The Phragmoplast

Plant cells are enclosed by a rigid cell wall, making it difficult for cells to divide by contracting from the outside. Hence, plant cells divide by forming a new cell wall between the two daughter nuclei in an “inside out” fashion. A specialized structure in plants called the phragmoplast guides the new cell wall formation.

The plane of cell division, which is the future site of cell wall formation, is marked by a preprophase band made up of microtubules and actin filaments that forms during the G1 phase of the cell cycle. The preprophase band assembles at the cell cortex and disappears at the beginning of the M phase.

During mitosis, chromosomes separate and start moving to opposite poles. At the poles, the nuclear envelope forms around the separated chromosomes and the spindles start to disappear. The remaining microtubules of the mitotic spindle form the phragmoplast.

The phragmoplast microtubules are polar, with plus ends near the equatorial plane, and minus ends near the poles.

Golgi bodies secrete small vesicles that are carried by motor proteins along the microtubules to the cell center. These vesicles are filled with polysaccharides and glycoproteins, two important compone