Stomata are the elliptical openings on leaves, guarded by two cells, which when swollen with water allow stomata to open and when flaccid allow stomata to close. The guard cells of the stomata possess large vacuoles, chloroplast, and nucleus. Stomata help the plant to take in carbon dioxide needed for photosynthesis. They look like tiny mouths opening and closing as they help in transpiration.
The bigger/wider the leaf, the greater the rate of transpiration as more surface means more stomata will be present. Plants possessing smaller stomata have lower levels of evaporation and survive harsh conditions better. All green plants are termed as producers as they produce their own food from solar energy, and carry out the vital processes of photosynthesis and respiration where gaseous exchange between the tissue of plants and the atmosphere is an essential component of the whole ecosystem. This is carried out through the tiny openings known as stomata.
A plant survives better with faster growth if it possesses a higher number of stomata and a wet climate. The lower the number of stomata, the lower the rate of photosynthesis, and a drier climate is not ideal for plant growth.
There are four types of stomata:
Moss Type: These are found in certain mosses.
Gymnospermous: These are naked seed plants deeply sunken to reduce water loss during transpiration.
Coniferous: Sunken stomata and the guard cells are elliptical.
Gramineous: These are found in grade families, two guard cells and two subsidiary cells are present too.
On the basis of arrangement, the types of stomata are:
Anomocytic Stomata - This type of stomata is embedded in the epidermal cells having fixed shape and size where there is no fixed number of cells surrounding the stomata.
Anisocytic Stomata - In this arrangement, three subsidiary unequal cells are surrounding the stomata.
Paracytic Stomata - Here the stomatal pore and guard cells surround the stomata.
Diacytic Stomata - It is surrounded by subsidiary cells lying perpendicular to the guard cells.
Gramineous Stomata - Stomata has two dumbbell shaped guard cells and subsidiary cells which lie parallel to guard cells.
Coniferous Stomata - It is found on the surface of the leaves of gymnosperm plants and is found below the leaf surface.
To prepare a temporary mount of a leaf peel to show stomata, we need to follow the correct method of arrangement. We need some essential equipment such as needles, forceps, watch glass, dropper, slides, coverslip, blotting paper, safranin, glycerine, and a compound microscope.
First and foremost, fold a leaf to pull apart and take the peel off the leaf from the lower surface. Peeling the leaf with a blade requires patience and dexterity. We must immediately dip the transparent peel off the leaf in water kept in watch glass to avoid shrinkage and crumpling. Let it remain in the water for a while and in the watch glass, add a few drops of glycerine so that the peel remains hydrated.
Let it rest, then add a few drops of safranin which are red in colour through a dropper. Now we take out the peel with the help of forceps and put it gently on the glass slide. We blot away the excess glycerin and safranin with blotting paper. On examination, under a compound microscope, we clearly observe the epidermal cells containing stomata on the lower surface of the leaf.
The epidermal cells are seen in an irregular manner with no intracellular space between them. Stomata and guard cells both are observed clearly on the surface. Guard cells possess a nucleus and chloroplasts too. They possess a thin outer and thick inner cover. The number of stomata is less compared to those found on the lower surface of the leaf. The reason behind this is to prevent excessive loss of water through evaporation which happens because of exposure to direct sunlight.
Leaf Observed Under Microscope
An interesting fact is that the stomata are studied during research if a plant has undergone any kind of stress due to excessive heat, drought, or any kind of harsh conditions.
1. What are light induced stomatal responses?
Ans: Light induced stomatal responses were first reported by Darwin (1989). Stomata open up in response to light that includes blue and red light. Red light makes it possible for stomata to open by photosynthesis in the guard cell chloroplasts. Blue light brings about stomatal opening. Phototropins in the guard cell act as receptors for blue light and opening of stomata.
2. Which hormone is responsible for stomatal colour?
Ans: The hormone which is responsible for the colour of stomata is abscisic acid. It is a plant hormone largely involved in the growth and development of the plant.
The peel should be cut to a proper size and kept hydrated with glycerine
A few drops of safranin help in magnifying the stomata and guard cells with ease.
A coverslip should be placed in such a manner as to avoid air bubbles.
Stomata are better seen on the lower surface of a dicot leaf
1. Why is glycerine used for the preparation of a temporary mount of leaf peel?
Glycerine is a good hydrating agent and prevents the leaf peel from crumpling and drying. An additional benefit of using glycerine is its refractive property as it reflects light better for our observation. The peel appears clearer, shinier, and clearly observed. Glycerin possesses the same concentration as the cell sap due to which the cells in the leaf peel mounted on the slide will neither be flaccid or turgid and can be observed in their natural form.
2. Is there any specific colour of stomata?
Guard cells that flank the stomata are kidney-shaped and are green in colour as they contain chlorophyll, while the epidermal cells are chlorophyll-free and contain Red pigment. Red light helps stomatal opening by the process of photosynthesis. So they are tiny openings found on aerial parts particularly leaves that appear green in colour. Interestingly, different coloured petals of flowers often have stomata that are sometimes non-functional. Fruits also can possess stomata. Abscisic acid is a plant hormone that influences the colour of stomata.
3. What is lamina?
Lamina is an expanded part of a leaf that contains chloroplasts. Its structure which catches hold of the base from the stem is kind of a thin plate or a layer that is generally broad and flat. It's vital as photosynthesis depends on it and also helps chloroplast cells to penetrate and absorb light from the atmosphere. The leaf blade is the structural part of the plant, whereas the lamina of the leaf is the flat region that contains the chloroplast, veins, and stomata.