The key difference between guard cells and subsidiary cells in plants is that guard cells are the specialized parenchyma cells that enclose stomata present in the epidermis of leaves, stems, etc. while subsidiary cells are the surrounding supportive cells of guard cells.
Stomata are the pores located in plant epidermis that facilitate the gaseous exchange. Two guard cells surround and regulate the size of a stoma. These guard cells are specialized parenchyma cells. There is another type of cells called subsidiary cells in the plants. Subsidiary cells support the guard cells by surrounding them. Both guard cells and subsidiary cells are important cell types in the function of the stomata in plants. Hence, this article focuses on discussing the difference between guard cells and subsidiary cells.
CONTENTS
1. Overview and Key Difference
2. What are Guard Cells
3. What are Subsidiary Cells
4. Similarities Between Guard Cells and Subsidiary Cells
5. Side by Side Comparison – Guard Cells vs Subsidiary Cells in Tabular Form
6. Summary
What are Guard Cells?
Guard cells are specialized cells found in the epidermis of leaves, stem and other organs of plants. Guard cells fulfil a special function in surrounding and regulating the size of stomata. Stomata are the pores that facilitate the gaseous exchange in plants. There are two guard cells around a stoma. Many stomata are present in the lower epidermis of leaves. Hence, there are many guard cells in the lower epidermis of leaves.
Guard cells regulate the opening and closing of stomata at the right time, especially during photosynthesis. It is done by maintaining a constant water potential gradient in the guard cells. In the presence of a high water potential inside the guard cells, the guard cells become highly turgid. Thus, this results in the opening of the stoma pore. In contrast, during the presence of a low water potential inside the guard cells, the guard cells are less turgid. Hence, this results in the closing of the stoma pore. The regulation of the water potential inside the guard cells takes place through the solute exchange in and out of the guard cells.
Figure 01: Guard Cells
Guard cells are specialized parenchyma cells. Therefore, they have the ability to photosynthesize and store food as starch. They also regulate the rate of transpiration in plants. Transpiration pull will facilitate the movement of water up the xylem vessels while cooling the plant.
What are Subsidiary Cells?
Subsidiary cells are the cells surrounding the guard cells. They are distributed in the epidermis of the plant leaf or stems. There are two or four rounds of subsidiary cells surrounding the guard cells. They are non-photosynthetic cells as they lack chloroplasts. The main function of subsidiary cells is to provide strength and to facilitate the function of the guard cells. In this regard, they control the movement of ions across the guard cells. In addition, subsidiary cells form the boundary separation between two guard cells.
Figure 02: Subsidiary Cells
There are different types of subsidiary cells. They are anisocytic, paracytic and diacytic. In each of these three types, the arrangement of the subsidiary cells differs. Anisocytic arrangement has subsidiary cells forming unequally around the guard cells. Paracytic arrangement has subsidiary cells forming along the long axis of the guard cells while diacytic arrangement has subsidiary cells forming in right angles to the guard cells.
What are the Similarities Between Guard Cells and Subsidiary Cells?
- Guard cells and subsidiary cells are two components of the stomatal apparatus.
- Both cell types are found in the epidermis of the leaves, stem and other organs of the plant.
- Also, both are living cells.
- Moreover, both cells control the stomata function; in turn, they control the gaseous exchange of plants.
- Besides, both cells play an active role in transpiration, movement of water, and taking part in osmosis during plant processes.
What is the Difference Between Guard Cells and Subsidiary Cells?
Guard cells and subsidiary cells are two important cell types associating stomata of plants. The key difference between guard cells and subsidiary cells is in the distribution. Guard cells surround the stomata while the subsidiary cells surround the guard cells. Furthermore, around one stoma, there are two guard cells. But, around one stoma, there are two to four rounds of subsidiary cells surrounding two guard cells. So,this is also a difference between guard cells and subsidiary cells.
Moreover, another significant difference between guard cells and subsidiary cells is the presence and absence of chloroplasts. Guard cells contain chloroplasts and can photosynthesize while subsidiary cells lack chloroplasts; hence, they cannot photosynthesize.
Summary – Guard Cells vs Subsidiary Cells
Guard cells and subsidiary cells are mainly present in the epidermis of plant leaves. They are derived from the epidermal cells. In summarizing the difference between guard cells and subsidiary cells, guard cells surround the stomata and regulate the stomatal pore activity while subsidiary cells surround the guard cells, providing strength and protection for the functions of the guard cells. Together, both guard cells and subsidiary cells regulate the transpiration in plants.
Reference:
1.Franks, Peter J, and Graham D Farquhar. “The Mechanical Diversity of Stomata and Its Significance in Gas-Exchange Control.” Plant Physiology, American Society of Plant Biologists, Jan. 2007, Available here.
Image Courtesy:
1. “Opening and Closing of Stoma” By Ali Zifan – Own work; Used information from:Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman.and [1] (CC BY-SA 4.0) via Commons Wikimedia
2. “Image from page 61 of “Comparative anatomy of the vegetative organs of the phanerogams and ferns;” (1884)” By Internet Archive Book Images (No known copyright restrictions) via Flickr