Primary wall

Extensible. Cellulose microfibrils: extruded from plasma membrane, cellulose synthase complex at the plasma membrane and oriented by microtubules. Matrix of pectin, hemicellulose and structural proteins exported in vesicles from Golgi. Cross-linking is affected by highly glycosylated proteins: Hydroxyproline-rich glycoproteins (extensions), Proline-rich proteins and Arabinogalactan proteins. Generally, cellulose has high tensile strength, orientation of the microfibrils determines cell growth and shape and cells without cell wall are spherical.