Malcolm Rivera
The pericycle is a layer of cells in plants that encircles the vascular tissue in stems and roots. It is the outermost cell layer of the central cylinder of the root and gives rise to branch and secondary roots. The pericycle is composed of one or two layers of parenchyma or sclerenchyma cells. It is located between the endodermis and phloem in plant roots and is surrounded by the inner cortical layer, the endodermis. In dicot stems, it is situated around the ring of vascular bundles in the stele. The pericycle is a primary root tissue that forms the cell layer surrounding xylem, phloem, and procambium cells.
| Characteristics | Values |
|---|---|
| Description | The pericycle is a layer of cells in plants that encircles the vascular tissue in stems and roots. |
| Location | The pericycle is the outermost cell layer of the central cylinder of the root. It is located between the endodermis and phloem in plant roots. |
| Composition | The pericycle is composed of parenchyma or sclerenchyma cells. |
| Function | The pericycle gives rise to branch roots and regulates the formation of lateral roots. |
| Cell Layers | The pericycle is typically surrounded by one or two layers of cells. |
| Cell Division | Pericycle cells possess continued cell division activity long after leaving the root apical meristem. |
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What You'll Learn
- The pericycle is the outermost cell layer of the central cylinder of the root
- It is composed of non-vascular parenchyma cells
- Pericycle cells can divide and initiate lateral root primordia
- The pericycle is a primary root tissue that surrounds xylem, phloem, and procambium cells
- Pericycle cells are considered true stem cells
The pericycle is the outermost cell layer of the central cylinder of the root
The pericycle is a unique layer of cells that encircles the vascular tissue in plant stems and roots. It is a primary root tissue that forms the outermost cell layer of the central cylinder of the root. The pericycle is a crucial component of the root architecture, giving rise to branch and lateral roots.
The pericycle is composed of parenchyma or sclerenchyma cells, which are non-vascular in nature. However, it is still considered part of the vascular cylinder as it arises from the procambium, similar to the vascular tissues it surrounds. The pericycle is located between the endodermis and phloem in plant roots, contributing to the formation of the vascular cambium.
In dicot roots, the vascular cambium originates entirely from a portion of pericycle tissue. The pericycle regulates the formation of lateral roots by rapidly dividing near the xylem elements of the root. This process is influenced by hormones and genes, such as the HRGPnt3 gene found in tobacco plants. The pericycle's ability to initiate lateral roots is regulated by factors like ALF4 and is limited in scope.
The pericycle is divided into two populations, with cells at the xylem pole and phloem pole exhibiting differences in size, ultrastructure, and gene expression. Xylem pole pericycle (XPP) and phloem pole pericycle (PPP) cells differ in their cell division and organogenesis capabilities. The pericycle's prolonged cell division activity, even after leaving the root apical meristem, contributes to root branching and secondary growth.
The pericycle's ability to maintain cell division competence has led to the concept of an "extended meristem," highlighting the flexibility of plant roots in responding to changing soil environments. The formation of new organs, such as callus, from the pericycle further underscores its significance in plant development and regeneration capacity.
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It is composed of non-vascular parenchyma cells
The pericycle is a unique layer of cells in plants, encircling the vascular tissue in stems and roots. It is the outermost cell layer of the central cylinder of the root and gives rise to secondary root initials. The pericycle is a primary root tissue that forms a cell layer surrounding xylem, phloem, and procambium cells. In Arabidopsis, the pericycle layer can be recognised in the hypocotyl but not in the shoot.
The pericycle is composed of non-vascular parenchyma cells. It is a heterogeneous, non-vascular tissue in plants that is divided into two populations—one at the xylem pole and one at the phloem pole. Pericycle cells at these poles differ in size, ultrastructural features, and specific proteins and gene expression. The pericycle is located between the endodermis and phloem in plant roots. In dicot stems, it is situated around the ring of vascular bundles in the stele.
The pericycle is a crucial part of the root architecture. It regulates the formation of lateral roots by rapidly dividing near the xylem elements of the root. Pericycle cells possess proliferative activity long after leaving the root apical meristem. Pericycle cell division leads to the production of lateral roots, vascular cambium, periderm, and callus. In this way, pericycle cell division underlies root branching and secondary growth, as well as plant regeneration capacity.
