative | Enable long-term storage until further processing |
| 5 | Acid and Heat Treatment | Breaks cell walls |
| 6 | Staining | Enhance visualization of chromosomes |
| 7 | Squashing | Spreading the cells to allow for better microscopic observation |
