Monocot Vs. Dicot Roots Overview

Definition of Monocot Root

Monocot roots are fibrous or adventitious roots that develop from the stem and are made up of a large network of thin roots and root fibers.

• Depending on the type and age of the plant, monocot roots can vary greatly. However, most monocot plants are herbaceous and lack a robust cambium that may support woody tissues.
• The many roots that make up the monocot root system are distinguished by their complexity and rate of development. The primary or taproot and any related lateral roots make up the root system.
• Additionally, seminal roots that are produced in an ungerminated seed are present. Monocot plants also tend to have shoot-borne roots or accidental roots. Other parts of the seed besides the radical are developed by the adventitious roots.
• Monocots have two different types of adventitious roots: those that start at nodes on the germination axis that are below the soil and those that start at nodes that are above the soil. The second type of adventitious roots, also known as prop or brace roots, is often seen at the lowermost 2-3 nodes.
• Monocot plants lack cambium in their roots, which prohibits the development of robust, woody plants and restricts the plant’s ability to expand sufficiently.
• As a result of the absence of cambium in the roots, adventitious roots, or shoot-borne roots, emerge, which provide the plant support and sturdiness.
• Monocot plants begin to establish their major roots during early embryogenesis, and they develop into a separate area within 10 to 15 days. The major root is then encased in a protective sheathing structure during vascular development.

Definition of Dicot Root

Dicot roots are taproots made up of one primary root from which secondary and tertiary roots sprout and spread through the soil in a vertical fashion.

• The non-green, below-the-soil portion of the plant, known as the roots, lacks nodes and internodes.
• Although the structure of the roots of dicot plants is generally similar, the length, thickness, and complexity of the root system can vary.
• A few dicot plants may have modified roots for respiration, food storage, and mechanical support, among other functions.
• The root cap, meristematic zone, zone of elongation, and zone of maturity are the main components of a typical root.
• The taproot, which extends deeply and vertically to form the main root of the dicot root system, Secondary roots that may grow sideways and downwards emerge from the taproot.
• Tertiary roots may develop from the secondary roots to go deeper and allow for the absorption of water and nutrients. The dicot root system also contains tiny root hairs.
• Depending on the plant type, dicot roots can range in texture from woody to herbaceous. Large plants with thick stems can develop because the cambium in the woody root system allows for this.

Structure of Monocot and Dicot Root

The following components make up the internal structure of both monocot and dicot plants:

1. Piliferous Layer or Epiblema or Epidermis

• The uppermost layer of roots, known as the epidermis or epiblema, is made up of a dense layer of parenchymatous cells with thin walls and polygonal shapes but no intercellular gaps.
• The root’s epidermis lacks a cuticle and stomata. Some epidermal cells give birth to specific root hairs in the maturation zone of both monocot and dicot roots.
• The layer is also known as the piliferous layer because it lacks intercellular gaps and has hair cells.
• Trichoblasts, which create hair, and atrichoblasts, which don’t form hair at the roots, make up the epidermis, also known as the rhizodermis, in monocots.
• Monocot plants, like orchids, have a unique, multilayered epidermis that is known as the velamen. Gas exchange occurs within the velamen.
• The exodermis, which is lignified and suberinized in older roots, replaces the short-lived epidermis. The outermost cortical cells, forming a Casparian band, give rise to the exodermis.
• The epidermis and other root tissues are peeled off in dicot roots and then replaced with cork cambium.
• The monocot plant’s epidermis survives and develops a protective cuticula in shoot-borne roots.
• In both root varieties, the epidermis protects the interior tissues. Because they have a bigger surface area, the tiny root hairs increase the soil’s ability to absorb water and nutrients.

2. Cortex

• The tissue found under the epidermis is called the cortex, and it is made up of several layers of cortical cells.
• Monocots have thin-walled, multilayered parenchymatous cortical cells with adequate intercellular distances between them.
• However, in addition to parenchyma, the cortex of dicot roots also contains sclerenchyma.
• The cortex’s cells lack chlorophyll, making them non-photosynthetic like the epidermal cells. Some dicot plants, including Tinospora and Trapa, are photosynthetic and have chlorophyll in their cortex cells.
• In certain plants, the cells in the cortex’s outer layer go through a process called suberization to create an exodermis that may have one or more layers.
• Leucoplasts are present in the cells in this area, which also store starch in the form of starch grains. The cortex’s most crucial job is transferring water from the epidermis to the interior tissues.
• Compared to the cortex of dicot roots, the area of the cortex in monocot roots is larger because it can have up to eighteen layers of parenchymatous cells.