The pericycle's ability to maintain cell division competence has led to the concept of an 'extended meristem'. This is regarded as the basis for the high flexibility of plant roots to respond to an ever-changing environment in the soil. Pericycle cells can be considered true stem cells. In Arabidopsis, the onset of periderm development follows the first cell division in vascular cambium formation. The first cell divisions in the periderm developmental program are longitudinal anticlinal divisions of XPP cells, which increase the cell number of the pericycle layer.
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Pericycle cells can divide and initiate lateral root primordia
The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and constitutes the outermost part of the stele of plants. It is composed of non-vascular parenchyma cells and is considered part of the vascular cylinder. In eudicots, the pericycle has the capacity to produce lateral roots. The pericycle is the outermost cell layer of the central cylinder of the root and gives rise to secondary root initials.
In Arabidopsis, pericycle cells adjacent to the protoxylem poles of the vascular cylinder continue to cycle without interruption during the passage through the elongation and differentiation zones. However, only some of these dividing pericycle cells undergo the asymmetric, formative divisions that give rise to LRPs. The estimated duration of a pericycle cell cycle in the root apical meristem is similar to the interval between cell displacement from the meristem and the initiation of LRP formation. The decision by xylem pole pericycle cells to form an LRP is taken in the basal meristem, which is immediately behind the primary root apical meristem.
The pericycle regulates the formation of lateral roots by rapidly dividing near the xylem elements of the root. In dicot roots, the vascular cambium originates from a portion of pericycle tissue. The pericycle gives rise to the vascular tissue of the lateral roots, and they are therefore defined as pericyclic LRs. Monocot roots rarely branch, but when they do, the branch originates from the pericycle.
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The pericycle is a primary root tissue that surrounds xylem, phloem, and procambium cells
The pericycle is composed of non-vascular parenchyma or sclerenchyma cells and is located just inside the endodermis, forming the outermost part of the stele of plants. It is considered part of the vascular cylinder due to its origin from the procambium and its association with the vascular tissues it surrounds. In eudicots, the pericycle has the capacity to produce lateral roots, which are initiated by the pericycle cells becoming "founder" cells. These founder cells undergo cell cycling and give rise to developing organs.
The pericycle is typically surrounded by a single cell layer of endodermis. In dicot roots, it strengthens the roots and safeguards the vascular bundles. Additionally, the pericycle contributes to the vascular cambium, which is responsible for the formation of secondary xylem and phloem. The vascular cambium is completely secondary in origin and originates from a portion of pericycle tissue.
The pericycle is also involved in the evolution of lateral root (LR) formation. It has been observed that the recruitment of pericycle cells near vascular tissues is a common factor in the evolution of LR branching in seed plants, Equisetopsida, and leptosporangiates. This suggests a positional ancestral competence for LR development.
The structure of the pericycle varies, and it can consist of one or two layers of cells. Its unique ring structure distinguishes it from other parts of the plant and facilitates its identification. The pericycle is an essential tissue in plant roots, contributing to their growth, development, and protection.
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Pericycle cells are considered true stem cells
The pericycle is a layer of cells in plants that encircles the vascular tissue in stems and roots. It is a primary root tissue that forms a single cell layer surrounding xylem, phloem, and procambium cells. In roots, it is surrounded by the inner cortical layer, the endodermis. The pericycle is the outermost cell layer of the central cylinder of the root and gives rise to secondary root initials. It regulates the formation of lateral roots by rapidly dividing near the xylem elements of the root.
The pericycle is crucial for the overall root architecture, and its ability to initiate new organs and undergo organogenesis highlights its significance in plant regeneration capacity. Pericycle cells at the xylem pole, known as 'founder cells,' retain the capacity for asymmetric cell division, even as they move higher up in the root among differentiated cells. This division results in the formation of lateral roots, vascular cambium, periderm, and callus, contributing to root branching and secondary growth.
The molecular pathways underlying pericycle cell division competence are diverse and influenced by developmental stages and external stimuli. While much remains to be discovered about the pericycle, its role in plant growth and adaptation is undeniable. The ability of pericycle cells to initiate lateral roots and influence root architecture showcases their true stem cell nature, providing plants with the regenerative capabilities necessary to adapt and thrive in their environment.
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Frequently asked questions
The pericycle is generally a layer of one or two layers of cells.
The pericycle is the outermost cell layer of the central cylinder of the root. It lies just inside the endodermis and is the outermost part of the stele of plants.
The pericycle regulates the formation of lateral roots. It gives rise to branch roots and vascular tissue.
