What is the function of the lateral meristem

Meristem or Educational tissue refers to a type of tissue in plants that consists of undifferentiated cells and can be involved in growth through cell division.

The term "meristem" was first used by Carl Wilhelm von Nägeli (1817-1891) in his book "Contributions to Scientific Botany" in 1858. It is derived from the ancient Greek words merisein (μερίςειν), which means “to divide” and accordingly describes the fundamental empirically perceptible property of the meristems, and stemma (στέμμα) bandage, bundle.

Primary meristems are found both in the above-ground part of the plants at the extreme end of the shoot tips (shoot apical meristems) and at the extreme end of the side shoots (subapical meristems), as well as in the underground part, at the root tips (root apical meristems). The cells of the meristems usually have thin cell walls with little cellulose. In contrast to differentiated cell types, they can theoretically divide indefinitely. The growth of plants is generally based on the fact that shoot and root meristems at opposite poles of the plant continuously release cells through cell division to the plant body, which develop into the various organs shoot, root and leaf.

Comparison with animal stem cells

Meristematic cells in plants correspond to stem cells in animal organisms in that they share the property of being undifferentiated and the origin of all specialized cell types. The strict distinction between embryonic stem cells and fully differentiated adult cells, which can be made in animal organisms due to the unique plasticity of the stem cells, is less pronounced in plants. Even fully differentiated cells are able to dedifferentiate under certain conditions and to form new, completely different organs. This is illustrated by the formation of roots in cuttings, for example.

Classification of the meristems

  • 1. Primary meristems (are formed from apical meristems and are responsible for the primary growth of the plant)
    • 1.1 Protoderm (forms the outer covering tissue, the epidermis)
    • 1.2 Basic meristem (forms the medullary tissue and the secondary cork cambium)
    • 1.3 Prekambium (forms the conductive tissue)
  • 2. Secondary meristems (also lateral meristems, as the name suggests, serve to increase thickness)
    • 2.1 cambium (as cambium ring)
    • 2.2 Phellogen - also cork cambium (forms the secondary closing tissue, the periderm, with its three layers of tissue)
  • 3. Residual meristems, also tertiary meristems (larger meristematic cell complexes in an environment with already differentiated tissue)
    • 3.1 intercalar meristems (special case of the residual meristems, especially in shoot axes; meristems lying between already differentiated areas and causing local longitudinal growth)
    • 3.2 Meristemoids (meristematic cell groups or single cells that are ultimately converted into permanent tissue)

Secondary meristems

The young seedling initially only has a single primary shoot apical meristem, which is found between the two cotyledons in dicotyledonous plants and is created during embryogenesis. This meristem is responsible for the formation of the primary shoot axis through the production of shoots and leaves. The establishment of further shoot axes takes place through the creation of meristems in the axils of foliage leaves, which are referred to as axillary meristems or lateral meristems. The differently pronounced activity of the armpit meristems is a basis for the diverse growth forms in the plant kingdom. The activity of the axillary meristems is often initially suppressed by the primary shoot apical meristem, so that side shoots grow delayed. This control by the shoot apical meristem is called apical dominance. The formation of lateral root meristems does not take place in any anatomically defined area at a certain distance from the primary root meristem. Here is an inner layer of tissue called the pericycle, the origin of these lateral root meristems. In addition to the secondary meristems in the axils of the leaves and the root tips, the term lateral meristems also refers to the cambium and the phellogen, both cell layers which are active in dividing and which are responsible for the secondary growth of many plants in the outer area of ​​the shoot.

structure

Schematic representation of a shoot apical meristem divided into L1, L2 and L3 layers
The primary shoot apical meristem of the Bedecktsamer can be divided into different layers and zones. The outer layer of cells, the epidermis, is called the L1 layer. The cell layer below is the L2 layer. The L1 and L2 layers together represent the so-called tunica. The tissue lying further inside, which consists of more than one layer of cells, represents the L3 layer, which is also called the corpus. The cells of the first two layers only divide in an anticlinic orientation, which means that the offspring of cells in these layers generally remain in these layers. Cells of the L3-layer divide in an anti-and periclinic orientation, so that no individual cell layers can be separated from one another in the L3-layer. Another form of classification relates more to the function of the meristem. The actual stem cells are located in the central zone, which divide and release cells for differentiation to the peripheral zone of the meristem. In this peripheral zone, the cells begin to differentiate into the lateral organs such as the leaves. Below the central zone is the rib zone, which mainly contributes to the growth of the shoot.

development

The sprout apical meristem is theoretically able to continue its division activity almost indefinitely, and this also happens frequently, as for example with trees. However, depending on numerous factors such as external influences, position on the plant or the age of the plant, the shoot meristem terminates just as often by going through various stages of development and finally transforming into a flower meristem that ceases its activity with the production of a flower. The final lateral organs produced by the meristem within this set program are sepals, petals, stamens, and carpels, in that order. Flowers are terminated apical meristems.

See also

Web links

Individual evidence

Strasburger - Textbook of Botany, Andreas Bresinsky, Christian Körner, Joachim W. Kadereit, Gunther Neuhaus, Uwe Sonnewald, Spektrum Akademischer Verlag, 36th edition 2008 ISBN 978-3-8274-1455-7