3. Endodermis

• Between the cortex and the core vascular tissues of the root, there is another layer of dermal tissue called the endodermis. The endodermis is an obstruction between the two layers.
• There are no intercellular gaps, and the cells are closely packed into barrel shapes. Often, there is only one layer of cells in the endodermis.
• A layer of Casparian strip is present inside the juvenile endodermis cells as a strip of suberin and lignin. The strip loses its distinguishability as the cells mature because the cells thicken.
• Monocot plants develop their adventitious roots from the endodermis’ interior layer of cells.
• The protoxylem groups of the vascular bundles are on the other side of the young cells.
• These cells are also known as passage cells or transfusion cells due to their role in transmitting fluids from the cortex and the vascular bundles both inwardly and externally. Protoxylem cells and passage cells both have the same number.
• Through the use of their plasmodesmata, the thicker or older endodermis cells participate in fluid flow as well.
• As a biological checkpoint, the endodermis controls the fluid flow between the cortex and the vascular tissue.

4. Pericycle

• The endodermis, the most unique layer of cells between dicot and monocot roots, is found underneath the pericycle, a single-layered structure.
• Monocots have a single layer of sclerenchymatous cells, and only a few parenchymatous cells make up their pericycle. Due to the deposition of different materials, the immature cells of this layer have thin walls that subsequently thicken.
• In dicot roots, the pericycle is made up of prosenchyma, a form of parenchyma distinguished by its profusion of protoplasm.
• Depending on the monocot, the pericycle may be uniseriate or single-layered (as in maize) or multiseriate or multilayered (Smilax).
• In dicots, lateral roots come from a region of the pericycle that is situated across from the protoxylem. As a result, dicots have endogenous lateral roots.
• The pericycle has a role in developing the vascular cambium in dicot roots.
• Dicot plants also develop cork cambium during secondary development. Monocot roots do not develop the cambium.
• The production of lateral roots, cambium, and support for the vascular tissue that lies underneath the pericycle make it an essential component of the root tissue.

5. Vascular Bundles

• The plant’s roots’ deepest tissues, the vascular bundles, are made up of alternating xylem and phloem units. Dicots and monocots have different numbers of vascular bundles in their roots.
• Radial and exarch vascular bundles are seen in dicots, and their numbers range from two to six (diarch to hexarch). There may be a polyarchy situation with more than six vascular bundles in some plants, such as Ficus.
• Although there are usually more than six vascular bundles in monocots, they are also radial and exarch. Twenty to thirty vascular bundles are seen in maize roots, but more than one hundred bundles may be seen in pandanus and palms.
• The vascular bundles are organized in the shape of a ring around the central pith in both types of roots. Since the xylem and phloem are arranged differently, the vascular bundles are also known as radial bundles.
• Both monocot and dicot roots have xylem bundles that are exarch; the protoxylem is located on the pericycle, and the metaxylem is located in the middle (pith).
• In contrast to the dicot, which has polygonal and thick-walled cells, the monocot’s xylem is made up of oval vessels and xylem parenchyma.
• Protoxylem vessels in tin dicots exhibit annular thickenings, whereas metaxylem vessels have reticulate thickenings. Dicot roots lack xylem parenchyma and fibers as well.
• Dicots have phloem bundles that are present right next to the pericycle and are made up of companion cells, sieve tubes, and phloem parenchyma. Phloem fibers are not present.
• Although the metaphloem and protophloem of the phloem are also separated, they are difficult to tell apart.
• Monocots have phloem bundles that are closer to the pith and have a similar composition of cells and structures.
• Phloem bundles are involved in the conduction and storage of food, whereas the xylem tissue in roots is engaged in the conduction of water via the roots.

6. Conjunctive tissues

• Between the xylem and phloem bundles in the vascular tissue are masses of parenchymatous or sclerenchymatous cells known as conjunctive tissues.
• Because there are more vascular bundles in monocot roots than in dicot roots, there is a greater quantity of conjunctive tissue.
• During secondary growth in dicot plants, the pericycle and conjunctive tissues combine to form the vascular cambium. Monocot roots do not produce a cambium.
• These tissues help to store food while also giving mechanical root support.

7. Pith

• The pith is the center mass of tissues in the root’s circulatory system, made up of parenchymatous cells with thin walls.
• The pith is less developed or less pronounced in dicots. Additionally, it could not exist at all in other circumstances.
• However, in monocots, the pith is noticeable and has a large number of spherical or polygonal cells.
• Large intercellular gaps separate the loosely connected pith cell layers. The pith’s cells serve as food storage units and aid in air circulation among the vascular bundles.

8. Passage Cells

• The endodermis’ distinct passage cells are responsible for transferring water and other substances from the cortex to the vascular bundles.
• Dicot roots do not have any passage cells, while monocot roots do. Transfusion cells are another name for these cells.
• The younger Casparian strip-like cells of the layer that do not have deposits of suberin or lignin are the passage cells of the endodermis.
• The passage cells, which are frequently found close to the protoxylem, allow material to move radially through the root system.

