Dermal Tissue

Epidermal tissues include several specialized cells, such as pavement cells, trichomes, and guard cells, each performing specific functions in the plant.

Similar to our skin, dermal tissue acts as plants’ first line of defense. It protects plants from external injuries and attacks from parasites such as viruses, bacteria, and fungi. Thus, it helps the plant to keep healthy.

Apart from defense, dermal tissues perform a specific role in the plant organs, leaves, roots, and roots.

In Leaves

Pavement cells, the large, irregularly shaped parenchymal cells lacking chloroplast, are most numerous in the leaf epidermis. They protect and keep the inner cells of the leaf in place, prevent excessive water loss, and maintain internal temperature.

The epidermal cells secrete a waxy chemical, the cuticle, which prevents excessive water loss by transpiration and thus helps the plant to survive a hot day. The cuticle also helps absorb water, commonly seen as water balls on the leaves after rain.

The minute pores in the leaves allow the exchange of gases such as oxygen and carbon dioxide with the environment. The relative opening and closing of the pore control photosynthesis and respiration in plants. A pair of bean-shaped guard cells flank each pore. The pore, and the guard cell, are collectively called stomata (singular: stoma). 

In Roots

Here, the epidermis helps absorb water and essential minerals from the soil. Trichomes, the specialized root hair structures on the epidermis that are extensions of epidermal cells, increase the surface area of absorption. They also reduce evaporation due to wind, reflect solar radiation, collect moisture, and provide protection against frost.

Specialized dermal cells called endodermis serve as a checkpoint for entering materials into the vascular system. The presence of a waxy substance on the walls of the epidermal cells, known as the Casparian strip, helps in the entry of water and solutes by crossing the plasma membrane.  . 

In Stems

Like leaves, the pavement cells in the stems help to protect the delicate inner parts of the epidermis, reduce water loss, and maintain the internal temperature. Stomata perform gas exchange, while trichomes increase water absorption, decrease water loss by transpiration, increase solar reflectance, and store substances that defend the leaves against predation by herbivores.