The chemical substances found most abundantly in the middle lamella are released into the phragmoplast by the Golgi complex.
In plants, two nearby cells are joined together by the middle lamella. The middle lamella is mainly composed of calcium and magnesium pectates. The middle lamella also contains carbohydrates such as galactose, arabinose, and xylose. These chemicals are synthesized in the Golgi apparatus, packaged in secretory vesicles, and later released into the phragmoplast, which later becomes the middle lamella.
The phragmoplast started forms after the disappearance of the spindle fibers in the late phase of cytokinesis. During anaphase and telophase of the cell cycle, microtubules, microfilaments, membranes, and associated molecules are assembled perpendicularly to the site for future cell plates. The structure leads to the formation of a new cell wall and separates the two daughter nuclei. Failure of phragmoplast assembly causes incomplete cytokinesis that leads to the formation of multinucleated cells.
Microtubules are polymers of tubulin proteins. They can grow as long as 50 µm and are part of the cytoskeleton. They provide structural shape to the eukaryotic cells. Microfilaments are polymers of actin proteins and are also a part of the cytoskeleton.
The microtubules transport the Golgi vesicles to the midline of the phragmoplast. These vesicles are fused to form the cell plate and polysaccharides become the middle lamella. The Golgi vesicles membrane becomes the plasma membrane of the newly developed daughter cells.