FRAGMOPLAST: definition and function

The plant eukaryotic cells They are cells that are surrounded by a cell wall made up mainly of cellulose (structural polysaccharide). Thanks to this wall, plant cells are rigid and support themselves. The presence of this wall is a great advantage at a structural level. But how does a plant cell divide, despite the rigidity of this wall? To answer this question, in this lesson from a TEACHER we will look at the definition and function of the fragmoplast.

Index

1. What is the fragmoplast: easy definition
2. Structure and composition of the fragmoplast
3. What is the function of the fragmoplast

The fragmoplast is a exclusive structure of the vegetables cells It appears during cytokinesis or late cytodieresis and is responsible for the division of the cell cytoplasm, through the formation of a septum that separates it into two parts. It is a transitional structure that only appears when the cell is dividing.

The cytokinesis It is the last phase of the cell cycle that takes place after the telophase of mitosis or meiosis. Consists of the

In the cytokinesis of plant cells, it is produced by the formation of a septum in the middle of the cell, which will give rise to the two daughter cells.

The fragmoplast is a cellular structure composed of microtubules, contractile microfibers, and vesicles from the Golgi complex.

1-. Microtubules of the fragmoblast

Microtubules are protein structures formed by tubulin. They are linear and rigid in shape and are assembled to form a kind of scaffolding. Microtubules are responsible for transporting substances and organelles within the cell. In the fragmoplast, the microtubules are arranged in two opposing bundles, close to the equatorial zone (middle zone) of the cell and oriented perpendicular to the plane of division. They are thicker microtubules than those that form the achromatic spindle during mitosis or meiosis.

2-. Fragmoblast microfibers

They are the thinnest fibers of the fragmoplast. They are mainly made up of actin. Actin is a globular protein that forms microfibers that have the ability to contract. Together with microtubules, they are responsible for directing the Golgi complex vesicles to the equatorial zone of the cell.

3-. Vesicles

Vesicles are bags limited by cell membrane that contain, inside, the polysaccharide compounds that will form the new cell wall. They come from the dictyosomes (set of flattened and stacked sacs surrounded by microtubules and vesicles) of the Golgi complex. The Golgi apparatus synthesizes polysaccharides important for cell wall synthesis and acts as a distribution center for material in the cell cytoplasm.

The vesicular route By default, when the plant cell divides, it is the one that directs the vesicles generated in the Golgi apparatus to the equatorial zone of the cell.

Vesicles provide the fundamental elements for the formation of the central plaque and subsequently the cell wall:

• The plasma membrane that limits the vesicles will go on to form the new cell membrane segments of the two daughter cells.
• The content of the vesicles will be deposited in the middle zone, to configure the middle lamina. Is about non-cellulosic polysaccharides.

Image: Biology for All

The function of the fragmoplast is the formation of a septum in the equatorial zone of the cell, which will later give rise to the cell wall that will separate the two new cells. This septum in formation is called middle sheet.

During the later phase of cytokinesis, actin microtubules and microfibers act to guide vesicles toward the equatorial zone of the dividing cell. That is, the vesicular transport in itineraries defined by the disposition of microtubules and microfibers. The vesicles directed towards the equatorial zone contain non-cellulosic polysaccharides that will make up the initial separation septum that is called cell plate.

Upon reaching the middle of the cell, the vesicles fuse with each other, giving rise to a structure limited by the plasma membrane from the fused vesicles. Inside this membranous structure of the fragmoplast, the so-called middle plate is formed, which is semi-rigid and will give rise to the middle lamina. The formation of the middle plate by the fragmoplast begins in the central zone of the cytoplasm and progresses towards the edges of the cell. For this reason the cell wall is said to have a centrifugal growth, that is, from the innermost area of ​​the cytoplasm towards the extremes.

In parallel to the centrifugal growth of the cell plate, its consolidation begins to give rise to the middle sheet of the cell wall. Plaque consolidation occurs through the incorporation of small amounts of cellulose, which is the biomolecule responsible for the rigidity and strength of the cell wall. In these initial stages, the wall formed has a certain resistance but is not rigid, which allows it to adapt to the increase in size that the growth of the cell supposes.

The middle lamina is the first layer that is formed of the three that make up the cell wall. The other two layers (primary and secondary wall) are subsequently formed below this first layer.

The two cells formed can remain in contact through cytoplasmic channels called plasmodesms. These channels are formed when the complete fusion of the vesicles that form the cell plate in the fragmoblast does not take place.

Once the formation of the cell wall that separates the two daughter cells is completed, the fragmoplast disappears because new vesicular routes are established through the restructuring of microtubules and microfibers.

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R. Paniagua Gomez. (2007). Plant and animal cytology and histology. Madrid: McGraw-Hill Interamericana