Difference Between Guard Cells and Subsidiary Cells

Main Difference – Guard Cells vs Subsidiary Cells

Guard cells and subsidiary cells are found in the plant epidermis, surrounding the stoma. The epidermis of plants consists of a waxy cuticle, which acts as a protective barrier against water loss, mechanical injury, and infections. Stomata are the pores involved in the gas exchange of plants with the external environment. Water is also lost from the plant in the form of water vapor through stomata, generating an upward force on the water in the xylem. Opening and closing of the stoma are regulated by regulating the water potential inside the guard cells. The main difference between guard cells and subsidiary cells is that guard cells are found in the epidermis of the plant, forming stoma whereas subsidiary cells are found surrounding guard cells, assisting in the functioning of guard cells. 

This article explores,

1. What are Guard Cells
      – Characteristics, Structure, Function
2. What are Subsidiary Cells
      – Characteristics, Structure, Function
3. What is the difference between Guard Cells and Subsidiary Cells

What are Guard Cells           

Guard cells are a type of epidermal cells in plants; a pair of guard cells are involved in the formation of the stoma. The stoma is a hole found on the underside of the plant leaf; this helps in the gas exchange between leaf and the external environment. The gasses involved in photosynthesis, oxygen and carbon dioxide, are exchanged through stomata. Guard cells are found in the epidermis of leaves and stems of plants. They are specialized parenchyma cells, which are the only photosynthesizing cells found in the plant epidermis. The opening and closing of the stomatal pore are regulated by the water potential inside guard cells. When water is readily available, guard cells become turgid, opening the stomatal pore. When water is not available in hot and dry conditions, guard cells become flaccid, closing the stomatal pore. Water potential inside guard cells is controlled by controlling the solute exchange in and out of the guard cell. Water loss from the plant is called transpiration, which also occurs through stomatal pores. Transpiration produces a pull on water in the xylem to move upwards inside the stem. It also allows cooling of the plant body. A pair of guard cells which forms the stomatal pore between the two cells is shown in figure 1.

Figure 1: A pair of guard cells

What are Subsidiary Cells

Subsidiary cells are the accessory cells to guard cells in the epidermis of plants. Two or four subsidiary cells are found surrounding the pair of guard cells. Subsidiary cells do not consist of chloroplasts. They provide support for the functioning of guard cells in the epidermis. Subsidiary cells play a role in ion channel-mediated opening and closing of guard cells. They also separate a pair of guard cells from other guard cells in the epidermis. Subsidiary cells contain papillae, which arches across the stoma. The arch creates a mini-depression. It controls the escaping of water through the stoma by giving time to diffuse back into the stoma. Otherwise, water will be immediately blown away by a breeze. Three types of formation of subsidiary cells, surrounding guard cells can be observed: anisocytic, paracytic or diacytic. The unequal arrangement of subsidiary cells, surrounding guard cells is called anisocytic arrangement of subsidiary cells. The arrangement of subsidiary cells along the long axis of the guard cells is called paracytic arrangement of subsidiary cells. The arrangement of subsidiary cells in the right angle to the guard cells is called diacytic arrangement of subsidiary cells. Subsidiary cells, surrounding the two guard cells are shown in figure 2.

Figure 2: Subsidiary cells and guard cells

Difference Between Guard Cells and Subsidiary Cells

Correspondence

Guard Cells: Guard cells are found in the epidermis of plants, forming the stomata.

Subsidiary Cells: Subsidiary cells are found surrounding guard cells, providing the support to guard cells.

Arrangements

Guard Cells: Guard cells are arranged in pairs, surrounding the stomata.

Subsidiary Cells: Subsidiary cells are arranged surrounding guard cells in anisocytic, paracytic or diacytic format.

Function

Guard Cells: Guard cell regulate the opening and closing of their stomata.

Subsidiary Cells: Subsidiary cells assist, reinforce or protect guard cells.

Chloroplasts

Guard Cells: Guard cells contain chloroplasts.

Subsidiary Cells: Subsidiary cells do not contain chloroplasts.

Conclusion

Guard cells and subsidiary cells are two types of differentiated cell types found in the epidermal tissue of plants. Other two types of cells found in the plant epidermis are epidermal cells and epidermal hairs. Guard cells are the only photosynthesizing cells found in the epidermis. They form the stomatal pore in the epidermis by arranging in pairs. The stomatal pore is responsible for the gas exchange of the plant with the external environment. Carbon dioxide and oxygen, which are the gasses involved in the photosynthesis are exchanged through the stomatal pore. Transpiration also occurs through stomatal pores. The rate of photosynthesis depends on the opening and closing of the stomatal pore. The size of the stomatal pore is controlled by the water potential inside the guard cell. Subsidiary cells are accessory cells, which assist the functioning of guard cells. They are involved in the ion channel-mediated opening and closing of guard cells. Subsidiary cells are involved in the prevention of water loss from the stoma as well. The main difference between guard cells and subsidiary cells is their structure on the plant epidermis.

Reference:
1. Stomata, Subsidiary Cells, and Implications. N.p., n.d. Web. 25 Apr. 2017.
2. Glover, Beverley J. “Differentiation in plant epidermal cells.” Journal of Experimental Botany. Oxford University Press, 01 Mar. 2000. Web. 25 Apr. 2017.

Image Courtesy:
1. “Plant stoma guard cells” By (Image: Alex Costa) – Protein Kinases and Plant Pores. Gross L, PLoS Biology Vol. 4/10/2006, e358 http://dx.doi.org/10.1371/journal.pbio.0040358 ( CC 表示 2.5) via Commons Wikimedia
2. “Stomata” by AJC1 (CC BY-SA 2.0) via Flickr