In a fully grown animal, its stem cells are restricted to producing cells of a particular tissue. For example, the stem cells which divide to replace your blood cells can only divide to become blood cells. These stem cells therefore are crucial for repair. There is currently a lot of interest in the potential for the use stem cells in the treatment of disease. Plants grow by a combination of cell division and cell elongation. Cell division in plants only occurs at meristems.
Meristems are found at various points in the plant as shown in the diagram below. Meristems can be found at the root and shoot tips which allows the stem and root to lengthen. Meristems can also be found in the stem between the phloem cells and the xylem, we'll learn more about these later in this unit.
Meristems in the stem allows it to thicken to give the stem support as it grows. Meristems divide to form unspecialised cells which can then become any type of plant cell. Here's a little video which discusses meristems in a little more detail. Search this site. Dedifferentiation: a new approach in stem cell research. Bioscience 57, — Chan, S. Gardening the genome: DNA methylation in Arabidopsis thaliana. Damri, M. Senescing cells share common features with dedifferentiating cells.
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Pina, A. In addition, protoderm cells continually differentiate to produce new epidermal cells of the roots that ensure that new root hairs continue to be formed given that they have a short lifespan a few days.
In the roots, protoderm plays an important role in the formation of root hairs that are involved in the absorption of nutrients and water in their environment. The epidermis which is, for the most part, a single cell layer also covers all organs in the stem of plants thereby acting like a protective layer. Although cells of the ground meristem are a type of primary meristem, as is the case with protoderm cells and cells of the primary procambial, they are segregated and thus set apart from the other cells.
Division of these cells results in the production of the cortex, pith as well as a number of other related tissues. Cells of the ground meristem, therefore, contribute to the growth and development of the plant through the formation of such parts as the root cortex.
The endodermis, located in the inner layer of the cortex helps regulate the accumulation of minerals in the roots and thus to other parts of the plant. As the origin of ground tissue systems, cells of the ground meristem are involved in the production of three main types of cells that include:. Parenchyma - Although they may take up a variety of shapes, most parenchyma cells are spherical or elongated in shape. They may also have two cell walls a thin primary wall as well as a secondary wall consisting of a polylayer known as lignin.
These cells play a number of important roles related to metabolism e. For instance, while the pith is the site of storage for most plants, the mesophyll in leaves is the site of photosynthesis. Collenchyma - Cells of the collenchyma cells serve to provide support to young stems and leaves when they differentiate.
In young stems, they can be found beneath the epidermis as the outer cells of cortex. With regards to structure, collenchyma cells are elongated whose walls consist of cellulose and pectin.
Thickening observed at the corner of their cell walls contributes to their supportive function. Sclerenchyma - Like collenchyma cells, cells that make up the sclerenchyma also serve to provide supportive functions.
As such, they also have a thicker secondary cell wall that consists of lignin. They include fibers that are elongated cells which act like strengthening cables and sclereids of varying shapes that either exist as solitary cells or in clusters.
Compared to the fibers, sclereids have thicker cell walls that help support the weight of plant organs. As a result, they cannot provide the flexible support observed in collenchyma cells. The procambium is composed of elongated cells that are characterized by a large nucleus, dense cytoplasm, and proplastids. Differentiation of these cells results in the production of the vascular tissue of the plant primary xylem and phloem in plants.
Various types of vessels develop at different stages and serve different functions. Protoxylem - Involved in the transportation of water as the plant roots elongate. The presence of annular rings in the protoxylem also provide supportive function. Metaxylem - Found in elongated parts of the roots and are involved in the exchange of water and minerals. Phloem cells - Located between the arms of the protoxylem and form the phloem. They are involved in the transportation of food material during the adult life of the plant.
Cells of the intercalary meristem are located between the segments of non-meristematic organs e. These cells are said to originate from primary meristematic cells and tend to lose their meristematic nature as they gradually become permanent.
These cells are found in monocot plants such as grass bamboo etc. Cells that make up the lateral meristem are characterized by their rectangular shape that develops along one plane.
They are characterized by a rectangular shape, vacuoles in their protoplasm as well as tannins. Essentially, stem cells are undifferentiated cells of multicellular organisms that give rise to both the same type of cells as themselves as well as other types of cells through differentiation.
As in animals, stem cells in plants are located in stem cell niches known as meristems protomeristem and primary meristem. Here, plant cells that are regarded as stem cells are undifferentiated and located in the very tips of the plant. Compared to stem cells in animals, studies have shown that stem cells in the meristem can be restored even in cases where they have been removed. In the event that favorable conditions are provided, this allows the plant to continue growing.
According to studies, meristem cells can arise from differentiated cells.
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