We’ll explore one of the adaptations that allowed plants to venture from the water onto dry land. Learn about the function of the cuticle, then test your knowledge with a short quiz.
The Move to Life on Land
Many hundreds of millions of years ago, plants started to leave the confines of water and colonize land. One of the very first hurdles they had to conquer was how they were going to prevent drying out. Some did this by staying only in damp environments.
, but others were more adventurous and wanted to venture further inland. These plants needed some adaptations to help them conserve water. One of these adaptations was the cuticle.
The Cuticle and the Stomata
The cuticle is a waxy, water-repellent layer that covers all of the above-ground areas of a plant. It is secreted by the epidermis, the outer layer of the plant, and covers up any holes or chinks between the cells. This waxy layer keeps all of the plant’s valuable water inside where it belongs.
However, while the cuticle closes up any areas where the plant could lose water, it also closes up any place that allows the plant to breathe. Remember, plants are the reverse of us; they take in carbon dioxide and release oxygen. Plants rectified this problem through the creation of pores in the leaf called stomata.The stomata are bordered by a pair of cells called guard cells, which regulate, or guard, the stomata openings.
When there is a lot of water available, the guard cells are wide open, allowing the free exchange of carbon dioxide and oxygen between the plant and the environment. However, when water is scarce, the plant loses too much water through transpiration. This is a specific type of evaporation – the evaporation of water from the open stomata in plants; the fact that this process has its own term should be an indication of how significant it is to plants. In this case, the guard cells shut, closing off the stomata.For example, in the desert where rain is scarce and the sun is hot, plants have to take water loss very seriously. Cacti and other nocturnal plants, such as agave, have especially thick cuticles to help stop water loss, but they also don’t open their stomata at all during the day.
All gas exchange occurs overnight when the heat and sun cannot cause them to lose their precious water.
Additional Benefits of the Cuticle
On top of preventing water loss, it turns out that the cuticle is helpful to the plant in many other ways. Similar to our skin, the cuticle blocks some of the sun’s UV rays and acts as a barrier to bacteria, viruses, and other harmful microbes. Additionally, it provides some support, allowing those land-loving plants to grow taller than mere moist mosses.Cutin is the waxy substance that makes up the cuticle. It’s especially noticeable on some fruits, like apples or cherries, that can be buffed until they’re shiny.
The cutin from the carnauba palm is harvested and sold as palm wax or Brazil wax. Palm wax is used in everything from car wax, shoe polish and surfboard wax, to candy coating and lipstick.
As plants moved from water onto land, they needed to figure out the puzzle of how to keep from drying out. One of the solutions was the waxy cuticle that covers the entire outside of the above-ground parts of a plant. The water-resistant cuticle traps all of the plant’s valuable water inside, where it belongs.
Stomata are pores in the plant’s epidermis that allow the plant to breathe. However, water can be lost through these pores through the process of transpiration. For this reason, plants also have a pair of guard cells that surround the stomata. If, during the process of gas exchange with the environment, the plant is losing too much water, the guard cells close.
The cuticle has the added benefit of blocking UV rays, acting as a barrier to bacteria and disease, and providing some structural support for the plant.