Preprophase

Preprophase is a brief period in the cell cycle of plant cells that precedes prophase. It is unique to higher plants and is characterized by the formation of a preprophase band (PPB). The PPB is a transient ring of microtubules located just beneath the plasma membrane at the future site of cell division. It is not a component of the spindle apparatus itself.

The PPB is assembled and disassembled relatively quickly, typically appearing late in interphase and disappearing by the time the nuclear envelope breaks down in prophase. Its primary function is to determine the plane of cytokinesis, the process by which the cytoplasm divides to form two daughter cells. The PPB acts as a scaffold, guiding the formation of the cell plate, which will eventually separate the two new cells.

The organization of the PPB is dependent on the cytoskeleton, specifically microtubules. While its exact assembly mechanism is still under investigation, it is known that certain proteins are involved in its formation and stabilization. The presence and role of the PPB highlight a key difference in cell division mechanisms between plant and animal cells. Animal cells, lacking a cell wall, utilize a contractile ring of actin filaments and myosin for cytokinesis, and do not form a PPB. The PPB serves as a crucial signaling center for cytokinesis in plants, ensuring accurate cell division and tissue development.