Meristem

A meristem is a tissue in all plants that consists of meristematic cells. These are cells that have not yet a special function. They are in parts of the plant where growth can take place.

Plant cells with special functions (differentiated cells) generally cannot divide or produce cells of a different type. Therefore, cell division in the meristem is necessary to get new cells for expansion and differentiation of tissues and to create new organs, that are necessary for the basic structure of the plant body.

Meristematic cells have the same function for plants as stem cells have for animals. They are incompletely or not at all differentiated, and are capable of continued cellular division (youthful). And the cells are small and protoplasm fills the cell completely. The vacuoles are extremely small.

tunica-corpus model

Maintenance of the cells needs a balance between two antagonistic processes: organ initiation and stem cell population renewal.

Primary meristems

Apical meristems may differentiate into three kinds of primary meristem:

• Protoderm - around the outside of the stem and develops into the epidermis.
• Procambium - just inside of the protoderm and develops into primary xylem and primary phloem. It also produces the vascular cambium, a secondary meristem.
• Ground meristem develops into the pith. It produces the cork cambium, another secondary meristem.

These meristems are responsible for primary growth, or an increase in length or height.

Secondary meristems

There are two types of secondary meristems:

• Vascular cambium - produces secondary xylem and secondary phloem, this is a process which may continue throughout the life of the plant. This is what gives rise to wood in plants. Such plants are called arborescent. This does not occur in plants which do not go through secondary growth (known as herbaceous plants).
• Cork cambium - gives rise to the bark of a tree.

Other pages

• Cork cambium
• Vascular cambium

Wikimedia Commons has images, video, and/or sound related to:

Méristème

References

• Mauseth J.D.
• Neil A. Campbell and Jane B. Reece Biology, 6th edition. Benjamin Cummings.
• Schoof et al. The stem cell population of Arabidopsis shoot meristems is maintained by a regulatory loop between CLAVATA and WUSCHEL genes. Cell 100: 635-644.
• Research on meristems: meristemania.org [1]