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2.2: The regions of the root

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    When a seed is germinating, one of the first things to emerge from the seed coat is the root. This initial “root” is called a radicle and as it grows it gives origin to the root system. To understand how roots grow, we need to take a peek inside of a growing root. If we look at a root tip, we can recognize four root regions: the root cap, the region of cell division, the region of elongation and the region of maturation (Figure \(\PageIndex{1}\)). All of these regions are usually found within the first few centimeters of the root tip, so we are talking about a very small area.

    Figure \(\PageIndex{1}\): Regions of the Root by Openstax is licensed under CC BY 4.0.

    Root Cap

    A root growing into the soil faces physical challenges, like friction and potential damage from rock particles present in the soil. The root cap is a mass of cells (parenchyma cells) located at the tip of the root that protects it from mechanical damage. It also secretes a slimy substance called mucilage to help the root grow more smoothly into the soil. The root cap also plays a role in the plant perception of gravity (gravitropism), which makes plant roots always grow downward (Figure \(\PageIndex{2}\)).

    Root tip Longitudinal section.png
    Figure \(\PageIndex{1}\): Root tip Longitudinal section. By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr. Modified to include labels. A derivative of the original work of "Apical Meristem in Allium Root Tip" is licensed under Public Domain via Wikicommons.

    The region of cell division

    The region of cell division is found just under the root cap. In this region, cells are perpetually dividing (mitosis), meaning there is a constant generation of new cells, causing the root to grow in length (primary growth). These regions of active cell division in plants are found in the growing tips of roots and stems, and they are called apical meristems.

    The region of elongation

    Following the region of cell division is the region of elongation. When new cells are created in the apical meristem of the root they are small and rounded. In this region they grow in size, lengthening the root as they grow. The cells in this region are still undifferentiated; therefore they do not have a specific function yet.

    The Region of Maturation

    Following the region of elongation comes the final one, the region of maturation, where cells differentiate and become a specific type of cell. It is here that cells get their final function assigned depending on where they are located in the root. For example, cells in the center of the root will become specialized in transport (xylem and phloem), while the cells towards the periphery (outside) of the root will become specialized in protecting the root (epidermis).

    In this region of maturation is also where root hairs are formed. Root hairs are extensions of some epidermal cells in the region of maturation (Figure \(\PageIndex{2}\)). They extend the surface area of each cell, increasing their absorption capacity. In fact, most of the water and mineral absorption happens in the root hairs; therefore plants have massive amounts of them (in the range of several billion in a mature plant).

    Root hairs are delicate and only survive for several days, but as the root grows, new root hairs are formed in the region of maturation. Root hairs can be easily damaged if you are transplanting seedlings to a new pot, which may limit the seedling’s ability to absorb water and nutrients.

    This page titled 2.2: The regions of the root is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Daniela Dutra Elliott & Paula Mejia Velasquez.