Plant Cell Wall

Cellulose

consists of parallel beta 1-4 glucan chains bundled into microfibrils

cellulose provides

stiffness, tensile strength, and a strong structure

hemicellulose

Matrix polysaccharides that associate non-covalently with cellulose

hemicellulose provide

structural integrity, bridge microfibrils, and help form hydrated wall

pectin

hydrated matrix polysaccharides found primarily in the primary cell wall and middle lamella

pectin provide

hydration, gel formation, flexibility, and control wall porosity

lignin

aromatic polymer deposited mainly in secondary cell walls

lignin provides

support for upright growth, rigidity, water transport support, and resistance to pathogens

Middle lamella

pectin-rich layer holding adjacent cells together

Cellulose is synthesized

at the plasma membrane by cellulose synthase complexes

Hemicellulose and pectins are synthesized

in the Golgi apparatus and secreted via exocytosis

Lignin monomers are synthesized

in the cytosol and ER, exported across plasma membrane into the apoplast

Primary wall

Deposited during active cell growth;
thin, flexible, and rich in cellulose, hemicellulose, and pectin

Secondary wall

Deposited inside primary wall after cell expansion stops;
thick, rigid, and reinforced with lignin

celllulose made of

Beta-1,4-linked D-glucose chains

lignin made of

complex cross-linked phenolic polymers derived from monolignols

hemicellulose made of

diverse sugar backbones with sugar branch substituents

pectin made of

galacturonic acid and other sugar monomers

functions of plant cell wall

maintains cell shape against turgor pressure, acts as defense barrier against pathogens, mediates cell-to-cell signaling, and prevents desiccation

plasmodesmata

allow direct intercellular communication and transport of water, nutrients, hormones, and signaling molecules