Guard Cells vs. Subsidiary Cells

Attribute	Guard Cells	Subsidiary Cells
Location	Epidermis of plant leaves and stems	Found adjacent to guard cells in the epidermis
Shape	Bean-shaped	Varies depending on the plant species
Function	Regulate the opening and closing of stomata	Provide support and assist in the movement of guard cells
Cell Wall Thickness	Thin	Thicker than guard cells
Chloroplasts	Present in some species	Usually absent
Cell Division	Rarely divide	Capable of division

Introduction

Guard cells and subsidiary cells are two types of specialized cells found in the epidermis of plant leaves. They play crucial roles in regulating the movement of gases, such as carbon dioxide and oxygen, as well as the loss of water through stomata. While both cell types are involved in the same process, they possess distinct attributes that contribute to their specific functions. In this article, we will explore and compare the characteristics of guard cells and subsidiary cells, shedding light on their unique roles in plant physiology.

Guard Cells

Guard cells are highly specialized cells that surround and control the opening and closing of stomata, which are tiny pores on the surface of leaves. These cells are characterized by their kidney or dumbbell shape, with a concave side facing the stomatal pore. Guard cells possess several unique attributes:

• Shape: As mentioned earlier, guard cells have a distinct kidney or dumbbell shape, which allows them to create a pore between them when they are turgid.
• Cell Wall Thickness: The cell walls of guard cells are unevenly thickened, with the inner wall being thicker than the outer wall. This asymmetrical thickening provides structural support and flexibility to the cells.
• Chloroplasts: Guard cells contain chloroplasts, which enable them to carry out photosynthesis. This is crucial as it provides the energy required for the active transport of ions and water, leading to changes in turgor pressure and stomatal opening or closing.
• Stomatal Pore: The stomatal pore is formed between two guard cells. When the guard cells are turgid, the pore opens, allowing gas exchange and transpiration. Conversely, when the guard cells lose turgidity, the pore closes, preventing excessive water loss.
• Regulation: The opening and closing of stomata are regulated by various factors, including light intensity, humidity, temperature, and the plant's water status. Guard cells respond to these stimuli by changing their shape and turgor pressure, ultimately controlling the size of the stomatal pore.

Subsidiary Cells

Subsidiary cells are specialized cells that surround and support the guard cells. They are typically smaller and more numerous than guard cells, forming a ring-like structure around them. Although subsidiary cells do not directly control stomatal opening and closing, they play essential roles in facilitating the function of guard cells. Here are some key attributes of subsidiary cells:

• Shape: Subsidiary cells are generally smaller and more rectangular in shape compared to guard cells. Their shape allows them to tightly pack around the guard cells, providing structural support.
• Cell Wall Thickness: The cell walls of subsidiary cells are relatively thin compared to guard cells. This thinness allows for flexibility and easy movement, enabling the subsidiary cells to adjust their position in response to changes in guard cell turgor pressure.
• Regulation: While subsidiary cells do not directly regulate stomatal opening and closing, they contribute to the overall coordination of stomatal behavior. They respond to chemical signals from the guard cells and neighboring cells, transmitting information and assisting in the fine-tuning of stomatal movements.
• Support: Subsidiary cells provide physical support to the guard cells, helping maintain their shape and preventing them from collapsing. This support is crucial for the proper functioning of guard cells in controlling stomatal aperture.
• Protection: Subsidiary cells also act as a protective barrier for the guard cells. They shield the guard cells from excessive mechanical stress, such as wind or physical damage, ensuring their integrity and functionality.

Conclusion

Guard cells and subsidiary cells are two distinct cell types that work together to regulate stomatal opening and closing in plant leaves. While guard cells directly control the size of the stomatal pore, subsidiary cells provide support, protection, and coordination to ensure the optimal functioning of guard cells. Guard cells possess a unique shape, uneven cell wall thickness, chloroplasts, and the ability to respond to environmental stimuli. On the other hand, subsidiary cells have a different shape, thinner cell walls, and contribute to the overall coordination of stomatal behavior. Together, these two cell types play a vital role in maintaining plant water balance, gas exchange, and overall plant physiology.