It is easy to see some plants get taller, but it is important to know that plants must also have a strong support that we cannot always see.
Root growth helps plants survive and can happen in two ways.
Root System Growth
As plants grow above the surface, there is also growth that occurs within the soil. Roots need to grow in order to better support the plant and to better absorb both water and nutrients for the growing plant.
We will review some structures of the root in addition to looking at how roots grow.
The Root Cap
You can think of root growth as a construction site. The root is creating new cells in order to expand and help the plant further develop. When at a construction site, people are required to wear hardhats in order to protect their heads.
In roots, the root cap serves a similar purpose. This outer area of the bottom of the root protects other root tissues as the root continues to grow into the soil.The cells in the root cap are specialized for several different things. First, they can sense gravity, which is why roots grow down. Second, they secrete a slimy substance that helps roots move through the soil. We can see the root cap in the diagram below.
The cells formed here eventually create the three tissues needed for primary root growth: protoderm, procambium and ground meristem.
The protoderm will eventually become the epidermis, or skin of the root. The procambium will eventually become the vascular tissue.Remember that there are two types of vascular tissue: xylem to move water and phloem to move food. The procambium will produce cells that make both types of tissues. The third type of cell created in the meristematic region is the ground meristem, which will become ground tissue and help with storage of water and nutrients for the plant.
The next region involved in primary root growth is the elongation region. This is the area of root lengthening. The cells that were produced in the meristematic region grow in the elongation region. No new cells are produced here, but this is the area that actually creates the growth of the root.
We can see in this diagram that the cells in this area actually do look longer than those in the meristematic region.
The third region involved in primary root growth is the maturation region.
As the name implies, this is the area of cell maturation. It is also where the cells that grew in the elongation region fully develop and become adult cells. The three different primary cells that were created in the meristematic region fully develop into the cells they were designed to become.The protoderm cells become the epidermis, which is like the root skin. The epidermis cells move to the outer layers of the root in order to provide protection.
The procambium cells either become xylem – to carry water – or phloem – to carry food. Lastly, the ground meristem cells become the ground tissue of the root, which is basically all the other cells, such as those found in the cortex of the root.
Lateral Root Growth
Much like some plants have primary and secondary growth, roots may also have more than just primary growth. Lateral root growth occurs after primary root growth and allows for increases in surface area to improve absorption and for support of the plant.Lateral roots start to develop in the pericycle, which is the outermost cell layer in the vascular cylinder. Remember that the xylem and phloem make up the vascular cylinder and that it is found in the center of the root. We can see the pericycle in the diagram below.
Notice that it is the outer layer of the vascular cylinder in the middle of the root. Because lateral roots start at the vascular cylinder, they are able to contain vascular tissue.
Root growth is vital to the survival of plants. Both primary and lateral roots can be produced. In order to protect the growing cells, the root cap is at the tip of the root.
Behind the root cap are three regions involved in primary root growth, including areas for cell division, growth and maturation.The meristematic region is the location of cell division, which means this is where new cells are made. The new cells then move into the elongation region in order to increase in size.
They lastly move into the maturation region where the three different primary cells that were created in the meristematic region fully develop into the cells they were designed to become. The protoderm cells become the epidermis or skin of the root, the procambium cells either become xylem – to carry water – or phloem – to carry food, and the ground meristem cells become the ground tissue of the root, which is basically all the other cells, such as those found in the cortex of the root.In lateral root growth, cells on the outer layer of the vascular bundle push through the ground tissue and epidermis in order to reach the outside of the root. These lateral roots stay connected to the xylem and phloem. Both primary and lateral root growth help increase the absorption of water and nutrients for the plant.
At the end of this lesson, you should be able to:
- Identify the parts of the root structure
- Explain how lateral root growth works