Functions of Monocot and Dicot Root

1. Both monocot and dicot plants rely on their roots to maintain the plant, which is their primary role. Additionally, roots serve a number of additional more or less comparable roles in both types of plants.
2. Some of the roles played by monocot and dicot roots include the following:
3. The root system’s primary job is to attach the plant to the ground or other surfaces in order to give support.
4. Water and minerals dissolved in the soil must be absorbed by roots. The water and minerals are subsequently transported to other areas of the plant through the vascular system in the root.
5. Additionally, the root system stores numerous food particles in various tissues, including conjunctive tissue, pith, and cortex. Plants with modified roots, like radishes and carrots, may store a lot of food.
6. In order to get oxygen, plants that thrive in marshy places have roots that extend above the soil line. Pneumatophores are the names given to these roots, which include microscopic holes called pneumathodes that are engaged in gas exchange.
7. Many dicot roots share a symbiotic connection with fungi and other microbes that are crucial to nitrogen fixation.
8. Some plants’ multiplication and plant dispersion processes include their roots.

Examples of Monocot Root

1. Maize root

• The fibrous or adventitious root system of maize is made up of multiple short-borne roots that are present above the soil’s surface.
• Due to the absence of cambium in the root, monocots require shoot-borne roots. These roots provide the plant with the stability it needs to grow tall enough. Four to five nodes of the stem above the soil’s surface are where you may see maize’s adventitious roots.
• A single maize plant may use 200 cubic feet of soil and take in 30–35 gallons of water while it is growing.
• The plant’s lateral roots can extend up to 3–4 feet on all sides and reach depths of 5–6 feet into the earth, depending on the kind of soil.
• The coleorhizae, a protective sheath that surrounds the maize plant’s major root, allows the root to penetrate the seed coat.
• Like other monocot seeds, maize seeds have three to seven seminal roots that start their development both laterally and vertically.

2. Orchid roots

• Monocot plants, like orchids, are typically grown as ornamental plants for aesthetic purposes. There are two types of orchids: terrestrial and epiphytic.
• Orchids that grow on the ground have fleshy, thick roots used for storage.
• In contrast, the modified aerial roots of the epiphytic orchids are lengthy and made up of a unique component known as velamen.
• The layer of dead cells known as velamen is found on the roots of orchids. These serve as a mechanism for absorbing moisture and nutrients from the environment.
• Healthy orchid roots are firm and range in color from green to white. Most of the time, the roots are only green just before they require watering. Continuously green roots are a sign of too much water.
• The optimal moment to re-pot an epiphytic orchid in a new pot for its proliferation is frequently indicated by the new roots that are starting to emerge.

Examples of Dicot Root

1. Banyan tree roots

• The tap root systems of banyan trees are distinctive, frequently accompanied by aerial prop roots that develop into thick, woody trunks.
• As trees get older, the secondary roots blend together with the main roots. The lateral roots start to cover a large area by extending laterally in all directions.
• The intricacy of the banyan root is a result of the tree’s trunk becoming heavier as it grows.
• Throughout the plant’s lifespan, the roots continue to expand as new cells are introduced to the meristematic portion of the root.
• The strongest component of the root is the tip, which is made up of dead cells.
• As a result, as the root grows, hard rocks can be penetrated.

2. Roots of garden peas

• Garden peas have a straightforward tap root system comprising a main root with several branches that only extend 6 inches into the soil.
• Different bacteria coexist in symbiotic relationships with the secondary roots of peas. These microorganisms may be found in the root nodules of plants, where they participate in nitrogen fixation.
• These plants’ roots are crucial to the biogeochemical cycle of nitrogen because the bacteria there can convert air nitrogen into forms the plants can use.
• The root nodules may be seen on the secondary and tertiary roots of the root system.

References and Sources

• Hochholdinger F. (2009) The Maize Root System: Morphology, Anatomy, and Genetics. In: Bennetzen J.L., Hake S.C. (eds) Handbook of Maize: Its Biology. Springer, New York, NY. https://doi.org/10.1007/978-0-387-79418-1_8
• Feldman L. (1994) The Maize Root. In: Freeling M., Walbot V. (eds) The Maize Handbook. Springer Lab Manuals. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-2694-9_4
• Yadegari R., Goldberg R.B. (1997) Embryogenesis in Dicotyledonous Plants. In: Larkins B.A., Vasil I.K. (eds) Cellular and Molecular Biology of Plant Seed Development. Advances in Cellular and Molecular Biology of Plants, vol 4. Springer, Dordrecht. https://doi.org/10.1007/978-94-015-8909-3_1
• Hochholdinger Frank, Marcon Caroline, Baldauf Jutta A., Yu Peng, Frey Felix P. Proteomics of Maize Root Development. Frontiers in Plant Science. VOL 9, 2018; pg 143. DOI:10.3389/fpls.2018.00143. https://www.frontiersin.org/article/10.3389/fpls.2018.00143.
• Zhang, Shibao et al. “Physiological diversity of orchids.” Plant diversity vol. 40,4 196-208. 25 Jun. 2018, doi:10.1016/j.pld.2018.06.003
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