Who Cares About Centrioles?

Meristematic cells are found in the apical meristem of shoots and roots, as well as in lateral meristems in lateral buds and in the cambia (both vascular cambium and cork cambium).

Meristematic cells are quite different from the "typical" cell you have already learned about. They have thin walls, little to no vacuole, are tightly packed (no intercellular spaces), have immature organelles (proplastids rather than mature chloroplasts), are so small that the nucleus occupies a very large proportion of the total cell volume, and the cells live almost exclusively upon energy from respiration in their mitochondria.

Meristematic cells function almost exclusively in cell division (mitosis plus cytokinesis). This is an important topic. We have discovered that this topic is a weakness in your background based upon our outcomes assessment (Comprehensive Exam) process. The department has decided that cell division must be taught in every course. Here goes!

The Cell Cycle

Cells have a life cycle of cell division, followed by a length of time leading up to the next cell division. This cycle can be depicted as a pie representing the total lifetime of one cell cycle.

The small slice at the top of this pie represents mitosis ending in cytokinesis (more on that below). The rest of the pie represents the time between cell divisions...most of the life of a cell. We call this part of the cell cycle interphase. Inter- means between and so that is an appropriate name for this phase between cell divisions.

Interphase can be divided into three slices of time: G1, S, and G2.

Cells that do not actively divide (are NOT meristematic) are stuck in either G1 or G2 and their cell cycle does not complete. Human neurons are a good example; collenchyma in plants is another. Meristematic cells, by comparison, rapidly cycle and it is likely that their G1 and G2 phases are rather short. Of course during interphase it is important to make addtional organelles and so on in preparation for the upcoming cytokinesis.

Mitosis means the division of the nucleus. The process has four phases:

Cytokinesis, literally cell division, occurs next. In plants this means that a new wall and cell membranes must be laid down between the two re-forming nuclei within the cell. This is accomplished by packing the polymers or at least subunits into vesicles at the Golgi (dictyosome). The vesicles coalesce in a plane between the two nuclei. How do they "know" where to go? Gosh more work for your generation of scientists! The coalescence of the vessicles and polymerization of the wall material between them is usually not complete. Instead, cytoplasmic strands connect between the two cells. These are called plasmodesmata, and are an important feature of plant cells. The importance of these connections through the walls should not be underestimated! Transport in phloem and xylem, and indeed a variety of compounds through and throughout the life of a plant are carried out in these channels.

Slides of each phase of the cell cycle, both electron micrographs and light micrographs are shown in this lecture. When I get some digitizing equipment, I will illustrate this page more thoroughly.

This page © Ross E. Koning 1994.

The MLA citation style for this page would be:
Koning, Ross E. "Centrioles What?". Plant Physiology Website. 1994. http://koning.ecsu.ctstateu.edu/plant_biology/centriolehtml (your visit date).

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