Measuring Stomatal Density on Leaf Surfaces
Definition
Stomata
Stomata are small openings on the leaf surface that regulate gas exchange and water loss in plants
- Stomatal density refers to the number of stomata per unit area of a leaf surface.To determine this, the number of stomata in a known area must be counted using a microscope.
- Guard cells and stomata are microscopic, making them invisible to the naked eye but easily visible with proper tools.
Techniques for Measuring Stomatal Density
1. Peeling the Epidermis
- A section of the epidermis (outer leaf layer) is peeled off.
- Steps:
- Fold the leaf to break tissues apart from the lower epidermis.
- Carefully peel off the epidermis or tear the leaf diagonally to expose epidermal sections.
- Mount the epidermis in water on a microscope slide.
- Suitable Species: This method works well for plants like Commelina and Tradescantia.
Experiment with different plant species to refine this peeling technique
2. Using Nail Varnish
- Works best for smooth, non-hairy leaves.
- Steps:
- Apply colourless nail varnish to the leaf's upper and lower surfaces.
- Once dry, peel off the varnish to form a leaf cast.
- Mount the cast on a microscope slide for examination.
The nail varnish method produces a clear impression of stomata and cell margins, allowing easy visualization under a microscope
Observing and Counting Stomata
- Place the peel or cast under the microscope.
- Adjust the slide until the field of view is fully filled.
- Count the number of stomata in the field of view.
- Repeat counts across multiple fields to calculate an average stomatal number.
- Accurate results require multiple counts and consistent microscope adjustments
- Take this into account whenever you're analyzing data sets.
Calculating Stomatal Density
- To calculate stomatal density (mm⁻²):
$$
\text{Stomatal Density (mm}^{-2}\text{)} = \frac{\text{Mean Number of Stomata}}{\text{Area of Field of View (mm}^2\text{)}}
$$
Consider how stomatal density vary between different types of plants, such as aquatic and desert species, and why?
