Upper vs Lower Epidermis
It is the stomata that makes the main difference between upper and lower epidermis of leaves. Animals possess skin as their outer most cover of the body. Similar to that, plants have a layer called epidermis as their outermost cover. Epidermis originates from the protoderm. The outermost layer of the apical meristem and leaf primordium is called the protoderm. The whole plant body is covered by this single cell layered epidermis. Epidermis can be differentiated into upper and lower epidermis when it occurs on the upper and lower surfaces of a leaf. Therefore, upper (adaxial) surface and a lower (abaxial) surface of a leaf are called upper and lower epidermis respectively. Epidermal cells are barreled shaped and connected to each other in order to form the epidermis.
Special features exhibited by the epidermis are; the layer of cutin, guard cells, stomata, and trichomes. Both upper and lower epidermal cells secrete a waxy layer called cuticle. This layer helps to reduce the evaporation from leaves. The thickness of this layer varies according to the species and environmental conditions. Apart from that, leaf epidermis possesses several special cell types as guard cells and trichomes. The occurrence of these special structures varies on upper and lower epidermis.
The guard cells are bean or semi-lunar in shape (grasses consist of dumbbell shape guard cells). The minute pore surrounded by two guard cells is called a stoma. Unlike the epidermal cells, the guard cells have chloroplasts, thicker inner walls, and thin outer walls. They regulate the opening and closing of the stoma. Thus, transpiration is controlled by the guard cells. Furthermore, the guard cells are surrounded by two or more cells that are different from the usual epidermal cells called subsidiary cells. Stomata occurrence in the epidermis is varied in dicots and monocots.
What is Upper Epidermis?
Upper epidermis consists of barrel-shaped single cell layered epidermal cells. Epidermal cells in both monocots and dicots have the same shape and structure. Usually, the upper epidermis has a less number of guard cells compared to the lower epidermis. Some plants have stomata only on the upper epidermis; e.g. water lilies.
What is Lower Epidermis?
The Lower epidermis is similar to the upper epidermis in the formation and structure. However, occurrence of stomata and trichomes may differ according to the species and environmental conditions. Stomata are abundant in the lower epidermis of a dorsiventral leaf. Dessert plants possess sunken stomata at their lower epidermis.
What is the difference between Upper and Lower Epidermis?
Both upper and lower epidermises are derived from the apical and leaf primordium. Both epidermal layers consist of a single layer of barrel-shaped cells. Epidermal cells are tightly linked to each other and provide mechanical strength and protection from pathogens and other environmental conditions. Walls of the leaf epidermis consist of waxy substance known as cutin, which reduces the evaporation from the leaf. Some plants consist of subsidiary cells surrounding the guard cells of the epidermis.
• Stomatal Density:
• Upper epidermis’s stomatal density is lesser than that of lower epidermis.
• Stomata Content:
• Floating plants consists of stomata only on the upper epidermis.
• Submerged plants do not have stomata on either epidermal layers.
• Epidermis of Xerophytic Plants:
• The Upper epidermis of xerophytic plants does not contain stomata.
• Lower epidermis of xerophytic plants consists sunken stomata.
Images Courtesy:
- The lower epidermis of Tilia × europaea via Wikicommons (Public Domain)
- Lear tissue structure by Zephyris (CC BY-SA 3.0)
