• The shoot apical meristem consists of four distinct cell groups: • Stem cells • The immediate daughter cells of the stem cells • A subjacent organizing center • Founder cells
    for organ initiation in surrounding regions These four distinct zones are maintained by a complex signalling pathway.

  • [28][29] Secondary meristems There are two types of secondary meristems, these are also called the lateral meristems because they surround the established stem of a plant
    and cause it to grow laterally (i.e., larger in diameter).

  • Division of meristematic cells provides new cells for expansion and differentiation of tissues and the initiation of new organs, providing the basic structure of the plant

  • Differentiated plant cells generally cannot divide or produce cells of a different type.

  • Rice also contains another genetic system distinct from , that is involved in regulating stem cell number.

  • [19] Root apical meristem and tissue patterns become established in the embryo in the case of the primary root, and in the new lateral root primordium in the case of secondary

  • This allows a constant supply of new cells in the meristem required for continuous root growth.

  • This process known as mericloning, has been shown to reduce or eliminate viruses present in the parent plant in multiple species of plants.

  • Evidence suggests that the QC maintains the surrounding stem cells by preventing their differentiation, via signal(s) that are yet to be discovered.

  • It harbors two pools of stem cells around an organizing center called the quiescent center (QC) cells and together produces most of the cells in an adult root.

  • One of these indications might be the loss of apical dominance and the release of otherwise dormant cells to develop as auxiliary shoot meristems, in some species in axils
    of primordia as close as two or three away from the apical dome.

  • Often several branches will exhibit this behavior after the removal of apical meristem, leading to a bushy growth.

  • [21] Diversity in meristem architectures[edit] The SAM contains a population of stem cells that also produce the lateral meristems while the stem elongates.

  • [citation needed] Cells of the inner or outer cortex in the so-called “window of nodulation” just behind the developing root tip are induced to divide.

  • Cells at the shoot apical meristem summit serve as stem cells to the surrounding peripheral region, where they proliferate rapidly and are incorporated into differentiating
    leaf or flower primordia.

  • Cells of this zone have a stem cell function and are essential for meristem maintenance.

  • Medullary tissue There are two types of apical meristem tissue: shoot apical meristem (SAM), which gives rise to organs like the leaves and flowers, and root apical meristem
    (RAM), which provides the meristematic cells for future root growth.

  • [25] Also, it has been proposed that the mechanism of KNOX gene action is conserved across all vascular plants, because there is a tight correlation between KNOX expression
    and a complex leaf morphology.

  • [26] Primary meristems Apical meristems may differentiate into three kinds of primary meristem: • Protoderm: lies around the outside of the stem and develops into the epidermis.

  • All plant organs arise ultimately from cell divisions in the apical meristems, followed by cell expansion and differentiation.

  • Primary growth gives rise to the apical part of many plants.

  • [citation needed] There are three types of meristematic tissues: apical (at the tips), intercalary or basal (in the middle), and lateral (at the sides also known as cambium).

  • [10] acts to promote cellular differentiation by repressing WUS activity outside of the central zone containing the stem cells.

  • [citation needed] Recent investigations into apical dominance and the control of branching have revealed a new plant hormone family termed strigolactones.

  • It turns out that the mechanism of regulation of the stem cell number might be evolutionarily conserved.

  • [9] Another important gene in plant meristem maintenance is WUSCHEL (shortened to WUS), which is a target of CLV signaling in addition to positively regulating CLV, thus forming
    a feedback loop.

  • This process involves a leaf-vascular tissue located LRR receptor kinases , peptide signalling, and interaction, similar to that seen in the system.

  • Indeterminate growth of meristems Though each plant grows according to a certain set of rules, each new root and shoot meristem can go on growing for as long as it is alive.

  • In many plants, meristematic growth is potentially indeterminate, making the overall shape of the plant not determinate in advance.

  • Their growth is limited to the flower with a particular size and form.

  • In Arabidopsis thaliana, 3 interacting CLAVATA genes are required to regulate the size of the stem cell reservoir in the shoot apical meristem by controlling the rate of cell

  • The corpus and tunica play a critical part of the plant physical appearance as all plant cells are formed from the meristems.

  • As a result, the plant will have one clearly defined main trunk.

  • In that sense, the meristematic cells are frequently compared to the stem cells in animals, which have an analogous behavior and function.

  • Intercalary meristems are capable of cell division, and they allow for rapid growth and regrowth of many monocots.

  • At the meristem summit, there is a small group of slowly dividing cells, which is commonly called the central zone.

  • The primary meristems in turn produce the two secondary meristem types.

  • In contrast, nodules on pea, clovers, and Medicago truncatula are indeterminate, to maintain (at least for some time) an active meristem that yields new cells for Rhizobium

  • The mechanism of apical dominance is based on auxins, types of plant growth regulators.

  • Primary growth leads to lengthening of the plant body and organ formation.

  • Thus, soybean (or bean and Lotus japonicus) produce determinate nodules (spherical), with a branched vascular system surrounding the central infected zone.

  • Recent findings indicate that QC can also act as a reservoir of stem cells to replenish whatever is lost or damaged.


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